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QUALITY/57ADE2F31A28ABBE3A9B8074) Please download to view (https://documents.tips/download/link/meat-processing-improving-quality) Meat processing Related titles from Woodhead’sfood science, technologyand nutri tion list: Meat refrigeration (ISBN: 1 85573442 7) Basedon

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the work of the internationallyrenownedFoodRefrigerationandProcess EngineeringResearchCentre(FRPERC)at the University of Bristol, this will be the standardwork on meatrefrigeration,coveringboth individual quality issuesandthe managementof the cold chain from carcassto consumer. Lawrie’s meatscienceSixth edition (ISBN: 1 85573395 1) This book remainsa

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conceptionof the animal until humanconsumption,presentingthe fundamentalsof meatscience.This sixth edition

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incorporatesthe significantadvancesin meatsciencewhich havetakenplace during the pastdecadeincluding our

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standardfor both studentsandprofessionalsin the meatindustry. It providesa systematicaccountof meatsciencefrom the

increasinglypreciseunderstandingof the structureof the muscle,aswell as the identificationof the aberrationsin DNA which leadto the developmentof BSE syndromein meat. HACCPin the meatindustry (ISBN: 1 85573448 6) Following the crisesinvolving BSE andE.coli, the meatindustryhasbeenleft with an enormousconsumerconfidenceproblem.In order to regainthe trust of the general public the industrymustestablishandadhereto strict hygieneandhazardcontrol systems.HACCP is a systematicapproachto the identification,evaluationandcontrol of food safetyhazards.It is beingappliedacrossthe world, with countriessuchasthe US, Australia,New Zealandandthe UK leadingthe way. However,effective implementationin the meatindustry remainsdifficult andcontroversial.This book is a surveyof key principlesandbestpractice,providing an

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authoritativeguide to making HACCP systemswork successfullyin the meatindustry. Detailsof thesebooksanda completelist of Woodhead’sfood science,technology andnutrition titles canbe obtainedby: • visiting our web site at www.woodheadpublishing.com • contactingCustomerServices(email: [email protected];fax: +44 (0) 1223893694;tel.: +44 (0) 1223891358ext. 30; address:WoodheadPublishing Limited, Abington Hall, Abington,CambridgeCB1 6AH, England) If you would like to receiveinformationon forthcomingtitles in this area,pleasesend your addressdetailsto: FrancisDodds(address,tel. andfax asabove;e-mail: [email protected]).Pleaseconfirm which

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subjectareasyou are interestedin. Meat processing Improving quality Edited by JosephKerry, John Kerry and David Ledward Publishedby WoodheadPublishingLimited Abington Hall, Abington, CambridgeCB1 6AH England www.woodhead-

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published2002,WoodheadPublishingLimited andCRC PressLLC ß 2002,WoodheadPublishingLimited The

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authorshaveassertedtheir moral rights. This book containsinformationobtainedfrom authenticandhighly regardedsources.

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publishing.com Publishedin North Americaby CRC PressLLC 2000CorporateBlvd, NW BocaRatonFL 33431 USA First

Reprintedmaterialis quotedwith permission,andsourcesare indicated.Reasonable efforts havebeenmadeto publishreliabledataandinformation,but the authorsand the publisherscannotassumeresponsibilityfor the validity of all materials.Neither the authorsnor the publishers,nor anyoneelseassociatedwith this publication,shall be liable for any loss,damageor liability directly or indirectly causedor allegedto be causedby this book. Neither this book nor any part may be reproducedor transmittedin any form or by any means,electronicor mechanical,including photocopying,microfilming and recording,or by any information-storageor retrievalsystem,without permissionin writing from the publishers. The consentof WoodheadPublishingLimited andCRC PressLLC doesnot extend to copyingfor generaldistribution,for promotion,for

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creatingnew works,or for resale.Specificpermissionmustbe obtainedin writing from WoodheadPublishing Limited or CRC PressLLC for suchcopying. Trademarknotice:Productor corporatenamesmay be trademarksor registered trademarks,andareusedonly for identification andexplanation,without intent to infringe. British Library Cataloguingin PublicationData A cataloguerecordfor this book is availablefrom the British Library. Library of CongressCataloging-inPublicationData A catalogrecordfor this book is availablefrom the Library of Congress. WoodheadPublishingLimited ISBN 1 85573583 0 (book); 1 85573666 7 (e-book) CRC PressISBN 0-8493-1539-5 CRC Pressordernumber:WP1539 Coverdesignby Martin Tacchi Projectmanagedby MacfarlaneProductionServices,Markyate,Hertfordshire ([email protected]) Typesetby MHL TypesettingLimited, Coventry,Warwickshire Printedby TJ InternationalLimited, Padstow,Cornwall, England Contributors . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . xi 1 Introduction . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 1 D. Ledward, The University of Reading 2 Defining meat quality . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 3 T. Becker, University of Honenheim, Stuttgart 2.1 Introduction: what is quality? . .. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 3 2.2 Consumer perceptions of quality . . . . . .. . . . . . . . . . . . . . . . . . . . . . . . 6 2.3 Supplier perceptions of quality .. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 14 2.4 Combining consumer and supplier perceptions: the quality circle . . .. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 16 2.5 Regulatory definitions of quality . . . . . .. . . . . . . . . . . . . . . . . . . . . . . . 19 2.6 Improving meat

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and meat product quality . . . .. . . . . . . . . . . . . . . . . 21 2.7 References . . . . .. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 23 Part I Analysing meat quality . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 25 3 Factors affecting the quality of raw meat . . . . . .. . . . . . . . . . . . . . . . . 27 R. K. Miller, Texas A & M University, College Station 3.1 Introduction . . .. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 27 3.2 Quality meat composition and structure . . . . . .. . . . . . . . . . . . . . . . . 27 3.3 Breed and genetic effects on meat quality . . . .. . . . . . . . . . . . . . . . . 37 3.4 Dietary influences on meat quality . . . .. . . . . . . . . . . . . . . . . . . . . . . . 49 3.5 Rearing and meat quality. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 52 3.6 Slaughtering and meat quality . .. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 52 3.7 Other influences on meat quality . . . . . .. . . . . . . . . . . . . . . . . . . . . . . . 56 Contents 3.8 Summary: ensuring consistencyin raw meatquality . . . . . . . . . . 56 3.9 Futuretrends . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 57 3.10 References . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 57 4 The nutri tional quality of meat . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 64 J. Higgs, Food to Fit, Towcesterand B. Mulvihill, Republicof Ireland 4.1 Introduction . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 64 4.2 Meat andcancer . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 66 4.3 Meat, fat content anddisease . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 69 4.4 Fatty acidsin meat . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 71 4.5 Proteinin meat . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 78 4.6 Meat asa ‘functional’ food . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 79 4.7 Meat andmicronutrients . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 82 4.8 Futuretrends . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 88 4.9 Conclusion .

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. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 92 4.10 References . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 92 5 Lipid- derived flavors in meat products . . . . . . . . . . . . . . . . . . . . . . . . 105 F. Shahidi, Memorial University of Newfoundland, St John’s 5.1 Introduction . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 105 5.2 The role of lipids in generation of meatyflavors . . . . . . . . . . . . . . 106 5.3 Lipid autoxidation andmeatflavor deterioration . . . . . . . . . . . . . . 108 5.4 The effect of ingredientson flavor quality of meat . . . . . . . . . . . . 110 5.5 The evaluationof aromacompoundsandflavor quality . . . . . . . 116 5.6 Summary . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 117 5.7 References . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 117 6 Modelling colour stability in meat . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 122 M. Jakobsenand G.

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Bertelsen,Royal Veterinary and Agricultural University, Frederiksberg 6.1 Introduction . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 122 6.2 Externalfactors affectingcolour stability during packaging andstorage . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 123 6.3 Modelling dynamic changes in headspacecomposition . . . . . . . . 123 6.4 Modelling in practice: fresh beef . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 124 6.5 Modelling in practice: cured ham . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 128 6.6 Internal factorsaffectingcolour stability . . . . . . . . . . . . . . . . . . . . . . 131 6.7 Validation of models . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 133 6.8 Futuretrends . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 134 6.9 References . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .

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. . . . . . . . . . . . . . . . . . . . 135 7 The fat content of meat and meat products . . . . . . . . . . . . . . . . . . . . . 137 A. P. Moloney, Teagasc,Dunsany 7.1 Introduction . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 137 7.2 Fat andthe consumer. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 138 vi Contents 7.3 The fat contentof meat . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 138 7.4 Animal effects on the fat content andcompositionof meat . . . 141 7.5 Dietary effects on the fat content andcompositionof meat . . . 144 7.6 Futuretrends . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 147 7.7 Sourcesof further information andadvice . . . . . . . .

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. . . . . . . . . . . . . 149 7.8 References . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 150 Part II Measuring quality . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 155 8 Qualit y indicators for raw meat . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 157 M. D. Aaslyng,Danish Meat Research Institute, Roskilde 8.1 Introduction . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 157 8.2 Technological quality . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 157 8.3 Eatingquality . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 160 8.4 Determining eating quality . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 166 8.5 Samplingprocedure. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 166 8.6 Futuretrends . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .

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. . . . . . . . 168 8.7 References . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 168 8.8 Acknowledgemnts . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 174 9 Sensoryanalysisof meat . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 175 G. R. Nute,Universityof Bristol 9.1 Introduction . . . . . . . . . . . . . . . . . . . .

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. . . . . . 176 9.3 Sensorytests . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 178 9.4 Categoryscales

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. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 185 9.5 Sensoryprofile methodsandcomparisons with

Food

. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 175 9.2 The sensory panel . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .

instrumental measurements . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 186 9.6 Comparisonsbetween countries . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 189 9.7 Conclusions . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 189 9.8 References . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .

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. . . . . . . . . . . . . . . . . . . . . 199 10.4 Analysing meatproperties usingNIR spectrophotometry . . . . . 201 10.5 Measuring

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meat colour andotherproperties . . . . . . . . . . . . . . . . . . 201 10.6 Water-holding capacity . . . . . . . . . . . . . . . . . . . . . . . . .

Food

. . . . . . . . . 190 10 On-line monitoring of meat quality . . . . . . . . . . . . . . . . . . . . . . . . . . . . 193 H. J. Swatland, University of Guelph 10.1 Introduction . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 193 10.2 Measuring electrical impedance . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 195 10.3 Measuring pH . . . . . . . . . . . . . . . . . . . . . . . . . . .

. . . . . . . . . . . . . . 203 10.7 Sarcomerelength . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 203 10.8 Connective tissue . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 204 10.9 Marbling andfat content . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 206 10.10 Meat flavour . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 207 10.11 Boar taint . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 207 Contents vii 10.12 Emulsions . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 207 10.13 Measuring changes during cooking . . . . . . . . . . . . . . . . . . . . . . . . . . . 208 10.14 Conclusion . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 211 10.15 Sources of further informationandadvice . . . . . . . . . . . . . . . . . . . 211 10.16 References . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 212 11 Microbiolo gical hazard identification in the meat industry . . . 217 P. J. McClure, Unilever Research, Sharnbrook 11.1 Introduction . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 217 11.2 The main hazards . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 218 11.3 Analytical methods . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 231 11.4 Futuretrends . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 233 11.5 Sources of further informationandadvice . . . . . . . . . . . . . . . . . . . . . 234 11.6 References . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 234 Part III New techniquesfor improvi ng quality . . . . . . . . . . . . . . . . . . . . . . 237 12 Modelling beef cattle production to improve quality . . . . . . . . . . 239 K. G. Rickert, University of Queensland,Gatton 12.1 Introduction . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 239 12.2 Elements of beefcattle production . . . . . . . . . . . . . . . . . . . . . . . . . . . . 240 12.3 Challenges for modellers . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 244 12.4 Simplemodel of herdstructure . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 251 12.5 Futuredevelopments . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 254 12.6 References . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 255 13 New developments in decontaminating raw meat . . . . . . . . . . . . . . 259 C. James,Food Refrigeration and Process EngineeringResearch Centre (FRPERC),Universityof Bristol 13.1 Introduction . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 259 13.2 Current decontamination techniquesandtheir limitations . . . . . 260 13.3 Washing . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 262 13.4 The useof chemicals . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 263 13.5 New methods:steam . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 267 13.6 Othernew methods . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 272 13.7 Futuretrends . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 273 13.8 Sources of further informationandadvice . . . . . . . . . . . . . . . . . . . . . 276 13.9 References . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 277 14 Automated meat processing . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 283 K. B. Madsen and J. U. Nielsen,DanishMeat ResearchInstitute, Roskilde 14.1 Introduction . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 283 14.2 Current developmentsin roboticsin the meatindustry . . . . . . . . 284 14.3 Automation in pig slaughtering. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 285 viii Contents 14.4 Casestudy: the evisceration process. . . . . . . . . . . . . . . . . . . . . . . . . . . 287 14.5 Automation of secondary processes . . . . . . . . . . . . . . . . . . . . . . . . . . . 290 14.6 Futuretrends . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 294 14.7 References andfurther reading . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 296 15 New developments in the chilling and freezing of meat . . . . . . . 297 S.J James,Food Refrigeration and Process Engineering Research Centre(FRPERC),University of Bristol 15.1 Introduction . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 297 15.2 The impactof chill ing andfreezingon texture . . . . . . . . . . . . . . . . 299 15.3 The impactof chill ing andfreezingon colour . . . . . . . . . . . . . . . . . 300 15.4 The impactof chill ing andfreezingon drip lossand evaporativeweight loss . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 302 15.5 The cold chain . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 304 15.6 Temperature monitoring . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 306 15.7 Optimising the design andoperationof meatrefrigeration . . . . 308 15.8 Sourcesof further information andadvice . . . . . . . . . . . . . . . . . . . . . 310 15.9 References . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 310 16 High pressure processing of meat . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 313 M. de Lamballerie-Anton,ENITIAA, Nantes, R. Taylor and J. Culioli, INRA, Theix 16.1 Introduction:high pressuretreatmentandmeatquality . . . . . . . . . 313 16.2 Generaleffect of high pressureon food components . . . . . . . . . . 314 16.3 Structuralchanges dueto high pressuretreatmentof muscle . . 315 16.4 Influenceon enzyme release andactivity . . . . . . . . . . . . . . . . . . . . . . 318 16.5 High pressureeffectson the sensoryandfunctionalproperties of meat . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 318 16.6 Pressureassisted freezing andthawing . . . . . . . . . . . . . . . . . . . . . . . . 320 16.7 Effectson microflora . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 321 16.8 Currentapplicationsandfuture prospects . . . . . . . . . . . . . . . . . . . . . 323 16.9 References . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 324 17 Processing and quality control of restructured meat . . . . . . . . . . 332 P. Sheard,University of Bristol 17.1 Introduction . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 332 17.2 Productmanufacture . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 333 17.3 Factorsaffecting product quality: temperature,ice content, particlesizeandmechanicalproperties . . . . . . . . . . . . . . . . . . . . . . . . 338 17.4 Factorsaffecting product quality: protein solubility and relatedfactors . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 343 17.5 Factorsaffecting product quality: cooking distortion . . . . . . . . . . 347 17.6 Sensoryandconsumer testing . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 349 17.7 Futuretrends . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 351 Contents ix 17.8 Sources of further informationandadvice . . . . . . . . . . . . . . . . . . . . . 353 17.9 References . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 353 18 Quality control of fermented meat products . . . . . . . . . . . . . . . . . . . 359 D. Demeyer, Ghent University and L. Stahnke, Chr. Hansen A/S, Hørsholm 18.1 Introduction:the product . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 359 18.2 The quality concept . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 360 18.3 Sensory quality andits measurement . . . . . . . . . . . . . . . . . . . . . . . . . 361 18.4 Appearanceandcolour: measurementanddevelopment . . . . . . 363 18.5 Texture: measurement anddevelopment . . . . . . . . . . . . . . . . . . . . . . 365 18.6 Flavour: measurementanddevelopment. . . . . . . . . . . . . . . . . . . . . . 368 18.7 Taste andaroma:measurementanddevelopment . . . . . . . . . . . . . 372 18.8 The control and improvementof quality . . . . . . . . . . . . . . . . . . . . . 377 18.9 Future trendsin quality development . . . . . . . . . . . . . . . . . . . . . . . . . 381 18.10 References . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 382 19 New techniquesfor analysing raw meat . . . . . . . . . . . . . . . . . . . . . . . 394 A. M. Mullen, TheNational Food Centre, Dublin 19.1 Introduction . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 394 19.2 Defining meatquality . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 394 19.3 Current stateof art techniques . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 397 19.4 Emerging technologies . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 399 19.5 The geneticsof meatquality . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 405 19.6 The future . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 407 19.7 Sources of further informationandadvice . . . . . . . . . . . . . . . . . . . . . 408 19.8 References . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 408 20 Meat packaging . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .

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417 H. M. Walshand J. P. Kerry, University CollegeCork 20.1 Introduction . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 417 20.2 Factorsinfluencing the quality of freshandprocessed meat products . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 419 20.3 Vacuumpackaging . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 424 20.4 Modified atmospherepackaging . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 428 20.5 Bulk, masteror motherpackaging . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 435 20.6 Controlled atmospherepackaging andactive packaging systems . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 437 20.7 Packaging materials usedfor meatproducts . . . . . . . . . . . . . . . . . . . 439 20.8 Futuretrends . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 443 20.9 References . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 444 Index . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 452 x Contents Chapter 1 Professor David Ledward Department of Food Science and Technology The University of Reading Whiteknights Reading RG6 6AP England Tel: +44 (0) 118 9316623 Fax: +44 (0) 118 9310080 E-mail: [email protected] Dr Joseph Kerry and Dr John Kerry Faculty of Food Science and Technology University College Cork, Cork, Ireland Fax: +35 32 12 70 213 E-mail: [email protected] E-mail: [email protected] Chapter 2 Professor Dr Tilman Becker Institute for Agricultural Policy and Marketing University of Hohenheim D-70593 Stuttgart Germany Tel: +711 4592599 Fax: +711 4592601 E-mail: [email protected] Chapter 3 Professor R. K. Miller 2471 TAMU Meat Science Section Department of Animal Science Texas A & M University College Station TX 77843-2471 USA Contributors Tel: 979 845 3935 Fax: 979 845 9454 E-mail: [email protected] Chapter 4 Jennette Higgs Food To Fit PO Box 6057 GreensNorton TowcesterNN12 8GG Northamptonshire England E-mail: [email protected] Dr BredaMulvihil l Glenalappa Moyvane County Kerry Republic of Ireland E-mail: bredamulvihill @hotmail.com Chapter 5 ProfessorFeridoonShahidi University ResearchProfessor Departmentof Biochemistry Memorial University of Newfoundland St John’s NewfoundlandA1B 3X9 Canada Tel: (709) 737 8552 Fax: (709) 737 4000 E-mail: [email protected] Chapter 6 Dr Marianne Jakobsen andAssociate ProfessorGreteBertelsen Departmentof Dairy andFood Science The Royal Veterinary and Agricultural University Rolighedsvej 30 1958FrederiksbergC Denmark Tel: +45 35283268 Tel: +45 35283212 Fax: +45 35283344 Fax: +45 35283190 E-mail: [email protected] E-mail: [email protected] Chapter 7 A.P. Moloney Teagasc GrangeResearchCentre Dunsany County Meath Republic of Ireland Tel: +353 46 25214 Fax: +353 46 26154 E-mail: [email protected] Chapter 8 Dr Margit Dall Aaslyng Danish Meat ResearchInstitute Maglegaardsvej 2 DK-4000 Roskilde Denmark Tel: +45 46303194 Fax: +45 46303132 E-mail: [email protected] xii Contributors Chapter 9 GeoffreyR. Nute Division of FoodAnimal Science Schoolof VeterinaryScience University of Bristol Langford Bristol BS405DU England Tel: +44 (0) 117 928 9305 Fax: +44 (0) 117 928 9324 E-mail: [email protected] Chapter 10 ProfessorH. J. Swatland Department of Food Science Department of Animal andPoultry Science University of Guelph Canada E-mail: [email protected] Chapter 11 Dr PeterMcClure Unilever R&D Colworth Colworth House Sharnbrook Bedford MK44 ICQ England Tel: +44 (0) 1234781781 Fax: +44 (0) 1234222277 E-mail: [email protected] Chapter 12 Dr K. G. Rickert Director of Research Facultyof NaturalResources, AgricultureandVeterinary Science The University of Queensland GattonCampus Gatton Queensland4343 Australia Fax: +61 7 54601324 E-mail: [email protected] Chapter 13 Dr ChristianJames FoodRefrigeration andProcess EngineeringResearch Centre (FRPERC) University of Bristol Churchill Building Langford Bristol BS405DU England Tel: +44 (0) 117 928 9239 Fax: +44 (0) 117 928 9314 E-mail: [email protected] Chapter 14 Dr K. B. MadsenandDr JensUlri ch Nielsen DanishMeat ResearchInstitute Maglegaardsvej2 PO Box 57 DK-4000 Roskilde Denmark Contributors xiii Tel: +45 46303030 Fax: +45 46303132 E-mail: [email protected] Chapter 15 Dr Stephen J. James Food Refrigeration andProcess EngineeringResearchCentre (FRPERC) University of Bristol Churchill Building Langford Bristol BS405DU England Tel: +44 (0) 117 928 9239 Fax: +44 (0) 117 928 9314 E-mail: [email protected] Chapter 16 Dr Marie de Lamballerie-Anton Genie desProcedesAlimentaires ENITIAA BP 82225 44322NantesCedex 3 France Tel: +33 (0) 2 51785465 Fax: +33 (0) 2 51785467 E-mail: [email protected] Dr Joseph Culioli andDr Richard G. Taylor Station de Recherchessur la Viande INRA Theix 63122 SaintGenès-Champanelle France Tel: +33 (0) 4 73624183 Fax: +33 (0) 4 73624089 E-mail: [email protected] Chapter 17 Dr PeterSheard Division of FoodAnimal Science University of Bristol Langford Bristol BS405DU England Tel: +44 (0) 117 928 9240 Fax: +44 (0) 117 928 9324 E-mail: [email protected] Chapter 18 ProfessorDr Ir Daniel Demeyer University of Ghent Departmentof Animal Production Proefhoevestraat10 9090Melle Belgium Tel: +32 9 264 9001 Fax: +32 9 264 9099 E-mail: [email protected] ProfessorLouiseStahnke Meat andFood Safety Chr. HansenA/S BoegeAlli 10–12 PO Box 407 DK-2970 Hørsholm Denmark Tel: +45 45 74 8566 Fax: +45 45 74 8994 E-mail: louise.stahnke@dk. chr-hansen.com xiv Contributors Chapter 19 A. M. Mullen The NationalFoodCentre Teagasc Castleknock Dublin 15 Republic of Ireland Tel: +353 1 8059519 Fax: +353 1 8059550 E-mail: [email protected] Chapter 20 H. M. Walsh Facultyof FoodScienceand Technology University CollegeCork Cork Ireland Fax: +353 21 270213 E-mail: [email protected] Dr JosephKerry Facultyof FoodScienceand Technology University CollegeCork Cork Ireland Fax: +353 21 270213 E-mail: [email protected] Contributors xv Meat has long been a central component of the human diet, both as a food in its own right and as an essential ingredient in many other food products. Its importance has also attracted controversy. Meat consumption has, for example, been associated with chronic diseases such as cancer and heart disease. These and other concerns, such as those over safety, have led to declining consumption of some types of red meat in regions such as the EU. As a result, the questions of what defines meat quality in the minds of consumers, and the ways these quality attributes can be maintained or enhanced during processing, are of particular importance to the food industry. This volume addresses these questions. Chapter 2 provides the foundation for the rest of the book by discussing what defines meat quality. It explores changing consumer perceptions, the cues they use to measure quality attributes, and suggests ways in which the meat industry can meet consumer expectations more effectively. Part 1 considers individual aspects of quality, beginning with a discussion of the factors affecting the quality of raw meat. The nutritional role of meat has been a subject of concern to some consumers. Chapter 4 addresses such concerns and discusses recent research on the nutritional importance of meat in the modern diet. The following chapters consider other aspects of quality such as flavour, colour and the changing fat content of meat. Following on from the discussion in Part 2 of individual quality attributes, Part 3 explores ways in which quality can be measured, beginning with a discussion of how to establish reliable and measurable indicators for quality attributes. Sensory analysis remains essential in both defining and measuring quality, and is reviewed in chapter 9. Whilst the use of trained sensory panels provides the foundation for measuring meat quality, instrumental techniques are essential for effective control during processing. Chapter 10 discusses the range 1 Introduction D. Ledward, The University of Reading, J. Kerry and J. Kerry, University College Cork of on-line instrumentation available, whilst the following chapter considersthe important topic of identifying microbiological hazardsin ensuringmeat safety. The final part of the book looksat a rangeof newtechniquesthat havebeen applied at the variousstagesin the supplychainto provideimprovedandmore consistent quality. The use of computer models to understand and control processesmoreeffectively is growing throughoutthe food industry. Chapter12 looks at its application at the beginning of the supply chain to beef cattle production. The following two chapters then review new developmentsin the subsequent stagesof production, discussing automation in slaughtering and carcasshandling,andthekey areaof carcassdecontaminationafterslaughter. If its safetyandquality areto bepreservedbeforeit is eithersold to theconsumer or goeson for furtherprocessing,raw meatrequireseffectiverefrigeration. The collection thereforeincludes a review of the impact of chill ing andfreezing on meat quality andways of optimising the design andoperation of the meatcold chain. This chapter is complementedby a comprehensive review of current developmentsin meatpackaging. Finally, the book concludeswith chapters on the processing and quality control of such products as restructured meat and fermentedmeatproducts. 2 Meat processing 2.1 Introduction: what is quality? Price and quality are key factors for success in food markets and, as such, are important both for the competitiveness and economic efficiency of firms and of the whole supply chain in meeting consumer demands. The price premium, which high quality products receive compared to low price products, is one measure (in this case financial) of the quality of a product. This price premium is the result of the interplay of the supply of and demand for quality. In terms of the demand side of the market, it represents the marginal willingness of consumers to pay a premium for quality. In terms of the supply side, if markets are competitive, it is equal to the marginal cost of producing a higher quality product. If the supplier is in a monopolistic quality position, prices will be higher than marginal production cost. In general, food markets are rather competitive and price is the predominant parameter of success, but delivering a premium quality may lessen price com- petition and give the supplier the opportunity to increase revenue. In some cases a certain level of quality, defined for example by a farm assurance scheme, may be made a prerequisite by those customers with market power. Products produced according to a premium quality standard as requested by large retailers may gain no price premium but just the opportunity to stay in the market. Food retailers in Great Britain have significant market power (Northen, 2000a, b) compared to the food retailing sector in Germany for example. As a result, some of the price premium for quality paid by the consumer accrues to the large retailers. The members of each stage of the food supply chain (Fig. 2.1) in general and the meat supply chain in particular have their own economic interests and goals. Consumers would like

2.1) in general and the meat supply chain in particular have their own economic interests and goals. Consumers would like to pay low prices whilst retailers prefer high prices for 2 Defining meat quality T. Becker, University of Hohenheim, Stuttgart food products. Retailers would like to purchaseat low pricesin the wholesale food market, while theprocessingindustry tries to maximise its returns. In turn, theprocessorwould like to purchaseraw materials cheaply from theagricultural sector, while farmers try to get the bestprice for their produce. The strategic interests of eachstageof the supply chain are in conflict both with respectto price and,therefore,potentially with respectto quality aswell. Eachstageof the supply chainhasits own definition of quality. Consumers askboth for sensory quality andproducts that aresafeto consume.They may also demanda range of other potential quality attributessuch as nutritional quality which may itself be variously definedto include a rangeof effectson health (such aslevel of fat content).Theymayalsoincludein their definition of quality how a productis manufactured,rangingfrom animalwelfare standards and environmental impactsto product composition and ingredients.Quality is defined by consumers according to their own personal preferencesandgoals. Retailersareinterestedin a high marginandaccordingly in products thatare cheapto purchaseyet cancommand a premium price,areeasyto handle,havea long shelf-life and quick turn-over, and which contribute positively to their image.Price is of utmost importance and quality is defined according to the extent to which a productcontributes to the economicgoals of retailers.Food manufacturers are interested in a high margin and a good product which contributesto their brandimage.The larger manufacturersin particular invest heavily in value-addedproducts which can be usedto createstrongbrands to gain a competitive advantagein the market. A strongindustry brandis not in general in the interest of retailers who prefer to establish their own brands to improve their own marketposition at the expense of food manufacturers. The processingstageitself may include more than one stage. In the meat chain, slaughterhousesareonly thefirst stepin theprocessingof theagricultural product. Furthermore we haveto distinguish hereat leastbetweentwo chains, the fresh meat and the meat product chain. Food processorsare interested in agricultural raw materials in large homogeneous batches producedto quality criteria gearedto thedemandsof manufacturing. Producersusuallysource their raw materials from a number of suppliers. It is often not perceivedto be in the interest of onefarmerto co-ordinateon quality with otherfarmers if thecostof co-ordinationfor the individual farmer is higher thanthe benefit received.This Fig. 2.1 The supplychain for food products. 4 Meat processing will often be the caseevenif the total benefitsof co-ordinationamongfarmers would be muchhigher thanthe total coordinationcost if the latter wasshared between them. Definitions of quality thusdiffer between the different stagesof the supply chainand,asa result,consumerneedsarenot alwaysmet efficiently. In cases where the reputation of manufacturers depends decisively on the quality and safetyof theagriculturalproductsusedasinputs,asin thecaseof babyfood, the industry prescribesfarming production methodsor evenreducesthe role of the farmer to a supplier of land and labour. In creating their own brands,retailers mayalsoimposetheir own quality standardson themanufacturerstheycontract to supply their products and on farmersproducing fresh producefor the retail sector. Contracting of this kind or other forms of vertical integration may preventthe inefficient supplyof quality throughcompetingstagesin thesupply chain, and are a meansof ensuring more uniform quality through the supply chainasa whole. In order to facilitate an efficient supply chain responseto the needsof the consumer, interestsin thesupplychainneedto bealigned. Thereneedsto bean understandingof andcommitmentto meeting theconsumer definition of quality at all stagesof the supplychainfrom retailer throughto the agricultural sector. In the caseof meat this consensusneedsto extendeven further through the supplychainto include, for example, theanimalfeedindustry, andother sectors providing inputsinto agricultural production. An efficient responseof thesupply chain to the consumer demandfor quality implies a communication of quality throughall the stagesof the supply chain.This implies a definition of quality sharedby all the stagesof the supply chainandthe willin gnessof all stagesof thesupplychainto work together to meetconsumerquality demand.This might soundUtopian,but Utopian worlds may give ussigns for the directionto go in the real world. Vertical integration is only one, and sometimes very costly, meansto co-ordinate on quality. Other forms of coordination, like quality standards sharedby all the stagesof the supply chain,might be moreefficient. However, definitionsof quality differ not only between thedifferent stagesof thesupply chain,but alsobetweenthedifferentscientific disciplinesinvolvedin meat quality managementand policy. We will present here a framework for defining quality which is designedto take on board a range of different definitions andwaysof defining quality. This framework requires information distributedamongmanyscientific disciplines.It alsoneedsto takeinto account gapsin knowledgeandsuggests where new researchmight be directed. We will approach the definition of quality by distinguishing between two extremes.Oneview is thatquality mayberegardedasa construct in themind of the customer which is highly subjective and which cannot be measured consistently and objectively. The other extreme view is that quali ty is objectively definedandexistsonly to the extentit is scientifically measurable. Thesubjectiveview is takento theextreme in thefollowing statement: ‘Quality cannotbedefined.It canonly berecognised’.Theobjectiveview is taken to the extremein this statement: ‘Quality existsonly to the extentit canbe measured Defining meatquality 5 with laboratorymethods’. We will not takeeitherof theseextremeviews here. We will regard quality, on the one hand,as a subjectiveconcept since it is dependent on the perceptions, needsand goalsof the individual customer. In some partsof the li teraturefollowing this approachthe term ‘perceivedquality’ is usedto stressthe view that quality is neitherabsolute nor objective.On the other hand,we taketheview thatquality canbedescribedanddefinedevenif it is more thanwhat is measurablewith laboratory methods. While the objective concept of quality is predominant in the supply chain andin the meatsciences, the subjective concept of quality drivesconsumerdemandand is sharedin the marketing andmanagement literature.In our approachboth the subjectiveand the objective quality concept arecombined. We will approachour definition of quality by presenting first the consumer perspectiveandthenthe producer perspective. Thesetwo sections areintended to give a short overview and to lay the ground for the integration of both approaches. The approach, presented in the following section, is basically a combination and, more importantly, an integration of different approaches already available in the literature, which either take the consumeror the producer perspective. 2.2 Consumer perceptionsof quality Sensory studies are frequently usedto evaluate the quality of meatand meat products. According to thesestudies, preferencesfor meatseemto be strongly affectedby colour/appearance andtexture, andto a lesserextentby changes in flavour. Texture may be understoodwith juicinessand tendernessas different dimensions of textural quality (Risvik, 1994). Flavour may be regarded as consisting of taste and smell. However,eatingor sensory quality is only one dimension of consumer perceived quality. Many consumer surveys in several countries of the European Union clearly demonstrate that consumers not only careabouteatingquality but alsoother quality attributessuchasproductsafety (in the light of outbreaks such as BSE and footand-mouth disease),animal welfare, ecological production methods,or thepresenceof residuesor additives suchashormonesor antibiotics usedin animalproduction. There are two main approachesto investigating and modelling consumer behaviour: the consumer studies/marketing approachand the microeconomic approach. In the former, several models are available that seek to capture differentaspectsof consumer attitudesandbehaviour. This approachregardsthe perception of quality as closely linked to the personal goals and endsof each consumer. The means-endchain theory is a good example of this approach. Consumersare assumed to chooseproducts becausethey believethat specific attributes of the product can help them achieve desiredends.Audenaert and Steenkamp(1996)apply this approachto beefandexplain theconsequencesfor marketing beef to consumers in Belgium. Attributes like tender,succulent and the lack of visible fat are linked in the mind of the consumerwith the 6 Meat processing consequenceof anenjoyableeatingexperience,while attributessuchasleanness and the absence of growth-promoting hormonesused in animal rearing are linked to the consequence of a healthy life. Animal welfare, ecological production andotherprocessattributeswereexcludedfrom this analysis. Even with this restricteddesignfocusing exclusivelyon eatingquality, it is clearthat, asidefrom sensory properties,thereexistsat leastoneotherquality dimension in the mind of the consumer, the contribution to a healthy lifestyle. This subjectiveaspectof quality is further pursued in the perceived quality approach. Here quality may be defined as fitness for use, fitness for certain goals, or as the composite of all product attributes which yield consumer satisfaction. Thedistinctionbetween quality cuesandquality attributesbecomes decisive.Quality cuesarewhat theconsumer observes,andquality attributesare whattheconsumerwants.Quality cuesareimportantonly to theextentthatthey actasconsumerperceivedindicatorsfor attributes.Quality cuesmaybeintrinsic or extrinsicto the product. Quality attributesmay be experiencedor haveto be inferred (Steenkamp, 1990). Consumer studies distinguish between quality expectations and quality performance(Steenkampand van Trijp, 1996). At the point of purchasethe consumerformsanimpressionabouttheexpectedproduct quality of alternative food productsand accordingly decides which product to buy. It is generally acknowledged that consumers’ expectations about quality are based on perceptions of quality cues.Quality cues are any informational stimuli that can be ascertainedthroughthe senses prior to consumption, and,according to the consumer, have predictive validity for the product’s quality performance uponconsumption. In the caseof freshmeat, placeof purchaseandcolour are amongthe more important quality cues,as confirmed in Europeanconsumer surveys(Glitsch, 2000a). Thesecuesareessentially subjective. While consumerstudiesliterature stresses the subjective view of quality, economistsanalysingconsumerbehaviourin thecontext of markets,takea view morein accordance with theobjectiveview of quality. Products areregardedas bundlesof objectivelymeasurablecharacteristics.Demand is assumedto depend on incomeandprices(Heienet al., 1996).ChalfantandAlston (1991)stressthe view that changesin meatdemandcanbe explainedusing only relative prices and income variables without assuming a structural change in consumer preferencesor tastes. Davis (1997) discusses the problemsof identifying and measuring structural changein consumer preferences from a microeconomic perspective.

However, economistshavebegunto stressthe importance of non- price/income factors. The non-price/incomefactors which appearto be more important for consumption trendsin the UK, for example, are associated with suchissuesashealthandconvenience(Bansback,1995).AndersonandShugan (1991)stressthesefactorsasthe reasonfor the increasein poultry consumption andthedeclinein beefsales.Von Alvensleben(1995)regardsthecomparatively low productdiversity in the caseof meatas influencingconsumption patterns. Richardson et al., (1993) regardhealth, taste and concerns over additivesas determinantsof changes in meat consumption. Defining meatquality 7 In orderto takeaccount of thedistinctionbetweenthesubjectively perceived quality approachandthe objectivequality approach,we will usethe following terms: • quality attribut es (QA) to denote those quality features of the product perceivedasimportantby the consumer • quality characteristics (QC) to denote those quality features which are scientifically measurable. Food hasto be prepared to become a dish. In order to take this on board,the consumption processitself mayberegardedasa production processwhere food products with otherinputslike time, skill, andothergoodsaretransformedinto the final good which is consumed. Consumer preferencesalso exist for these final goods. These final goods have no market prices but only subjective ‘shadow prices’ in the mind of the consumer (Stigler andBecker, 1977).These final goods become the foundation on which the consumer builds quality attributes. Both the perceived quality approach and the objective quality approacharelinked together if we regardproduct attributesastheoutput of the homeproduction of final goods.The willin gnessto pay a price premium for objectively measurablequality characteristics may be derivedfrom the internal personalvaluationsof quality attributesasvalidatedby thefinal goodsprepared andconsumedwithin the home. The recentfocusof microeconomic theoryon asymmetric information adds other important insights to the consumer perspective on quality. According to Becker (1996), therearethreedecisionframes for theconsumer whenassessing the quality attributesof a product: 1. The decision undercertainty, made at the point of purchase. 2. Thedecisionunderrisk, when theconsumerassumesquality attributeswill be realisedlater at the point of consumption. 3. The decision under uncertainty, where the consumermay not be able to establishthe quality attribute independently. An example of thefirst frame, thedecision undercertainty, is thesizeof a piece of meat. Theconsumercanbesureof thequality attributeby inspection.Wewill denote those attributesas inspection quality attribut es (IQA). Consumersuse other cues, such as the kind of shop or the colour, as inspection quality attributes. Colour, for example, is regardedby consumers as both a quality attribute in itself andevenmoreimportantasan indicatorfor eatingquality and meat safety(Glitsch, 2000b). An example of the secondframe,the decisionunderrisk, is the attribute of meat ‘tenderness’.The consumercannotassessthis attribute when buying the piece of meat,but experiencesthe tendernessonly after preparingthe product and consuming it. Accordingly, we will use the term experience quality attr ibute (EQA) or ‘eating quality’ to denote thosequality attributesthat are experiencedonly in consumption. Consumerslook for certain quality cuesthat suggest the meatwill be tenderto eatafter it is cooked. 8 Meat processing Examples of the third frame, the decision under uncertainty, are ‘animal welfare friendly’ or ‘organic’ production methods.Here the consumerhas in generalnomeansto establishwhether theproduct hasthesequality attributesbut instead hasto rely on third-party information.As anexample, theconsumerhas no way of inferring from the productitself whether the animalhadbeenreared and slaughteredhumanely. As in the caseof experience quality attributes,the consumerhasto rely on cuesbut, in the caseof credence quality attribut es (CQA), trusthasto substitute for personalexperience.Theconsumer is not only interestedin thesensory or eating quality, but alsoin issueslike animalwelfare, environmentally friendly production and,in particular in thecaseof beef, in the safetyof themeat.Thesafetyof a meat product maybeseeneitherasanEQA, sincetheconsumermaybe immediately exposed to anyrisk afterconsumption, or as a CQA if potential health effects are long term. Within the group of credencequality attributeswe will distinguishaccordingly betweenethical and safety/health credencequality attributes. The distinction is important because food safety and health issuesare of importance for the wellbeing of the consumer, while ethical issuesare more important for the well-feeling of the consumer. This asymmetricor incompleteinformation approachshedssomelight on the cue processing process internalised within the consumer. Any content of information, whethercuesor attributes,canbecategorisedaccording to thethree decision frames.Researchshows(Glitsch 2000a,b) that in thecaseof meatand meatproducts, theplaceof purchase,whether butcher’sshopor supermarket,is regardedby consumers (even in those countries where butcher’s shopshave hardlyanyimportance) asa primary indicator, bothof safetyandeatingquality. Priceis regardedasa muchlessimportantindicator. Evenin thosecountrieslike Sweden, where independent butcher’s shops are comparatively rare, their importance as a cue for quality equalsthat of price. Colour and, to a lesser extent,country of origin are, together with place of purchase,also among the first-ranked indicators used by consumers to infer eating quality. In most countriesin Europe, producerlabels andbrands haveonly minor importanceas indicators for quality. Exceptfor beef in Sweden andchickenin Germany, this quality cue is regardedasless importantthanthe place of purchase. Trust is decisive for the consumer in the caseof credencequality attributes. The two most trusted sources of information on the safety of meat in six countries investigated in Europe (Table 2.1) are the independentretailer or butcherandthebutcher in thesupermarket(Glitsch,2000a). Germanconsumers rank consumergroupsin third place,while British and Irish consumers rank their own opinionthird. In thecaseof Swedennewspapers arerankedthird and, in the caseof Italy and Spain, the Department of Health. Italy and Spain, compared to the other countries investigated, are characterisedby a direct involvement of national andregionalministriesin quality policy. Freshness,asindicatedby attributessuchascolour anda juicy texture,seems to be the most important indicator for the safety of meat. Among the more importantexperience-quality attributesrelated to safetyareflavour, tenderness, Defining meatquality 9 Table 2.1 Most trustedsourcesof informationaboutmeat(% of all answers) Germany Ireland Italy Spain SwedenSweden United KingdomUnited Kingdom 1 Independent Butchers in the Independent Independent Independent Butchersin the retailers/butchers supermarket retailers/butchers retailers/butchers retailers/butchers supermarket (37.5%) (36.7%) (28.3%) (25.6%) (10.7%) (23.1%) 2 Butchersin the Independent Butchers in the Butchers in the Butchersin the Independent supermarket retailers/butchers supermarket supermarket supermarket retailers/butchers (6.8 %) (9.8%) (28.2%) (15.1%) (10.2%) (9.3%) 3 Consumer Own opinion Departmentof Department of Newspapers Own opinion groups (4.6 %) Health Health (7.6%) (6.0%) (6.6%) (6.0%) (5.6%) 4 Magazines Reports Friends Consumer Own opinion Newspapers (3.8%) (2.8%) (3.8%) groups (4.6%) (2.9%) (4.7%) 5 Reports Farmer Consumer Own opinion Friends Government (3.7%) representatives groups (4.0%) (4.0%) (2.4%) (2.4%) (3.7%) 6 Friends Newspapers Reports Government Foodsafety Labelling (3.5%) (2.3%) (3.6%) (2.8%) board (2.0%) (3.5%) Source: Glitsch(2000a),p. 139. juiciness and smell. Where possible consumers look for cues for credence quality attributes. Place of purchase, country of origin and, in the caseof chicken, free-rangeproduction have someimportance as cues.Price and the nameof the producer havecomparatively little importance asindicators for the safety of meat. Among the more important safety concerns are the use of hormonesand antibiotics in animal rearing, and the presenceof salmonellain chicken and BSE in the case of beef. Fat and cholesterol seem to be comparatively minor concernsfor Europeanconsumers (Fig. 2.2). This would certainly not hold for consumers in the United Statesof America. From the perspective of the consumer, food shouldbe safe,convenient to prepare,good for the health, tasty and produced in accordance with personal ethical values.The results of consumerinterviewsshowthat, though objective quality may not have changed, the perceivedquality of meat is regardedas havingworsened, though the situation variesbetweencountries (Fig. 2.3). This may be accounted for by changing productattributesdemandedby consumers but not sufficiently taken care of by the supply side. The consumption data showsthat overall meat consumption hasstayedrelatively constantthroughout the last decade. However, while pork consumption and, in particular, poultry consumption hasincreasedfurther,beefconsumption hasdecreased(Fig. 2.4). If quality is defined as fitness for consumption, both consumerinterviews and consumption patternsshowthat the (perceived)quality of beef in particular has decreased overtime. Percapitabeefconsumption in Europehassuffered a longtermdecline,acceleratedmore recentlyby theBSEcrisis.Consumptionpatterns after food scandals recoverafter some time, in mostcases after six monthsor a year.The BSEcrisis is no exception in this regard, but thequality imageof beef Some people think that the quality of food products sold in [our country] is improving,whilst othersthink it is gettingworse.For eachof thefollowing products sold in [our country],pleasetell me if you think its quality is tendingto improveor tendingto get worse? (Showcard.) EU 15 average in % of respondents Tendingto get worse Tendingto improve Neither Freshmeat: 45 32 23 Freshfish: 32 38 31 Freshvegetables: 28 44 28 Freshfruit: 28 46 27 Pre-cookedmeals: 25 43 32 Eggs: 24 39 37 Cannedfoods: 23 38 39 Freshmilk: 21 42 36 Breadandbakeryproducts: 21 49 30 Frozenfoods: 18 49 33 Cheese: 17 48 35 Fig. 2.2 Foodquality perceptionin the EuropeanUnion (February1997).Source: InternationalResearchAssociates(INRA): Eurobarometer47.0,20 March 1997. Defining meatquality 11 hassuffered further damage.Current patterns thus suggest that an increase in overall meatconsumption is very unlikely and that, at best,consumption will remain stable or even decline. Safety is clearly a credencequality attribute which, in the caseof beef in particular, the industry has found it difficult to satisfy. Food preparationshouldbeconvenient.The sizeof householdshasdecreased whilst income hasincreased. As more womenhaveenteredthe labour market, householdshavelesstime to preparemeals. Consumersnow investlesstime and skill in preparing food, and look for convenience foods that require little preparation. Meat is only one ingredient among many in most convenience foods, and has less importance than in a home-mademeal preparation. Consumersurveysclearly showthat the skills required to preparemeatdishes have decreasedfrom generation to generation (Glitsch, 2000a).This loss of domestic culinary skills may

also have reducedthe perceived eating quality attributesof meat,consolidatinga perceived decline in quality. Food shouldbehealthy. Fromtheperspectiveof theconsumer,meat doesnot contribute to healthasmuch asother foodssuchasvegetables.On thecontrary, meat is regardedasa food which may contributeto coronaryheart diseaseand other diseases, andshould thereforebeconsumedless to producea healthydiet (Wildner, 2000). This perception hasagain contributed to a decreasein meat consumption. Food should be producedin accordance with personalvalues. In order to consume meat, animalshaveto beraisedandslaughtered.Consumer attitudes to Some people think that the quality of food products sold in [our country] is improving,whilst othersthink it is gettingworse.For eachof thefollowing products sold in [our country],pleasetell me if you think its quality is tendingto improveor tendingto get worse?(Showcard.) in % of respondents Tendingto get worse Tendingto improve Neither Germany 62 24 14 Greece 60 30 11 Belgium 53 24 23 France 51 29 21 Italy 45 28 27 Portugal 42 40 18 Luxemborg 39 32 29 Denmark 36 35 30 Ireland 35 43 22 Austria 34 37 29 Netherlands 34 38 27 United Kingdom 32 33 35 Finland 29 24 46 Spain 29 54 18 Sweden 25 27 48 Fig. 2.3 Meat quality perceptionin the EuropeanUnion (February1997). Source: InternationalResearchAssociates(INRA): Eurobarometer47.0,20 March 1997. 12 Meat processing Fig. 2.4 Percapitameatconsumptionin the EU. Source:Die Lageder Landwirtschaftin der Gemeinschaft:Bericht/Europa¨ischeKommissionBrüssel1975–1999. Source:ZMP MarktbilanzVieh und Fleisch2001,Eier und Geflügel 2001,Bonn 2001. methodsof production have changedprofoundly. There has been increasing criticism of the useof synthetic additives to enhance quality attributessuchas colour and shelf-life. Consumershave increasingly demandedfoods that are more ‘minimally’ processed and retain their original sensoryand nutritional qualities. In thecaseof meat,therehasbeenincreasingconcern abouttheuseof antibiotics and growth-promoting hormonesto make animal rearing more productive. At the same time consumers have becomemore concernedthat animals are reared,transported andslaughteredin humaneconditions.Finally, there is increasing consumer pressure to make farming practices and manufacturing processes more environmentally friendly. This has been reflected,for example, in the increasing demandfor organic produce. 2.3 Supplier perceptionsof quality As in thecaseof studiesof consumerattitudes,therearetwo distinctapproaches to thetopic of quality from thesupplierperspective:thatof industrial economics andthatof quality management. In microeconomic theory, quality is regardedas a parameter for competition. Firms choosefrom a variety of possiblequality attributesthe bundleof quality characteristics that maximisesprofit. Quality is regarded as only one parameteramong others for competition. The optimal choice of quality depends on the behaviourof the other firms and customer needs(Tirole, 1988). From an economic perspective, firms neednot always meet customer quality needsefficiently, but only to the degreeneededto maintain a profitable position in the market. In particular, in the case of experiencequality attributes, thereexist market equilibrium conditions which mayresultin anundersupply of quality. If consumers preferhigh to low quality and are willing to cover the additionalproduction cost for high quality, there may still be an undersupplyof quality productsif consumersarenot perfectly informedof thequality attributesat thetime of purchaseor haveno reliablecues for judging higher quality. This is well demonstratedby the so-called ‘Lemons Problem’ (Akerlof, 1970). Signals for quality may lessenthe problem of an undersupply of quality. Any reputation mechanism like brands,advertising or warrantiesmay act assucha signal. The focus of the quality managementli teraturehas changed significantly over the last century, shifting first from reactive end-product testingto a more proactive emphasis on improvedprocesscontrol. It hasalso movedfrom a focus on how to produce moreconsistently andmeetspecifications moreexactly to a more consumerorientatedapproachgearedto identifying consumerneedsmore effectively andthendesigningproducts aroundthose needs(Dalen,1996).This quality-by-design approachhasbeendeveloped,for example,in the concept of quality function deployment that requiresa product development teamto find measurablecharacteristics describing customer needs(Akao, 1990). By using the customer’s own rating of importanceof needsandthe specialist knowledge of the relationshipbetween needsand characteristics, it is possibleto find the 14 Meat processing most important characteristics valued by customers and to focus on thesein product design. This is not an easytask: ‘In some instances it is necessary to establish new expressionsto describe the wanted quality. Sometimesnewways of measuringquality must be found. This is one of the challenges to meat research scientistsaswell astheir colleaguesin relatedfields: what to measure in the endproductandhow to measure it’ (Dalen,1996). This approachhas beendevelopedfor industrial designspecifications but falls short in coveringall the peculiarities of food, in particular meat product design.In the caseof meat,bothprocessandproduct attributes,experienceand credencequality attributes,areof importance.Credenceattributesseemto playa dominant role in consumer food demand in general compared to non-food products. The Quality Guidance Approach suggested by Steenkamp and van Trijp (1996) seeksto adapta Quality Function Deployment approach to food product designandcanbe characterisedasfollows: The quality guidancephilosophyconsists of the following steps:(1) measurementof the quality judgementsmade by consumers in the target markets;(2) disentanglement of the quality judgementsinto its constituents, viz. perceptionsof intrinsic quality cuesandquality attributes; (3) linking consumerperceptionswith respect to intrinsic quality cuesandquality attributesto physicalproduct characteristics (Steenkamp andvan Trijp 1996). This addsthe importantdistinction between cuesand attributesto the Quality Function Deployment approach above. Empirical research employing this framework is available for the caseof blade steak.(Steenkampandvan Trijp, 1996). Characteristics measured were colour, fatness, pH, water-binding capacity, shearforce and sarcomere length. Thesecharacteristics were linked to consumer perceptions of freshness, visible fat, appearance, tenderness, flavour, nonmeat components and the quality expectations and quality performanceof the steak.The generalresultsshow that visible fat in the raw steak and perceived tenderness at consumption have relatively accurate counterparts in physical product characteristics. For other consumerquality attributes suchas perceived freshness, presenceof non-meat components and flavour, the conventionally employed physical measures appear to be less effectivepredictors. In most, if not all, countriesof the EuropeanUnion thereare meatquality schemes. Only a few of these cover all the stages of the supply chain. Nevertheless,theseschemesare efforts to co-ordinatequality between at least some stagesof the supply chain. Schemesmay be led by manufacturers, retailers, industry associations or by government agencies. In Ireland, for example,quality schemesarepublicly administered,while those in Spainhavea combination of farmer, industry and publicly administration involvement. In Germany, Sweden and Italy quality schemes are mainly run by farmer organisations/cooperatives. In the United Kingdom, schemesare run by industry-led organisationsand retailers who are able to exerciseconsiderable Defining meatquality 15 influenceover thesupplychain.In general, commercial quality schemesfor the supply chaintendto be run by the channel‘captain’, that is, the mostpowerful player in thesupplychain. In theUnitedKingdom, IrelandandSweden,quality schemes cover most of the supply chain and have a national coverage. In Germany, Italy and Spain quality schemestend to be of regional natureand some of the schemes account for less than 1% of national supply. (Northen, 2000a) 2.4 Combining consumerand supplier perceptions: the quality circle Quality in a marketis the resultof the interplay of demandandsupply. Only if thecostof producinghigh-quality products is less thanthepricereceived will a firm produce highquality products.If firms andconsumersacting in a perfectly competitive market have complete information on quality characteristics, through consumer reliance on measurable inspection quality attributes, the supply of quality productswill be efficient in the sensethat, if the consumeris prepared to pay more than the production cost,productsof the desired quality will besupplied to consumersby themarket.No quality marketfailure occursin this case. However, if we assumemorerealistically thatquality is basedon experience or credencequality attributes, quality is lesseasily defined and measuredby consumers and producers, and there may be a suboptimal supply of quality products. This risk may be lessenedif therearereliable predictive indicators or signals for eating quality suchasbrands or warrantiesthough, aswe haveseen, these are not significant indicators for consumers of meat products. Credence quality attributesdependlargely on trust.In thesecases,claimsby theproducers may haveto be endorsedandregulatedby somekind of reputablethird party. Consumersneedto be convincedboth of the nature andreliability of producer claims andthestanding andeffectivenessof anythird-party regulation(Caswell andMojduszka, 1996). The scientific literaturehascontributed to severalaspects of quality design, production and consumerperception. This chapter is aimed at putting the differentviews together.Theconcept of a ‘circle of quality’ (Fig. 2.5) hasbeen developedto definequality in a manner that takesinto account both consumer andproducerviews on quality andensuresan effective dialogueandconsensus in themarket.Current research on quality hastendedto neglect theproblems of communication between consumers andproducersin definingwhateachmeans by quality. Clearly, communication is very importantin the caseof experience quality attributesandevenmore so in the caseof credencequality attributes. While the circle of quality is intended to give a frame for consumer- orientatedmeatquality management,theframehasto befilled by therespective experts. Researchers respectively in meatscienceandquality managementhave to come together with those analysing consumer behaviour and the 16 Meat processing microeconomic behaviour of firms to develop robust quality management schemes. The circle of quality is intended to clarify the approachesusedin the differentdisciplinesandto contributeto acommonunderstanding. It is clearthat focusingon inspectionquality attributes,suchas the appearanceof meat,and even experience quality attributes, that is the eating quality of meat,may be inadequate if this meansneglecting consumer demandsfor credence quality attributes. It also becomes clear that quality production is only one part of quality managementandneedsto be matchedby an equalemphasis on understanding how consumers assessquality andeffectivequality communication to the consumer. The assumptions underlying

the quality circle have beenreviewed in the previoustwo sections. On the one side there is the consumerwith her or his perception of quality basedon both product and process.This perception is basedon quality attributes, which are assessedby inspection, experience or credence. Cues are used by the consumer as indicators to infer quality, in particular for experienceor credencequality attributes.Theconsumersideof the quality circle is only oneside, thedemandside.Theothersideis theproduction sideof quality. Thewholesupply chainis regardedasoneproducer to keepthe Fig. 2.5 The quality circle. Defining meatquality 17 exposition simple.Problemsaccruing from thedifferent interestsof thedifferent stagesof the supplychainhavealreadybeendiscussed in the beginning of this chapter. Quality managementincludes both the designof the productand the processto meet consumers’ needs.While quality characteristics mayneedto be expressedastechnical specifications, thesecharacteristicshaveto be translated into signals, like brands, labels, advertising and other information to be communicatedto theconsumer. Theproducer maybeableto control thesignals for productcharacteristics,like thebrandimage,but not all thecuesusedby the consumer to infer quality attributes.Here the communicationprocessitself is decisive. Accordingly, we needto distinguish not only betweenattributesand characteristics, but also between signals from the producer and cues for the consumer as indicators for quality attributes. Attributes and characteristics, signals and cues are regarded here as the constituents of the universeof a consumer-orientatedquality management.Thefull quality circle consists of two parts,the production andthe communication part. The production part of the circle needs to bridge the gap between characteristics and attributes.There is now a significant body of research,for example, on theeffectsof breed, feeding, rearing,transportingandslaughtering (Chapter 3) and chill ing (Chapter15) on raw meatquality. Researchhasalso improved understanding in such areasas the control of colour and flavour (Chapters5 and6), andthereare increasingly sophisticatedwaysof measuring these characteristics (Chapter 10). Meat and meat product producerstherefore haveincreasingly sophisticatedmeansof measuring inspection andexperience quality characteristics. Improvements in consumer and sensory research (Chapter 9) have helped to show how these characteristics correlate with attributesperceivedby the consumer. However, eating or experience quality is only one category of quality characteristics. Hardly any informationon the ‘production’ of credencequality characteristicsor thelink of thesecharacteristics to attributesis available.As we haveseen,consumer research hasmade importantadvancesin identifying these attributesand the cuesusedby consumers to assessthem. Consumersurveys clearly showthat credencequality attributeshavegained in importance for the consumer in judging the quality of meatandmeat products. Thoughwe know from consumersurveys which credencequality attributes are perceived as important,we hardly know how to defineproduct andprocesscharacteristics to meet theseconsumer demands,or to matchsignalsto the cuescustomers look for in assessingtheseattributes. Communication is of particular importance for experience and credence quality attributes.In thecaseof credencequality attributes,trusthasto substitute for personal experience. Though there may be product and process characteristics available to meet consumer demandsfor credence quality attributes, unless they are defined, enshrined in technical regulations and efficiently communicatedto theconsumer,a quality problemoccurs.Thewhole circle consists of both the management of quality production and of quality communication to the consumer. Both the productionandcommunication parts 18 Meat processing haveto beaddedto createthefull quality circle.Without bothparts,thecircle is incomplete. The quality production circle starts from the characteristics and links theseto attributes.The quality communication circle starts with these characteristics,identifies cuesand corresponding signals to turn them into the quality attributesthat the consumeris looking for. Quality communication is of particular importance in the caseof process characteristics.Technical regulations may define product and processquality characteristicsin detail,but haveto becommunicated to theconsumer usingthe right signals, particularly in the caseof processcharacteristicsextrinsic to the product. Thesignalsareintendedby thesenderof thesignal, theproducer, to act as indicators for product and processquality characteristics but have to be received and interpreted by the respective consumer as cues.Someof these signalsmay act as cuesfor the consumer, othersmay be ineffective. Some of thesesignalsmay communicate to the consumerwhat the produceroriginally intended. Other signals may even be interpreted in a way contrary to the meaning intended. Only those cueswhich are trustedand acceptedas reliable indicators by the consumer have some influence on consumerattitudes and behaviour. Those that are not may even deepenconsumermistrust. The perception of credence quality attributes, l ike animal welfare friendly production, is particularly sensitiveto the degreeof trust in the information source.The claim of a producer that production is welfare friendly, is not a direct verifiable signal unless,for example, it is validated by a reputable third party in which the consumer hastrust. Our approach has demonstrated that, for credence quality attributes in particular, unresolvedissuesin communicating qualityhinder anefficient supply of quality in themarket.Ethicalandsafety/health issueshaveto beproducedand communicated. Without trustedindicators and signalsconsumerneedsare not fulfilled. Both public and private quality managementschemesin the meat sectorcould be improved to meetconsumerneedsby taking more into account the communication element in quality management. 2.5 Regulatory definitions of quality Quality standardsfor meat, as laid down in mandatorypublic quality schemes are predominantly targeted towards food safety and hygiene, though they do covereatingquality, animalwelfare andotherethical issues. 2.5.1 Standards for food hygiene and safety The generalrules for food hygiene in the European Union are laid down in Directive93/43/EEC. Thisdirectivelaysdowngeneralrulesfor hygienecontrol, covering meat processing though not primary production. Food hygiene is definedas ‘all measuresnecessary to ensurethe safetyand wholesomenessof foodstuffs’. TheHACCP systemis made mandatory.MemberStatesareableto Defining meatquality 19 maintain or introduce national hygiene provisionsthat are more specific than those laid down in theDirective, providing that thesearenot lessstringent,and thattheydonotconstituteabarrier to tradein foodstuffs producedin accordance with the Directive. While the exclusion of primary production from product liability hassubsequentlybeenabolished,theintroductionof HACCPsystemsin the agricultural sectoris still limit ed,althoughmany microbiological problems havetheir sourcein the agricultural sector,suchassalmonellain chicken.The White Paperon FoodSafety(Commissionof theEuropeanCommunities,2000) hasannounced that: A new comprehensive Regulation will be proposedrecasting the existing legal requirements to introduce consistencyandclarity throughoutthe food production chain.The guiding principle throughout will be that food operators bearfull responsibility for the safety of the food they produce.The implementation of hazardanalysisandcontrol principlesandthe observanceof hygiene rules,to be applied at all levels of the food chain,mustensurethis safety. Within the overall framework of general hygieneregulation, more than 20 Directivescoverdifferentaspects of meathygiene.As a result of theBSEcrisis in particular, these Directives have been supplemented by more than 30 Decisions of the European Commission. As an example, Regulation2377/90/ EEC lays down procedures for establishing maximum residue limit s for veterinary medicinal products in foods of animal origin. Maximum allowable residue-levels of veterinary medical productsaredefinedin Regulation675/92/ EECandsubsequentregulations.Regulation 315/93/EECdefinescontaminants, howtheyshould behandled(through,for exampleGoodManufacturingPractice (GMP)) and,whereappropriate, maximum allowablelevels.Directive 86/363/ EEC specifiesmaximum levelsfor pesticideresidues in foodsof animalorigin. The BSE crisis hasresultedin a significant extensionin food safetyregulation. The establishing of a systemfor the identification and registration of bovine animals (Regulation 1760/2000/EU) would probably not havebeenpolitically feasible without the BSE crisis. Though a systemfor beef traceability was introduced mainly to meetsafety considerations,it also underpinslabelling of meat products, an areacoveredby other legislation governing quality. 2.5.2 Standards for animal welfare and other ethical issues The first EuropeanUnion legislation on animalwelfare wasintroducedin 1974 (Directive 74/577/EEC), laying down requirementsfor the stunning of animals before slaughter.Sincethat time a wide body of animalwelfare legislation has been introduced. The Treaty of Maastricht included a declaration on the protectionof animalswhich called for EU member statesto takeproper account of the welfare requirements of animals when drafting and implementing legislation. Specific welfare standards havealsobeenlaid down for individual species. Regulation 1804/99 extendsthe Regulation for organic production 20 Meat processing (2092/91) to cover animal production. These Regulations define the requirementsfor the productionprocessof productsto be labelled as organic. Standardsfor organic productionmethodscan be regarded as combining both environmentalandanimalwelfare standards.Theseregulationsalsocoverother ethical and safety issues,like restrictions on the use of genetically modified organisms in agricultural production.These standards can be categorised as regulating a wide rangeof ethical credencequality attributes. 2.5.3 Standards for eating quality Compulsory carcassclassification for cattle and pigs was implementedunder Regulation 1208/81 andRegulation3220/84respectively.The main aim of this systemwas to referencethe processing quality of carcasses for standardising price reportingsystems acrossmemberstates. This carcassclassification canbe regardedas providing an internal quality standard for the meat trade and, becauseit is not communicated to theconsumer, hasonly an indirect impacton eatingquality. The European Quality Beef Schemeis an effort to establisha quality label for fresh beef directedspecifically at the consumer. So far, the successof this schemeseemsto be ratherlimited (Becker,2000) 2.6 Improving meat and meat product quality A prerequisite for the improvement of (perceived)meat and meat product quality is a common understanding of quality betweenthe consumerand the producer. In particular, communication to the consumer of quality attributes seemsto be the weakestpart of quality management in the

meat sector. Communication is a two-way concept and implies listening to the needsand perceptions of the consumerand informing the consumer effectively about quality attributesin a way that is meaningful to theconsumer.Thesupply chain hasto listenandto speakto theconsumermorecarefully thanit hasdonesofar. Quality attributesperceivedasimportantby theconsumer havebeendivided into three categories: inspection, experience and credence attributes. Of particular importance for meat and meat products are credence attributes. Within this category we havedistinguishedbetween ethical and safety/health attributes.The managementof inspectionquality attributesandthe appearance of meat in the shop needsstill further improvement, but we will focus on experiencequality attributesandon credencequality attributes. 2.6.1 Experience quality attribut es Eating quality could be improved further by integrating sensoryresearch with research in meat science. In an ideal world from the quality management perspective, research should start with consumer perceptions of important attributesandinvestigateprofitable ways of producing the productandprocess Defining meatquality 21 characteristics linked to thesequality attributes.Theeatingquality of meatis the result of the home production process of the consumer. An efficient quality managementprogrammehasto includethis stageof processing.Consumerskills in preparingmeat and knowledge of meat recipeshave decreased over time, contributing to the decline in meat consumption. Product development and innovationin themeat sectorshouldtakemoreinto accountthegrowing demand of consumers for conveniencein preparation. Consumersuserelatively few predictive cuesto judge the eatingquality of meat. The placeof purchase,whether butcher’sshopor supermarket,and the colour providethemaincuesindicatingeatingquality. This clearly demonstrates that more predictive indicators, from an objective point of view, are needed. There is nothing like a quality gradeor quality classificationscheme available for consumers in the caseof freshmeat. Evenmore important,predictive cues alreadyavailable, like ageandsexof theanimals,andwhattheanimalis fed on, are not communicatedto the consumer.In the caseof fresh meat,brands and labels play hardly any role ascuesto indicateeating quality. Efforts shouldbe made to give consumers better and fuller predictive cues to indicate eating quality, for example by developing andestablishing a sensory quality indexand communicating this index to the consumer. In the fish sector, efforts have alreadybeenmade to establish sucha quality index. 2.6.2 Credencequality attribut es In comparisonwith theUS,meatin theEU seemsto havea betterhealthimage, in particular with respectto cholesterol. Thereneedsto be further improvement in the healthimageof meat(seeChapter 4). Improvementsin communication seemto bemorepromising in increasingperceivedquality thanimprovementsin production which are alreadysignificant. The BSE crisis hasundermined the safety imageof meat. Public policy hastakenoverthetaskof meeting consumer demandsfor food safetyby, for example, establishing traceability systemsfor meat. Therecentstabilisation of beefconsumptionandthelack of mediainterest in further BSE casesseem to indicate that public policy has been quite successful in this respect. However,other safety concerns suchas the useof antibiotics in animalrearingarestill significantandneedto betaken account of by both the industry andgovernment.The focusof public mandatorystandards has traditionally been on the management and control of safety. Private standards,as laid down in quality schemes, havebeentargeted more towards eating quality and ethical credencequality attributes.However, progresshas sometimesbeenpiecemealwith pricecompetition, for example,putting pressure on the implementation of more expensive animal welfare standards in production. Public standardsare increasingly taking over the task of defining technical regulations for ethical credenceattributesaswell. 22 Meat processing 2.7 References AKAO, Y. (1990): Quality Function Deployment.Productivity Press: Portland, 1990. AKERLOF, G. (1970): The Market for ‘Lemons’: Quality Uncertainty and the Market Mechanism. In: Quarterly Journal of Economics, Vol. 84, pp. 488–500. ALVENSLEBEN, R. VON (1995): Die Imageproblemebei Fleisch. Ursachen und Konsequenzen.In: Berichte über Landwirtschaft, Vol. 73, pp. 65–82. ANDERSON,E. and S. SHUGAN (1991): Repositioning for Changing Preferences: TheCaseof BeefversusPoultry.In: Journalof Consumer Research, Vol. 18, pp. 219–232. AUDENAERT,A. andJ.B.STEENKAMP (1996):Exploring theNatureof Consumer’s Cognitive Structuresfor Beef. In: Agricultural Marketing and Consumer Behaviorin a Changing World. Wageningen,1996,pp. 81–89. BANSBACK, B. (1995): Towards a Broader Understanding of Meat Demand Presidential Address.In: Journal of Agricultural Economics, Vol. 46, pp. 287–308. BECKER, T. (1996):Quality Policy andConsumer Behaviour.In: Schiefer,G. and R. Helbig (eds): Quality Management and Process Improvement for Competitive Advantagein Agriculture and Food. Volume I. Proceedings of the 49th Seminar of the European Association of Agricultural Economists (EAAE), February 19–21, 1997, Bonn, Germany. Bonn 1997,pp. 7–28. BECKER, T. (2000): EU Policy Regulating Meat Quality. In: Becker, T. (ed.) Quality Policy and ConsumerBehaviour in the European Union. Kiel: Wissenschaftsverlag Vauk, 2000,pp. 53–72. CASWELL, J. and E. MOJDUSZKA (1996): Using Informational Labeling to Influence the Market for Quality in Food Products. In: American Journal of Agricultural Economics, Vol. 78, No. 5, pp. 1248–1253. CHALFANT, J. and J. ALSTON (1991): Accounting for Changesin Tastes. In: Journal of Political Economy, Vol. 96, No. 2, pp. 391–410. COMMISSION OF THE EUROPEAN COMMUNITIES (2000): White Paper on Food Safety.Brussels, 12. January 2000. DALEN, A. (1996): AssuringEating Quality of Meat. In: Meat Science, Vol. 43, No. S, S21–S33. DAVIS, G. (1997): The Logic of TestingStructural Changein Meat Demand: A Methodological Analysis and Appraisal. In: American Journal of Agricultural Economics, Vol. 79, pp. 1186–1192. GLITSCH, K. (2000a): Consumer Requirements for FreshMeat: Resultsof the Survey. In: Becker,T. (ed.) Quality Policy and Consumer Behaviour in theEuropeanUnion.Kiel: WissenschaftsverlagVauk, 2000,pp.113–156. GLITSCH, K. (2000b): Consumer Perceptionsof Fresh Meat Quality: Cross- NationalComparison.In: British Food Journal, Vol. 102,No. 3, pp.177– 194. Defining meatquality 23 HEIEN, D., T.-N. CHEN, X.-L. CHIEN and A. GARRIDO (1996): Empirical Models of Meat Demand: How Do They Fit Out of Sample?In: Agribusiness, Vol. 12, No. 1, pp. 51–66. NORTHEN, J. (2000a): Quality Attributes and Quali ty Cues. Effective Communicationin the UK Meat SupplyChain.In: British Food Journal, Vol. 102,No. 3, pp. 230–245. NORTHEN,J. (2000b): PrivateInitiativesto ManageSafetyandQuality of Meatin SelectedMemberStatesof theEU. In: Becker, T. (ed.)Quality Policy and ConsumerBehaviourin the European Union. Kiel: Wissenschaftsverlag Vauk, 2000,pp. 193–220. RICHARDSON, N., H. MACFIE and R. SHEPHERD (1993): Consumer Attitudes to Meat Eating. In: Meat Science, Vol. 36, pp. 57–65. RISVIK, E. (1994): SensoryPropertiesandPreferences.In: MeatScience, Vol. 36, pp. 67–77. STEENKAMP, J.-B. (1990): ConceptualModel of the Quality PerceptionProcess. In: Journal of BusinessResearch, Vol. 21, pp. 309–333. STEENKAMP, J.-B. andH. VAN TRIJP(1996):Quality guidance:A Consumer-Based Approach to FoodQuality Improvement using Partial LeastSquares.In: European Review of Agricultural Economics, Vol. 23,No. 2, pp.195–215. STIGLER,G. andG. BECKER (1977): De Gustibus Non Est Disputandum.In: The American EconomicReview, Vol. 67, No. 2, pp. 77–90. TIROLE, J. (1988): Thetheoryof industrial organization.MIT Press:Cambridge 1988. WILDNER, S. (2000):Die NachfragenachNahrungsmitteln in Deutschlandunter besonderer Berücksichtigung von Gesundhei tsinformationen. In: Agrarwirtschaft, Zeitschrift für Betriebswirtschaft, Marktforschung und Agrarpolitik , specialissueno. 169. 24 Meat processing Part I Analysing meat quality 3.1 Introduction Establishing an understanding of raw meat eating quality and consistency is an important component of meat production systems. It is generally understood that production of meat must be tied to the production of a product that consumers find visually appealing, that they will continually purchase and that consistently delivers an acceptable eating experience. Therefore, meat quality encompasses the visual appearance and eating quality. Both of these quality factors can be influenced by ante-mortem and post-mortem production factors. This chapter will concentrate on ante-mortem production factors of breed and genetic effects, dietary influences, and rearing effects on meat quality and the post-mortem factor of the slaughter effect will be discussed as a post-mortem production factor. This information will provide a basis of understanding for subsequent discussions on meat quality in ensuing chapters. 3.2 Quality, meat composition and structure Meat is composed of lean tissue or muscle fiber cells, fat and connective tissue. Fat or adipose cells can be found in up to three depots or locations in meat. Fat can be deposited intramuscularly as marbling or contained between muscles (defined as seam fat) or it can be found as external fat or subcutaneous fat. Additionally, meat may include bone, but the trend has moved toward boneless meat cuts and therefore bone will not be discussed in this chapter. Nervous tissue and components of the blood system are contained within meat but their total weight or proportional contribution to meat is small and so will not be 3 Factors affecting the quality of raw meat R. K. Miller, Texas A & M University, College Station discussed.Thesethreemajor componentsof meat,fat, leanor the myofibrillar component,andconnective tissue,affect meatquality in different ways. 3.2.1 Fat component Intramuscular fat content hasbeenshownto affect flavor, juiciness, tenderness and visual characteristics of meat. Savell and Cross (1988) developed the Window of Acceptability to demonstrate the generalrelationship between the roleof increasedintramuscularfat onmeat pork, lambandbeefpalatability (Fig. 3.1). In general, as fat content increases, palatability increases;however, improvements in palatability with increasing fat percentagearenot equalacross all fatnesslevels. If fat contentis lessthan3%, palatability decreasesmarkedly with eachdecreasein fat percentage.In fact, this is the steepest slopeon the curve. As fat increasesfrom 3%to about6%,meat palatability improves,butnot asdramatically asreportedat the lower levels.As fat contentexceeds7.3%,fat is highly visible and has been identified as too fatty by health-conscious consumers.Too muchvisible fat hasraisedquestionsaboutconsumption of fat in meat productsand increasedincidence of coronaryheart disease, obesityor some formsof cancerin humans; these issuescanaffect consumers’ perception of acceptability. Therefore, meat with fat content between3 and 7.3% is generally considered acceptable. Diet/health-conscious consumers may be willin g to sacrifice palatability for lower fat content. How does intramuscular fat affect palatability? One way is through the relationship of intramuscular fat with meat juiciness.As intramuscular fat increases,humansperceivethatthemeatis juicier. During

mastication or during the first bites,if fat is present,someof it is releasedandthesalivaryglandsare stimulated.This resultsin a perception of juiciness,additionally, meatwith a Fig. 3.1 TheWindowof acceptability.Adaptedwith permissionfrom DesigningFoods: AnimalProductOptionsin theMarketplace.Copyright1988by theNationalAcademyof Sciences.Courtesyof the NationalAcademyPress,Washington,DC. 28 Meat processing higher fat contentmay give a longer sustained perception of juiciness.Savell andCross(1988)stated that ‘fat may affect juicinessby enhancing the water- holding capacity of meat, by lubricating the muscle fibers during cooking,by increasing thetendernessof meat andthustheapparentsensation of juiciness, or by stimulating salivary flow during mastication’. A second way that intramuscular fat affects palatability is through the relationship between fat content and tenderness. Interestingly, there is conflicting evidenceas to the meattendernessand fat relationship. Savell and Cross(1988)supportedtherelationshipbetween increasedintramuscular fat and meat tendernessby proposing four hypotheses. The first hypothesis,the Bulk DensityTheory,statesthatasfat is lower in densitythanheat-denaturedprotein in cookedmeat,asthe fat percentageincreases,the overall densityof the meat decreases. As bulk densitydecreases within a given bite of meat,the meat is more tender. The second hypothesis is defined as the Lubrication Effect. Intramuscular fat is mainly triglyceridesstoredin adiposecellsembeddedin the perimysial connective tissuewall of themuscle.As meatis cooked, triglycerides melt and bathe the muscle fibers. As the meat is chewed, fat is released, salivation increasesandthemeatis perceivedasjuicy. Additionally, themuscle fibers give or slide more easily resulting in an increased perception of tenderness.The third hypothesis,the InsuranceTheory, statesthat fat provides protection againstthe negative effectsof overcooking or high heaton protein denaturation. Meatproteinsareinvolvedin bindingwaterin themusclefiber.As meatis cooked,proteins denatureand losesomeof their ability to bind water. Fatcanact to insulatethe transfer of heator slow downtheheattransfer sothat protein denaturationis lesssevere andlessmoisture is lost during cooking. The fourth theory or the Strain Theory relatesto the weakeningof the perimysial connective tissue surrounding muscle bundles. As marbling is deposited as adiposecells dispersedin perimysial connective tissue,development and an increased number of adipose cells weaken the connective tissue structure resultingin moretender meat. To understandif marbling or intramuscular fat affectedconsumeracceptance and the subsequent relationship with trained sensory responses, the Beef CustomerSatisfactionstudywasconducted(Lorenzenet al., 1999; Neelyet al., 1998; Savell et al., 1999) in the United States.Beef top loin steaksfrom four USDA Quality Gradeclassifications were selected to represent four Quality GradeclassificationswhereLow Select would containbeeftop loin steakswith Slight00 to Slight50 degrees of marbling that would equate to about3 to 3.5% chemical lipid; High SelectsteakshadSlight51 to Slight100 degreesof marbling or about3.5 to 4.0% chemicallipid; Low Choicesteakshada small degreeof marbling or about4 to 5% chemical lipid; andTop Choice consistedof steaks with modestandmoderatedegreesof marbling or about6 to 7% chemical lipid. Chemical lipid approximationswere projectedfrom Savell and Cross (1988). Steakswere evaluatedby 300 householdsin four citieswhere eachhousehold containedtwo adultconsumers who atebeefthreeor moretimes perweek. Four top loin steaksfrom eachcarcasswasservedto four consumers in eachcity and Factors affecting the quality of raw meat 29 one steak was evaluated by a trained meat descriptive attribute panel and Warner-Braztler shearforce was conducted as a mechanical measurementof tendernessasdescribed by AMSA (1995). ConsumersratedTop Choicesteaks highest for overall like andjuiciness(Table3.1).They liked the tendernessand flavor of Choice(Top ChoiceandLow Choice) steakscomparedto Select steaks and they indicatedthat the Choicesteakshada higher intensity of flavor than Select steaks.Trained sensorypanelsalso indicated that as marbling score increased,cookedbeeftop loin steakswerejuicier,moretender,moreintensein flavor andthey hadhigher levelsof beefflavor andbeeffat flavor (Table 3.1). Warner-Bratzler shear force values decreasedas marbling score increased (Table 3.1). In this samestudy, top sirloin and top round steaksalso were evaluated.Thesesteakshadslightly lower fat contentthan top loin steaksand the marbling to palatability relationship wasnot asstrong. In pork,a similar study wasconducted in threecitieswith pork consumers in theUnited States.Porkloin chopswere selectedto vary in pH, lipid contentand tendernessasdeterminedby WarnerBratzlershearforcevalue (Table3.2).Pork consumers in the US did not rate pork loin chopsdifferently basedon lipid content.However,when asimilar studywasconductedwith Japaneseconsumers (Table3.3),Japaneseconsumersratedpork loin chopswith higherNationalPork Producer Council (NPPC) marbling score(NPPC marbling scoresare a visual assessmentof intramuscularfat andtheyarerelatedto a chemical lipid value)as juicier, they liked the flavor and taste,they liked the color and they tendedto like the amountof fat andvisual appearance. Pork loin chopswith the highest level of lipid tendednot to bepreferredby Japaneseconsumersmostlikely due to too much visible fat. In summary,there is a marbling to meatpalatability relationship, but this relationship may vary across meat speciesand across consumer populations.While this relationship is not strong acrossall meat species,increased marbling or intramuscularfat assistsin improving the eating quality of meat. Intramuscular fat also has an indirect relationship to meat tenderness.As animals grow anddevelop,fat is depositedsequentially andmarbling is the last fat depot to fill. Marbling therefore is an indication of growth and nutritional status of animals.If animalsarefed high-energy-baseddietsthey grow rapidly or they havehigh ratesof protein andlipid accretion.The endresult is heavier animals with higher levels of subcutaneous,seamand intramuscular fat and greater musclemass.Theseheavier, fatter and more muscular carcasseschill slower and are less susceptible to coldinducedtoughening (seediscussionin 3.2.2). Additionally, animals fed energy-based diets, that grow rapidly have higher collagen solubility (see discussion in 3.2.3) that improves meat tenderness.It becomesapparentthat interrelationshipsbetween the connective tissue, muscle fiber and fat componentare involved in understanding meat palatability. Marbling hasbeenshown to affect consumerandtrained sensorypanelmeat flavor attributes(Tables3.1,3.2,3.3).As fat level increases,consumers tendto like the flavor of beef and pork. Fat hasa characteristic flavor and hasbeen 30 Meat processing Table 3.1 Least squaresmeansof top loin steaksfrom US Beef CustomerSatisfactionStudy for consumersensoryattributes,a trained meat descriptivesensoryattributesandWarner-Bratzlershearforce (kg) aseffectedby USDA quality grade USDA quality grade Root mean Quality attribute Top choice Low choice High select Low select squareerror P-value Consumersensoryattributesa Overall like/dislike 19.2c 19.1c 18.8c 18.7c 3.06 0.0004 Juiciness 18.5c 18.5c 18.3d 18.0c 3.57 0.0006 Tendernesslike/dislike 19.0cd 19.2d 18.6cd 18.6c 3.28 0.0001 Flavor intensity 19.1c 19.2d 18.9cd 18.9c 2.87 0.0009 Flavor like/dislike 19.3cd 19.3d 19.0cd 18.9c 2.88 0.0002 Trainedmeatdescriptivesensoryattributeb Juiciness 5.8d 5.6c 5.5c 5.4c 0.58 0.0001 Muscle fiber tenderness 6.7d 6.6cd 6.5c 6.5c 0.58 0.01 Connectivetissueamount 6.8c 6.9d 6.9c 6.9c 0.45 0.55 Overall tenderness 6.6d 6.6cd 6.5c 6.5c 0.56 0.06 Flavor intensity 5.7d 5.7d 5.6c 5.6c 0.31 0.002 Beef flavor intensity 3.5d 3.5d 3.3c 3.3c 0.32 0.0001 Beef fat flavor intensity 2.1e 2.0d 1.8c 1.8c 0.23 0.000a Mechanicaltendernessmeasurementb Warner-Bratzlershearforce, kg 2.70d 2.75d 3.00c 2.95c 0.71 0.0002 a Valuesfrom Neely et al. (1998) andLorenzen et al. (1999). Valuesdiffer from thosereportedasmodelsdiffered slightly in order to generate theseleastsquares means. Consumers’ sensoryattributeswere rated as1= dislike extremely, not at all juicy, not at all tender, dislike extremely, andno flavor at all, respectively and 23= like extremely, extremely tender,extremely juicy, like extremely, and an extreme amountof flavor, respectively. b Valuesareunpublisheddata,but they werederivedfrom the samedatasetaspublishedby Neely et al. (1998) andLorenzen et al. (1999). cde Leastsquaresmeanswithin a row anda cut lacking a commonsuperscript differ (P identified asoneof the major components of the meatflavor lexicon (Johnsen andCiville, 1986).Whereasfat is not thepredominantflavor in meat,it provides a balancebetween leanandfat flavors. Whenmeatcontainsvery low levelsof fat, the predominant flavors are thoseassociated with the lean suchascooked beef lean,serumy, bloody,grainy, metallic, livery/organy,andbrothy (Johnsen and Civille, 1986; Lyon, 1987). As the level of fat or marbling increases, the cookedfat aromaticor flavor increases in meatand this aromatic canassistin decreasingor masking flavor attributesassociatedwith lean, providingabalance of flavors. 3.2.2 Lean or muscle fiber component The major componentof meat is leanand lean is mainly composedof muscle fibers. Muscle fibers from the cellular structure that possessesthe contractile apparatusof themuscle. Muscle proteinsalsoarethecomponentsin themuscle fiber that bindswateror interacts with waterto hold it in the muscle fiber. The structural integrity and the ability of the muscleproteins to bind water affect meat tendernessandjuiciness. Therearetwo components of the musclefiber structure, the contractile state andthedegradativestate,thatinfluencemeattenderness.In li ving tissue, muscle Table 3.2 Least squaresmeans for pork consumersensory traitsa as affected by predeterminedcategoriesof lipid, Warner-Bratzlershearforce, andpH from loin chops from the US Pork ConsumerSensoryStudy.Adaptedfrom Miller et al. (2000). Trait n Juiciness Tenderness Flavor Overall like pH category 0.04 0.0165 0.06 0.03 Low 648 3.3d 3.3d 3.2 3.2d Medium 620 3.3d 3.3d 3.2 3.2d High 498 3.5e 3.4e 3.4 3.4e RSDc 1.13 1.08 1.10 1.03 Lipid category 0.20 0.19 0.09 0.18 Low 427 3.4 3.3 3.3 3.2 Medium 857 3.3 3.3 3.2 3.2 High 482 3.4 3.4 3.4 3.3 RSDc 1.3 1.08 1.05 1.03 Shearcategory 0.0004 0.0001 0.0004 0.0001 High 379 3.2d 3.1d 3.1d 3.0d Medium 844 3.4d 3.3e 3.3e 3.3e Low 520 3.5e 3.5f 3.4e 3.4e RSDc 1.12 1.07 1.05 1.03 a Consumerattributeswere evaluatedusing a 5-point hedonic,end-anchored sensoryscalewhere 1= dislike extremelyand5= like extremely. b P-valuefrom the Analysisof Variancetable. c RSD= ResidualStandardDeviationfrom the Analysisof Variancetable. def Leastsquaresmeanswithin a columnanda trait lackinga commonsuperscriptdiffer (P Table 3.3 Least squaresmeansfor consumersensoryscoresof pork loin chopsfrom the JapanesePork ConsumerStudy that vary by NPPC marblingscoresdeterminedat the 10th rib in the Longissimusmuscle.Adaptedfrom Miller et al. (2000) Marbling scorec Consumerattribute 1 2 3 4 5 6 P Value Aroma like/dislikea 3.20 3.11 3.16 3.27 3.87 3.00 0.13 Juicinesslike/dislikea

3.09de 3.00d 3.01de 3.13de 4.12e 3.36de 0.048 Tendernesslike/dislikea 3.34 3.29 3.25 3.39 4.25 3.82 0.07 Flavor like/dislikea 3.15d 3.19d 3.14d 3.29d 4.12e 3.64de 0.04 Overall tastelike/dislikea 3.15d 3.16d 3.12d 3.34de 4.25f 3.82ef 0.006 Appearancelike/dislikea 3.01d 3.11de 3.19de 3.32de 3.75e 2.82d 0.02 Color like/dislikea 3.07d 3.17d 3.23de 3.28de 3.87e 2.82d 0.04 Color intensityb 3.16d 3.36de 3.15d 3.25a 3.87e 2.91d 0.02 Amount of fat like/dislikea 3.06d 3.19de 3.26e 3.36e 3.75e 3.09de 0.02 Overall visual like/dislikea 3.00d 3.13d 3.23d 3.34d 3.50d 2.82d 0.009 a Consumerattributeswereevaluatedusinga 5-point scalewhere1= dislike extremelyand5= like extremely. b Consumer attributeswereevaluatedusinga 5-point scalewhere1= light and5= dark. c National Pork ProducersCouncil new freshmeatmarbling scoreswhere11% lipid, 2= 2% lipid; 3= 3% lipid, 4= 4% lipid, 5= 5% lipid and 66% lipid. def Leastsquaresmeanswithin a row lacking a commonsuperscriptdiffer (P fibers are elastic and have the ability to contract and relax. Through the conversion of muscle to meat, muscle proceeds through rigor mortis where muscle fibers losetheir ability to relax andthat results in lossof muchof their elasticity. Biochemical andphysical conditionspresentwhena muscle proceeds through rigor mortis affect the final contractile stateor sarcomere length and tendernessof themuscle. Onephysiological phenomenonthat canoccurduring rigor mortis is called cold-inducedtoughening or cold-shortening. It occurs during the onset of rigor mortis when the muscle is chilled rapidly, the sarcoplasmic reticulum loses its abil ity to bind calcium, so calcium concentrationsin the cytosolof the cell increases.The endresult is that energy stores in the form of ATP are still available when calcium concentration increases and the contractile apparatusof the muscle still has the ability to contract.Themusclefibersthencontractmorerigorously thannormal andupon the inability to relax, the contractile stateof the muscleis shorterthannormal. The result is tougher meat. Sarcomere length is a measure of cold-induced tougheningandit is thedistance between the two Z lineswithin a sarcomere.A sarcomereis thesmallestcontractile apparatusof a muscle fiber andtheZ lines are rigid structuresthat composethe exterior of a sarcomere.Z linesare very strongstructures thathaveto withstandtheforcesappliedduringcontraction.In cold-shortenedmeat, Z line densityincreaseswithin agivenquantity of meat.As long astheZ line hasnot beendisruptedby eitherdegradationor fragmentation from contractile proteinsin super-contracted meat,increased density of Z lines hasbeenrelatedto increasedmeat toughness(Locker, 1960; Marsh and Leet, 1966;Marshet al., 1968).Additionally, musclefibersthatareshorterhavebeen shown not to degradeasrapidly post-mortemasthereis not sufficient room for degradativeenzymesto work. Strength of the structural components within the musclefiber alsohasbeen related to meattenderness.The basic premiseis that asthe structural apparatus of the muscle is degraded and weakened, meat tenderness improves (Koohmaraie, 1988, 1992; Koohmaraieet al., 1988). The structural apparatus of muscle fibersis composedof Z linesandmultiplestructural proteinsthathold the myofilaments of musclefiber in an organized, structural array. Also, the major contractile proteins,myosin andactin, arepart of the structural array in that theyarethepredominantproteinsin themuscle fiber. Degradativeenzymes work to breakapartthe muscle fiber structural apparatus.In living tissue,these enzymesareresponsiblefor proteindegradationandrepair of protein structure. In meat, these enzymes degrade large structural proteins such as titan and nebulin and loosen the strength of the muscle fiber component. The major enzyme system shown to affect post-mortem musclefiber degradation is the calpain proteolytic system (Koohmaraie,1988,1992,Koohmaraieet al., 1988; Goll et al., 1995). This system is composedof -calpain, m-calpain and calpastatin.Calpastatinregulatesthe activities of the calpains that have been shown to degrade structural proteins postmortem (Koohmaraie, 1988, 1992, Koohmaraie et al., 1988). Increasedmyofibrillar degradation post-mortemhas beenrelated to improvementsin muscle fiber tenderness. Goll et al. (1995) 34 Meat processing proposed the theory that actomyosin interactions also may play a role in improved meat tendernesspost-mortem, even though actomyosin does not degradepost-mortem. Goll et al. (1995)proposed that weakening or a decrease in the strengthof the actomyosin interaction post-mortem may contribute to improved tenderness. The ability of myofibrillar proteins to bind waterwithin the muscle fiber is alsorelatedto meattendernessandjuiciness.Myofibrillar proteinshavecharged sidegroupsthatcontain ionic chargesandtheseionic chargesbind water.Actin andmyosin, themostabundant proteinsin themuscle fiber,bind themajority of waterwithin the muscle fiber. The chargeon proteinscanbe eitherpositive or negative andchanges in chargecanbealteredby pH. As pH increases,thereis a net increaseof negative charges and as pH decreases, protein sidegroups becomemore positively charged.As the net charge of proteinsbecomeeither morepositively or negatively charged,ionic forcesincrease andwateris bound or held more tightly to the proteins. Changein net charge of proteins is accomplishedby changingmeatpH. An increase or decreasein meat pH will changetheratio of positive andnegative chargeson protein side-chains andwill alter the ability of muscle proteins to bind water. The isoelectric point of a protein is thepH wherethereis abalanceof positiveandnegative chargeson the protein side-groups.The isoelectric point is wheremuscleproteinshavetheleast ability to bind waterandit is where water-holding capacity is lowest. As meat pH reaches the isoelectric point, meat losesmore water as drip loss during storageanduponcookingor a lower cookyield. Theresultant meatis drier and tougher. Therefore, meatpH is an importantcomponentof meat quality as it relates to the ability of muscle proteins to bind water and the subsequent juicinessandtendernessof the meat. 3.2.3 Meat color Meat color, the major visual factor affecting meatquality, is imbedded within the muscle fiber componentas meat color is a result of pigment-containing proteins that caneitherabsorbor reflect light. In meat, myoglobin is the major pigment-containing compound.The level of myoglobin, the oxidative stateof the heme-ringwithin myoglobin and what is bound to the myoglobin ligand affects meat color. The level of myoglobin within a muscleis influencedby species, muscle function within the animal,andageof the animal.The stateof iron within thephorforin ring of myoglobin(Fe+2 or ferrous; Fe+3 or ferric) and whatcompoundis boundto themyoglobin ligand is mainly affectedby storage conditions of the meat. Meat color from different speciesof animalsand the corresponding muscle myoglobin contentarepresentedin Table 3.4. As myoglobin content increases, color intensity of the meatincreasesfrom white or pink to very dark red. The highermyoglobin contentin beefdifferentiatesit from the lighter color of pork or poultry meat thathasa lower myoglobincontent. However, muscleswithin a speciesanda carcasscanalsovary in color. Musclesvary in myoglobincontent Factors affecting the quality of raw meat 35 basedon thephysiological role of themuscle. High usemuscles,suchasthe leg muscle in chickenandotherspecies, havehighermyoglobincontentdueto the need for myoglobin to store and deliver oxygen in the muscle. Myoglobin contentalsoincreasesasanimals increasein agesothatmeatfrom olderanimals is darker thanmeat from youngeranimals.For example, veal is brownish pink versus beef from three-year-oldsteersthat is bright, cherry red. The increased redness in color within beef is due to higher myoglobin content(Table 3.4). Table 3.4 The relationshipbetweenspeciesof origination of musclefoods,raw meat color, musclefoodsmyoglobincontent,andmajor factorsinfluencingquality of meat Major factors influencingquality Speciesof listed in decreasing origin of Animal Myoglobin Visual orderof importance musclefood age content,mg/g color within a species Beef 12 days 0.70 Brownishpink Tenderness 3 years 4.60 Bright, cherry Juicinessandflavor > 10 years 16 to 20 red to dark red Lamb Young 2.50 Light red to Flavor red Juicinessand tenderness Poultry dark 8 weeks 0.40 Dull red Flavor meat 26 weeks(females) 1.12 Juiciness 26 weeks(males) 1.50 Tenderness Fish dark 5.3 to Dull red to Flavor meatspecies 24.4 dark red Juiciness Texture Turkey dark 14 weeks(female) 0.37 Dull red Flavor meat 14 weeks(male) 0.37 Juiciness 24 weeks(female) 1.00 Tenderness 24 weeks(male) 1.50 Pork 5 months 0.30 Grayishpink Juiciness Flavor Tenderness Poultry white 8 weeks 0.01 Grayishwhite Flavor meat 26 weeks(females) 0.08 Juiciness 26 weeks(males) 0.10 Tenderness Turkey white 14 weeks(female) 0.12 Dull red Flavor meat 14 weeks(male) 0.12 Juiciness 24 weeks(female) 0.25 Tenderness 24 weeks(male) 0.37 Fish white 0.3 to Grayishwhite Flavor meatspecies 1.0 Juiciness Texture Adaptedfrom Miller (1994). 36 Meat processing Therefore, musclecolor hasbeenusedasan indication of maturity andquality within meatspecies. While myoglobin is themajor pigmentin meat,accounting for 50 to 80%of the total pigment, hemoglobin, the major color pigment in blood, can also contributeto meat color. Conditionsduringslaughterthatinfluenceproperblood removalcaninfluencehemoglobin content.A higherhemoglobincontentresults in darker lean. Other meatpigments,cytochromes,catalase,and flavins, exist within muscleandinfluencemeat color, but only to a very minor extent. 3.2.4 Connective tissuecomponent Perimysium, connective tissuesurrounding musclebundles,and endomysium, connective tissue surrounding muscle fibers, provide structural support to muscles. High-use muscles used for work or major movementshave higher connective tissue content than low-use muscles or muscles that provide structural support. Muscles with higher amounts of connective tissue are tougher. This phenomenon is why muscles from thehindquarterof animalsthat are usedfor locomotion, suchas the Bicepsfemorus, Semimembranosus, and Semitendinosus, are inherently tougher than support muscles, such as the Longissimuslumboriumin theloin region.Anotheraspectof connective tissueis the type of crosslinking within the connective tissue matrix. There are two classificationsof bondswithin connective tissue, heat-soluble bondsand heat- insoluble bonds.Collagenis themain fiber in theperimysiumandendomysium connective tissuematrix. During heatingor cooking, a proportion of the bonds canbesolubilized or broken. As animalsage,thepercentageof insolublebonds increases. Increased toughness due to increases in animal age is mainly attributedto theincrease in heatinsolublecollagenbonds.Therefore,connective tissuecontributesto meatquality mainly by its influenceon meattenderness.In young animals,connective tissueaffects meat tenderness mainly through the total amount of connective tissuebetween muscleswithin the sameanimal.As animals increasein age, meat becomestougher mainly by increasing the percentageof heat-insolublecollagen cross-links. In summary, the threemajor components of meat, fat, lean and connective tissue, contribute to meat quality with each uniquely contributing to meat juiciness, tenderness and flavor. While each of thesecomponents has been discussed separately, they are not independent components, but they are interconnected and

interact biologically within the muscle or meat system. Therefore, ante-mortemand post-mortemfactors that affect meat quality may affect any of the threecomponentsandsubsequentlyaffect meatquality. 3.3 Breed and geneticeffectson meat quality As meat quality is affected by the lipid, muscle fiber and connectivetissue componentswithin ananimal,it is not surprisingthatanimalgenetics canplay a Factors affecting the quality of raw meat 37 major role in meat quality. It haslong beenunderstood that the unique genetic code for each animal regulatesthe production of proteins and that genetic variation existswithin meatanimalspeciesfor importantmeatquality attributes. Meat quality traits are generally recognized as being moderate to highly heritable. 3.3.1 Beef In beefcattle,variation in quality in the US hasbeenwell documented through the National Beef Quality Audits in 1991, 1995, and 2000 (Lorenzenet al., 1993; Boleman et al., 1998; McKenna et al., 2002) and the National Beef TendernessSurveys (Morgan et al., 1991; Brooks et al., 2002). Extensive research on factors that contributeto this variation has beenconducted. One source of variation implicated as contributing to this variation hasbeenbreed type. Biological type within Bos taurus cattle, British (Hereford, Angus and Shorthorn)andExotic or Continental (Charolais,Chianina,Gelbvieh,Limousin, Maine Anjou, Pinzgauer, Simmental, and Tarentais,for example) and dairy breeds (Holstein, Jersey and Brown Swiss) has been shown to influence tenderness,but mainly throughdifferences in growth rate,weightat the time of slaughterandfatnessat slaughter.Continental-influenced cattletendto betaller, haveheavier carcassesat a constant fatness, andrequirea longertime on high- energy diets to reacha constantfat endpoint when comparedto British-based cattle. As biological typeinfluencesgrowth rate,fatness, weight, andbodymass, these factorshaveadirector indirect influenceon meattenderness,especially as carcassfatnessandweight can influencecold-inducedtoughnessandmarbling levels. As long as cattle are managedsimilarly and slaughtered at the same fatnessendpoint, differencesin meatquality areminimal. However,dairy-based breeds tend to havehigher marbling levels at a constantsubcutaneous fatness level as selectionfor milking ability appearsto haveresultedin selectionfor higher marbling. Researchers at the United States Department of Agriculture (USDA), Agricultural Research Service (ARS), Roman L. Hruska US Meat Animal Research Center in Clay Center, NE, have examined genetic differences between many breedtypes. The Germ Plasm Evaluation (GPE) programhas completedmultiple cycles.In Cycles I, II andIII, F1 crossesout of Hereford and Angus damsandsiredby Angus, Brahman,Brown Swiss,Charolais, Chianina, Gelbvieh, Hereford, Jersey,Limousin, Maine Anjou, Pinzgauer, Red Poll, Sahiwal, Simmental, South Devon and Tarentais bulls were evaluated for multiple carcassandbeefquality characteristics (Koch et al., 1982a;Kochet al., 1976; Koch et al., 1982b; Koch et al., 1979). While differencesin marbling score andWarner-Bratzler tendernessexisted between Continental-andBritishbasedcattle,differenceswereslight (Table 3.5)aslong ascattlehadbeenfed to a similar fat thicknessor days-on-feed endpoint. If cattle are fed to contain varying levels of fatnessor they are at different physiological points in their 38 Meat processing growth curve, breeddifferences may exist. Thesebreeddifferencesare then a factorof not comparingcattle at thesame endpoint andtheymaydiffer in body mass,fatnesslevel andmarbling level. Diff erencesin tendernessthenaremost likely dueto theeffectsof marbling on meatpalatability, cold-shorteningeffects andconnective tissuedifferences. The main breed effect for meat tenderness has beenbetweenBos indicus versus Bos Taurus cattle. It has been well documented that Bos indicusinfluencedcattlehavehigher shearforcevaluesandgreatervariation. Research hasdocumentedthat as the percentageof Bos indicusbreedingincreases,beef tendernesstendsto decreaseandthe variability in tendernessincreases(Damon et al., 1960; Ramseyet al., 1963; Koch et al., 1982b; Crouseet al., 1989; Wheeler et al., 1990;Whipple et al., 1990;Shackelford et al., 1991)(Table3.6 as adaptedfrom Shackelford (1992)). Early research hypothesizedthat Bos indicuscattleweretougher dueto lower levels of intramuscular fat andhigher connective tissuecontent when comparedto Bos taurus cattle. Wheeler et al. (1990)showedthat Bosindicuscattlehadlower levelsof -calpain andhigher levels of calpastatin.They concluded that calpain activity, as modulated by calpastatin, seemedto play a major role in the inherenttendernessdifferences between Hereford andAmerican Gray Brahmansteers. Table 3.5 Summary of marbling and Warner-Bratzler shear force (kg) (WBS) differencesbetweenbeef cattle breed-typesevaluatedin the Germ PlasmEvaluation programat theUSDA, ARS RomanL. HruskaUS MeatAnimal ResearchCenterin Clay Center,NE Cycle I Cycle II Cycle III Breedgroup Marbling WBS Marbling WBSa Marbling WBSa Hereford 10.0 3.1 10.6 3.2 Angus 13.2 3.2 14.2 3.0 Hereford Angus 11.4 3.4 10.8 3.4 11.4 3.4 Angus Hereford 12.1 3.1 11.9 3.1 11.9 3.2 Jersey 13.7 3.0 SouthDevon 11.7 3.0 Limousin 9.2 3.4 Simmental 10.3 3.4 Charolais 10.9 3.2 RedPoll 11.3 3.3 Brown Swiss 11.7 3.4 Gelbvieh 9.6 3.4 Maine Anjou 11.1 3.1 Chianina 9.2 3.4 Brahman 9.2 3.9 Sahiwal 9.6 4.2 Pinzgauer 10.8 3.3 Tarentaise 10.0 3.7

Adaptedfrom

GPEP,1974;GPEP,1975;GPEP,1978. Factors affecting the quality of raw meat 39 As with otherbreedtypes,variationin beef quality within theBosindicusbreed exists. To understandthe effect of major sire lines within Bos indicus breeds on beef quality in theUS,a five-yearresearchstudy was conductedin the1990s.This researchevaluated steers(nˆ 252)from 15 BrahmansiresandoneNelore sireand born from Hereford (nˆ 44) or Angus (nˆ 208) cows under standard environmentalconditionsto understandif differencein tendernessexisted(Hager, 2000). Sixty pure-bred Angus steerswere included in the last three years.The overall goal of this researchwas to identify Bos indicus sires that produced progeny that hadpositive carcasstraits and that were tenderand lessvariablein tenderness.Quality gradecharacteristicswereobtainedandWarner–Bratzlershear force values(kg) weredeterminedafter 1, 7, 14, 21, 28, and35 daysof ageing at 4ºC. Sire influenced(P< 0.05) leanmaturity, overall maturity, marbling, quality gradeandshearforcevalues(Tables3.7and3.8)andsireaffected(P< 0.05)shear force valuesafter ageing for 1, 7, and 21 days (Table 3.8). The F1 Bos indicus- influencedsteers were less tenderat 1 day and 7 dayspost-mortem than Angus steers(Fig. 3.2).Angussteersreachedtheir maximumtendernessafter7 dayspost- mortem. However,F1 steersshoweda fasterrateof ageingandwerenot different in tendernessafter 14 dayspost-mortemageing thanmeatfrom Angussteers.The rateof ageingwas fasterfor F1 steersthantheAngussteers,andshearforcevalues did not differ between the two breeds after21 daysageing.It canbehypothesized thatsufficient post-mortem ageingcanremovevariation in tendernessbetweenBos Table 3.6 WarnerBratzlershearforce (kg) meansfrom the Longissimusmuscleof cattlediffering in BosindicusversusBostaurus inheritance PercentageBosindicusbreeding Reference Breeda 0 25 38 50 62 75 100 Damonet al., 1960 B 6.22 6.72 6.68 7.14 – 7.79 9.27 Carpenteret al., 1961 B – 3.93 – 5.02 – 4.65 5.29 Ramseyet al., 1963 B 2.31 – 3.03 2.46 – – 3.23 Luckett et al., 1975 B 3.94 4.37 – – – – 6.29 Koch et al., 1982b B 3.44 – – 3.92 – – – Koch et al., 1982b S 3.44 – – 4.27 – – – McKeith et al., 1985 B 4.79 – – 5.77 – – 7.18 Bidner et al., 1986 B 3.90 4.30 – – – – – Riley et al., 1986 B 4.30 – – 6.00 – – – Crouseet al., 1987 B 4.00 – – 7.50 – – – Crouseet al., 1987 S 4.00 – – 8.00 – – – Crouseet al., 1989 B 4.40 5.16 – 5.80 – 6.68 – Crouseet al., 1989 S 4.40 5.64 – 6.64 – 8.41 – Cundiff et al., 1990 N 5.50 – – 7.00 – – – Wheeleret al., 1990 B 4.75 – – 4.75 – – 6.40 Whipple et al., 1990 S 4.70 – 6.40 – 7.70 – – Shackelfordet al., B 4.50 – – – 5.40 – – 1991 a B = Brahman,S= SahiwalandN = Nelore. Adaptedfrom Shackelford(1992). 40 Meat processing Table 3.7 Leastsquaresmeansandstandarderrorsfor quality gradecarcasstraits of F1 Bosindicus Angusor Herefordsteersasinfluencedby sire from Hager(2000). Lean Skeletal Overall Quality Sire maturitya maturitya maturitya Marblingb gradec 1 (nˆ21) 167.73.54d,e 149.52.07 157.31.92d,e 433.612.29h 697.08.32l 2 (nˆ14) 177.34.15e,f 157.62.42 166.12.25h 320.714.40d,e 622.59.75d,e,f 3 (nˆ18) 171.43.76d,e 154.82.19 161.92.03d,e,f,g,h 341.313.03d,e,f,g 637.48.82e,f,g,h 4 (nˆ16) 172.83.87e 154.22.25 162.22.09e,f,g,h 365.213.41f,g 660.29.08h,i,j 5 (nˆ16) 178.64.35e,f 146.02.54 158.92.36d,e,f,g 310.815.11d 611.110.23d 6 (nˆ13) 180.54.33e,f 154.12.52 165.32.34g,h 362.815.01f,g 652.110.16g,h,i,j 7 (nˆ17) 172.03.87e 153.42.26 161.42.10d,e,f,g,h 348.813.45e,f,g 646.69.10f,g,h,i 8 (nˆ17) 170.43.63d,e 153.82.11 161.01.96d,e,f,g,h 367.312.60f,g 660.98.52h,i,j 9 (nˆ17) 173.33.75e,f 152.62.18 161.12.03d,e,f,g,h 343.113.00d,e,f,g 638.28.80e,f,g,h 10 (nˆ15) 168.33.98d,e 147.62.32 156.32.15d 348.213.80e,f,g 648.49.34g,h,i,j 11 (nˆ16) 171.73.97d,e 151.92.31 161.42.15d,e,f,g,h 376.113.76g 671.79.31j 12 (nˆ15) 164.04.07d,e 152.42.37 157.32.20d,e 372.714.11g 665.29.55i,j 13 (nˆ14) 168.64.23d,e 150.02.47 157.92.29d,e 332.214.68d,e,f,g 632.09.94d,e,f,g 14 (nˆ16) 183.83.89f 151.02.27 165.12.11e,f,g,h 339.513.50d,e,f,g 639.19.14e,f,g,h,i 15 (nˆ13) 159.84.36d 154.32.55 156.62.36d,e 451.215.14h 704.110.25l 16 (nˆ14) 170.44.71e,f 149.72.75 158.62.55d,e 303.316.34d 618.111.06d,e P-value 0.003 0.05 0.01 0.0001 0.0001 RSDk 14.6 8.5 7.9 50.5 34.2 a 100= A00 and500= E00. b 100= Practically devoid00 and900= Abundant00. c 100= Canner00 and800= Prime00. d,e,f,g,h,i,j Meanswith different superscripts within a column aredifferent (P Table 3.8 Leastsquaresmeansandstandarderrorsfor Warner-Bratzlershearforce values(kg) of F1 Bosindicus Angusor Herefordsteersas influencedby sire for post-mortemageingperiodof 1, 7, 14, 21, 28, and35 daysfrom Hager(2000) Lengthof storage,day Sire 1 7 14 21 28 35 1 (nˆ21) 4.30.23c 3.45.20b,c,d 3.03.17 2.87.18a,b,c 3.10.17 2.79.18 2 (nˆ14) 4.41.23c 3.57.23b,c,d 3.17.20 2.90.21a,b,c 3.21.20 3.39.21 3 (nˆ18) 3.89.24a,b,c 3.87.21d 3.01.18 2.99.19b,c,d 3.06.18 3.21.19 4 (nˆ16) 3.85.25a,b,c 3.20.21a,b,c 2.76.18 2.59.19a,b 2.80.19 2.75.20 5 (nˆ16) 3.32.27a 3.18.24a,b,c 2.85.20 2.54.21a,b 2.87.20 2.59.21 6 (nˆ13) 4.03.29b,c 3.60.25c,d 2.79.21 3.12.23c,d 3.27.22 3.03.23 7 (nˆ17) 4.34.27c 3.68.24c,d 2.91.20 2.89.21a,b,c 3.40.20 3.19.21 8 (nˆ17) 3.59.23a,b 3.00.20a,b 2.76.17 2.77.18a,b,c 3.05.17 2.79.18 9 (nˆ17) 4.21.25c 3.50.22b,c,d 2.88.17 3.43.20d 3.57.19 2.82.20

10 (nˆ15) 3.44.24a,b 3.32.21a,b,c 2.66.18

2.82.19a,b,c 2.98.18 2.69.19 11 (nˆ16) 4.09.25b,c 3.33.22a,b,c 3.27.19 3.02.20b,c,d 2.95.19 2.91.20 12 (nˆ15) 3.56.26a,b 3.00.23a,b 2.59.19 2.42.21a 2.99.20 2.82.21 13 (nˆ14) 3.96.27a,b,c 3.27.23a,b,c 2.66.19 2.61.23a,b,c 2.97.20 2.81.21 14 (nˆ16) 3.56.25a,b 3.16.22a,b,c 2.68.18 2.75.20a,b,c 3.18.19 2.86.20 15 (nˆ13) 3.28.27a 3.00.24a,b 2.57.20 2.66.22a,b,c 2.74.21 2.53.22 16 (nˆ14) 3.44.29a,b 2.70.26a 2.65.22 2.61.23a,b,c 2.98.22 2.81.23 P-value 0.0001 0.03 0.16 0.01 0.09 0.15 RSDe 0.85 0.74 0.85 0.67 0.65 0.68 a,b,c,d Means with different superscripts within a

columnaredifferent (P indicus andBostauruscattle. Also, differencesin tendernessbetweenBosindicus and Bos taurus cattle can be partially attributed to differencesin post-mortem musclefiber ageingeffectsattributed to differencesin calpastainand/or calpain levels.Interestingly, the relationship between marbling andWarner-Bratzler shear force is very low in Bos indicusinfluencedcattle (Hager, 2000).To understand whatchemical factors(Table 3.9)wererelatedto Warner-Bratzlershearforceover 35 days of post-mortemageing, simple correlation coefficients were calculated (Table3.10). Components related to the myofibrillar component,sarcomere length and calpastatin activity, andthe connective tissuecomponent, collagen amount and solubility, were not highly related to Warner-Bratzler shear force values. However, fat wassignificantly, but only slightly, correlatedto Warner-Bratzler shearforceafter 14 daysof ageing.While it would beexpected that calpastatin would havea higherrelationship basedon the previousdiscussion,it shouldbe notedthat calpain levelswerenot measured. While the evidenceis strong that Bos indicus cattle differ in tendernessfrom Bos tauruscattle, thereis not one factor that contributes to this effect. The lean, fat and connective tissue componentsare interrelated.Obviously, differences in rate of ageingoccurred andmarblingdifferences maybecontributingto differences,but thedatado not support singling out onecomponentasthe contributing factor. Extensive researchin the 1990shasbeendirectedat developmentof beef geneticmarkers.Geneticmarkers for marbling developedin Australia, a marker for marbling that was developedout of the Angelton Project at TexasA&M University, and sevenmarkers for tendernessthat were developedout of the Angelton Project, are being examined for commercial production. However, geneticmarkers identify the geneticpropensity of an animal and they do not guarantee thathigh-quality beefwill result. Production andmanagementfactors that can influence beef quality need to be carefully controlled to ensurean animal hasthe opportunity to expressits geneticpotential. When commercial Fig. 3.2 WarnerBratzlershearforcevalues(kg) for top loin steaksfrom AngusandF1 Angusor Hereford Bos indicussteersfrom Hager(2000). Factors affecting the quality of raw meat 43 useof genetic markers is viable,thesemarkerswill assistin removingvariability associatedwith breed differences. 3.3.2 Pork Diff erencesin ultimate muscle pH, lean color, water-holding capacity and marbling are the major pork quality issuesas color and the ability of muscle Table 3.9 Least squaresmeansand standarderrors for chemical componentsof F1 steersasinfluencedby sire including Angussteersadaptedfrom Hager(2000) Sarcomere Calpastatin, Moisture, Fat, Total collagen, Collagen Sire length,m activity/g % % mg/g solubility, % 1 (nˆ 21) 1.73 2.73 72.28b,c 4.93e,f 2.42 7.55b 2 (nˆ 14) 1.69 2.51 73.15c,d, 3.51b,c,d 2.79 7.12b 3 (nˆ 18) 1.68 2.53 72.97c 3.75b,c,d 2.62 6.98b 4 (nˆ 16) 1.73 2.36 73.07c,d 3.88b,c,d 2.57 7.24b 5 (nˆ 16) 1.68 2.61 73.38c,d 3.15b,c 2.28 9.28b,c 6 (nˆ 13) 1.66 2.68 72.44b,c 4.14b,c,d,e 2.57 7.40b 7 (nˆ 17) 1.66 2.16 72.71b,c 4.171c,d,e 2.38 8.34b 8 (nˆ 17) 1.70 2.53 72.91c 3.89b,c,d 2.69 7.37b 9 (nˆ 17) 1.69 3.02 72.53b,c 3.82b,c,d 2.49 7.23b 10 (nˆ 15) 1.68 2.12 72.70b,c 4.00b,c,d,e 2.56 6.97b 11 (nˆ 16) 1.69 1.90 72.26b,c 4.05b,c,d,e 2.52 7.80b 12 (nˆ 15) 1.70 2.44 72.71b,c 4.44d,e,f 2.44 8.02b 13 (nˆ 14) 1.74 3.56 74.27d 2.94b 2.46 8.23b 14 (nˆ 16) 1.69 2.56 72.47b,c 4.04b,c,d,e 2.37 11.32c 15 (nˆ 13) 1.75 2.63 72.62b,c 4.54d,e,f 2.73 7.49b 16 (nˆ 14) 1.67 2.64 73.42c,d, 3.56b,c,d 2.61 8.26b Angus(nˆ60) 1.75 2.43 71.61b 5.39f 2.65 7.36b P-value 0.27 0.13 0.005 0.0001 0.95 0.03 RSDa 0.11 0.74 1.8 1.5 0.75 3.2 a RSD= residualstandarddeviation. b,c,d,e,f Meanswith different superscriptswithin a columnaredifferent (P proteins to bind wateraffect pork quality. Pork is inherently more tender than beefaspork is much lesssusceptible to coldshortening effectsandpost-mortem ageingoccursatamuch morerapidratethanin beef. Also, pork is slaughtered at physiologically youngeragesso connectivetissueplays a very minor role in meatquality. Pork is alsomoresusceptible to preslaughterstressthat induces morequality defectsrelatedto thecolor andwater-holdingcapacity of the lean. As a largeproportion of pork meatgoesinto further processed products, water- holdingcapacityor theability to hold brinesor non-meat ingredients becomesa muchmoreimportantissue.Marbling, while notasimportantanissueasin beef, haseconomic value in some internationalmarkets andso marbling differences canbe an important trait. Berkshire pigs have darker colored lean, higher marbling scores,higher ultimatepH andmoretendermeat(Table 3.11) (Goodwin, 1994;NPPC,1995; Goodwin, 1997); however, high levels of overall carcassfat and low lean production areissuesrelatedto thepractical productionof theseanimals except for specialty markets.Hampshire hogshavebeenshownto havemoderatepink to grayish-pink color, intermediate levels of marbling,but low ultimatepH and low water-holding capacity (Goodwin, 1997). Most of this effect has been contributedto theNapolegeneeffect (seediscussion below).Durocshavebeen shownto havea higher lipid content andLandracehavea palemeatcolor and low pH (NPPC,1995;Goodwin,1997).Thereforedifferencesin porkquality are related to breed group, however, most commercial pork operations use composite genetic types. Comparison of differences in pork quality between thesegenetictypes is not available and,therefore,direct comparisons cannot be made. However, most major breeding companiesprovide carcassand meat quality datafor comparative purposes.The pork industry hasgeneticmarkers, the Halothane gene and the Napole gene, for pork quality commercially available.Useof these geneticmarkers assistsin removing quality variationand improving overall quality of pork. 3.3.3 Halothane geneeffectson pork quality Thehalothanegenehasbeenassociatedwith thePork StressSyndromein pigs. Fujii et al. (1991)reported a point mutationin theryanodinereceptorregulatory regionof chromosome6 andthis mutationresultedin pigsthatweresusceptible to malignant hypothermia when exposedto halothane gas. The ryanodine receptor is involved in calcium release and regulation from the sarcoplasmic reticuluminto thecytosolof thecell. Whenmutantor homozygote (nn) pigsare exposed to stress,calcium concentrations in the cytosol of the cell increase abnormally and pigs do not have the ability to adequately decreasecalcium concentration in the cytosol or re-establish calcium concentrationsfor muscle relaxation. The result can be either death or near death due to malignant hyperthermia.If theseanimalsarestressedimmediately prior to slaughter,one of two conditions may exist. Either the animals prematurely die or due to increasedmetabolism, pH declinesvery rapidly postmortemandresultsin pale, Factors affecting the quality of raw meat 45 Table 3.11 Ultimate pH asinfluencedby breedtype Breedtype Cinta Belgian Italian Swedish US Poland Reference Berkshire SeneseDuroc Hampshire Landrace Landrace Landrace Landrace Pietrain China Spot Yorkshire Lawrie andGatherum,1962 5.44 5.49 Jensenet al., 1967 5.46 5.33 5.42 5.38 4.57 Hedrick et al., 1968 5.59 5.43 Monin andSellier, 1985 5.40 5.45 5.53 Dazzi et al., 1987 6.03 5.72 5.72 5.92 5.68 5.53 Sellier et al., 1988 5.86 5.78 5.86 Barton-Gade,1990 5.56 5.48 5.46 5.47 Goodwin,1994 5.92 5.72 5.53 5.65 5.72 5.69 5.72 NPPC,1995 5.91 5.85 5.70 5.83 5.84 Lindahl et al., 2001 5.33 5.42 5.44a a SwedishYorkshirepigs soft andexudative (PSE)meat.Selectionof pigswith onecopyof thehalothane gene,or heterozygotes (Nn), hasbeenimplementedby some geneticcompanies dueto therelationship between heterozygotesanddecreased carcassfatnessand increased carcassmeat yields; however, a decreasein pork quality has been associated with heterozygotepigs. Halothaneheterozygotepigshavebeenshown to bepalerin color (Christian andRothschild,1981;Lundstrom et al., 1989;Wilson, 1993; Louis et al., 1994; Goodwin, 1994),havemore drip loss(Lundstrom et al., 1989),havesoftermeat (Louis et al., 1994)with lessmarbling(Louis et al., 1994;Goodwin, 1994),and they weretougher (Goodwin, 1994) thannormal or non-carrier pigs.Therefore, Halothanegenestatus,either Nn or nn, affectspork quality throughincreased susceptibility to shorttermpre-slaughterstressthat resultsin lower thannormal ultimatepH andpaler,softermeatthat hasa higher thannormaldrip andcook loss. Theseeffects result in drier, tougher and less flavorful meat. Goodwin (2002) found that the overall frequencyof Halothaneheterozygote in eight US breedsfrom the National Barrow Show in 1999,2000and2001was6.2%with Berkshire, ChesterWhite,Duroc,Hampshire,Landrace,PolandChina,Spot and Yorkshirehaving4.2,0.6,1.6,0, 1.239,12,and3.3%,respectively, frequencies. He found that Halothaneheterozygotepigs had less 10th rib backfat, larger ribeye areas,lower pH, lighter color, lower intramuscular fat, lower water- holding capacity, higher cook yield loss,and the cookedloin chopsweredrier andtougher. The Halothanegene obviously affects pork quality. While pre-slaughter handling systemsto reducestressdecreasethe impact of this geneon meat quality, the useof homozygote and heterozygote animals for meatproduction negatively affectspork quality. 3.3.4 Napole geneeffect on pork quality TheRendementNapole (RN-) gene,commonly called theNapole gene,in pork is believed to be the causeof red, soft, exudative(RSE) pork (Warneret al., 1997).RSEporkhasa redcolor thatconsumers’ desire,but is softandexudative indicating that the muscleproteins have low water-holding capacity.The RN allele wasfirst suggested to be responsible for the RSEconditionby LeRoy et al. (1990) where the RN genewas identified in two French composite lines including Hampshire lines.TheHampshire hogsexaminedhadlower processing yield andhigherdrip loss in cookedcured products. Warneret al. (1997) later proposed that lower processingyields in RSE pork were due to lower pH and high amountsof glycogenin themuscle andtheysuggestedthatRSEpork wasa result of the presenceof the RN gene.Research hasshown that the RN allele increases muscleglycogencontent by 70% of homozygousand heterozygous RN carriers (Estradeet al., 1993).The RN homozygousandheterozygous RN animals have a modified adenosine monophosphate kinase. Adenosine monophosphate regulates glycogen synthaseand the altered enzyme cannot effectively inhibit glycogenproduction as in normal animals.As glycogen is Factors affecting the quality of raw meat 47 convertedto lactic acidpost-mortem,thehigher levelsof glycogenin meatfrom Napole genecarriersresultsin higher levelsof lactic acid beingproducedpost- mortem.Increasedproduction of lactic acid results in a lower ultimate meatpH (Lundstrom et al., 1996;Enfalt et al., 1997a).A low musclepH resultsin higher drip lossor aslower water-holding capacity(LeRoy et al., 1996) decreasesdue to the meatpH approachingthe meatisoelectric point. Whencomparedto non- carriers, drip lossandcookinglossincreased by 21%and12%,respectively, in meat from carriers (Lundstrom et al., 1996). Studieshaveshownthat the RN genehasother detrimental effects on pork quality besides lower ultimate pH, water-holding

capacity and cook yields. Carriersof theNapolegenealsohavelower protein extractability (Lundstrom et al., 1996).This is dueto the lower protein contentof RN carriers.Estradeet al. (1993)foundthatcarriersof theRN allelehada10%lowerproteincontentof all protein fractions compared to non-carriers. The extraction of salt soluble proteins is essential to the manufacturing of hams and other processed pork products. A decreasein protein extractability resultsin a lower-quality product. The lower proteincontent alsohasan effect on water-holding capacity of meat with the RN gene.The decreasein protein contentof RN carriers leadsto a decreasein the water contentin the myofibrils after curing (Lundstrom et al., 1996). Othernegative effectsof meat from RN carriers includehigher surfaceand internal reflectance and ashvalues(Lundstrom et al., 1996).Also, meat from Hampshire pigs carrying the RN allele has been found to have lower intramuscularmarbling scores than non-carriers or Yorkshires (Miller K.D. et al., 2000).This canaffect the flavor andtendernessof meat. Theeffectof theRN geneon pork palatability hasnot beenconsistent.Some research when comparing non-carriers to RN carriers, found lower Warner- Bratzler shearforcevaluesandhighertraineddescriptive attribute sensory taste intensity andflavor (LeRoyet al., 1996;Lundstromet al., 1996);whereasother studies failed to find thesame taste andtendernessdifferences between carriers andnon-carriers(Lundstrom et al., 1998).Otherpositive attributesfoundin RN carriers havebeenhigher daily gains, fewer dayson test, and carcasses with higher leanmeatcontentanda largerproportion of ham(Enfalt et al., 1997a). Another study from Enfalt et al. (1997b) foundthatcarriershadless sidefatthan noncarriers,largerproportionsof whole hamandwholebackcomparedto non- carriers and Landrace and Yorkshire pigs. Goodwin (2002) showed that the Napole gene did not have an effect on carcasscomposition in eight breeds evaluatedin 1999,2000, and2001,in the US. A genetic marker testis commercially available to testpork for theRN gene. Mill er R.K. et al. (2000) found that the RN allele exists at high frequenciesin the American Hampshire breed in the Unites States and they reported a frequency of 0.630 for the dominant RN allele using the Hardy-Weinberg equilibrium, in the American Hampshire breed.Goodwin (2002) reported the frequencyof the RN genein a representative sample of the US pure-bredpork populationfrom the1999,2000and2001NationalBarrow Showwas5.6%.The 48 Meat processing percentageof pigswithin breed-typehavingonecopyof theRN genewere6.3, 1.3, 0, 66, 0, 16, 25 and 1.3 for Berkshire, Chester White, Duroc, Hampshire, Landrace,PolandChina,SpotandYorkshire,respectively. It is apparentthat the highestfrequency is within theHampshire breed, but otherbreeds,except Duroc andLandrace,hasa small incidenceof theRN gene.Goodwin (2002)foundthat heterozygote Napole pigs did not differ from normal pigs in 10th rib carcass backfat, loineye area, intramuscular fat and cooked loin juiciness.However, heterozygote Napole pigs had lower pH, slightly lighter color and marbling scores,lower water-holding capacityandhighercook loss,but the cookedloin chopsweremore tenderthannormal cookedpork loin chops. The Napole geneaffects meat quality and the incidence of it is at a high enoughfrequency that pork quality is affected by its presence. Selectionto removethis genefrom the pork populationwould improve overall pork quality without significantly affecting leancomposition. 3.4 Dietary influenceson meat quality Dietary influenceson meat quality havebeenextensivelystudied in a numberof meat species.In general, as the energy density of the diet increases,either throughthe useof high-quality grainsthat replaceforagesor by adding fat, the growth rateof the animalsincrease, animals reachslaughterweight at younger ages,theresultant carcassis heavier andhigher in overall fatnessandmarbling, the meat is juicier and speciesspecific-flavors are somewhatdiluted by an increase in fat flavor. When animalsare fed forages,growth rate is slower, animalsareolder at slaughter, the carcasshaslessfat andthe meat is leaner(a positive attribute for diet/healthconsciousconsumers), the meat is darker in color andhasmore speciesspecific lean flavors. Foragefed animals alsomay retain caratenederivedfrom foragesin their fat thatresults in moreyellow fat. Additionally, some foragescontain compoundsthat can be stored in the fat portion of meat that results in meat off-flavors. Therefore, animal diet can negatively or positively affect meatquality. 3.4.1 Feeding high concentrate diets to beef Extensive research hasshown that intensivefeeding of high concentrate diets prior to slaughter positively affectsbeefsensory properties (Meyer et al., 1960; Hawryshet al., 1975;Kropf et al., 1975;Bowling et al., 1977;Schroederet al., 1980;Tatum,1981).This improvementin beefpalatability hasbeenassociated with multiple factors.First, by feedingcattleon high concentratediets,animal overall fatness,muscle mass and carcassweight increase. Therefore, with increased time on high concentratediets,marblingscoresincreaseandsensory panelpalatability ratings increase in beef (Greeneet al., 1989;Williams et al., 1992;May et al., 1992). Whencattlearefed high concentrate diets, they grow more rapidly and they reach slaughter weight in a shorter period of time. Factors affecting the quality of raw meat 49 Secondly, cattle fed high concentratediets are usually slaughteredat younger agesandtherefore,thenegative effectsof increasedageon meatpalatability are diminished.Thirdly, ascattlefed high concentratedietsareheavierat slaughter with carcasses containing higher amounts of subcutaneousfat and greater muscle mass,beef carcassesfrom fed cattle are not as susceptible to cold shortening as these fatter, heavier, more muscular carcasses chill slower. Fourthly, cattle fed high concentrate dietsthat experiencerapid ratesof growth havebeenshownto havehigher amountsof collagen solubility in youngcattle (Aberleet al., 1981;Wu et al., 1981). Therefore,feeding high concentratediets to cattle prior to slaughter hasa positive effect on the structural componentsof the muscle and results in improved meat palatability. Feeding cattle high concentrate diets prior to slaughter also has been associated with removing variation associatedwith nutritional effectsprior to thehigh concentratefeeding period. The lower the energy density of the diet, the more restricted cattle growth is. Cattle enteringthe feedlot that havebeenfed varying energy-based diets from high to low energywould be expected to differ in live weight and composition and therefore their quality also would vary. By feeding high concentratediets,this variation is reduced(Harrisonet al., 1978;Skelleyet al., 1978;Schroederet al., 1980;Miller et al., 1987). Feeding cattlehigh concentratedietsis also relatedto improving beefflavor and juiciness. The meat from animals fed high concentrate diets is brighter, cherry red andthe fat is whiter. It is generally recommended that the effect of forages high in carotene that results in yellow fat can be decreasedor eliminatedby feedinghigh concentratedietsfor up to 90 daysprior to slaughter. Thediet fed to cattleprior to slaughtercanaffect beefflavor. As thediet can affect overall fatnesslevel, the affect of flavor may be due to changesin fat content. Meat with lower fat contentis often describedasbeing morebeefy or brothy, higher in serumy,bloody, livery and grainy/cowy flavors and is more metallic than beefwith higheramounts of fat. Fat most likely either masksthe otherflavor attributesor by slightly coatingthemouth,theability to detectother flavor attributesmay be diminished.Other offflavors canalsobe derivedfrom dietary foragesources. Dietary flavor compoundscan be depositedin adipose cells and result in off-flavors. Melton (1983) summarizedthat the corn in beef high-concentratefinishingdietscanbepartially or totally replacedby cornsilage, a combinationcornsilageandalfalfa, alfalfa hay,or a combinationof alfalfa hay andtimothy andbeefflavor wasnotaffected.Changesin thegrainsourceswithin a high concentratediet mostlikely will not affectbeefflavor. Mi ller et al. (1997) fed beef steerseither a corn, corn/barley or barley based high-concentrate finishing diet 102 to 103 days prior to slaughterto a final live weight of approximately495kg. Cookedtop loin steaksdid notdiffer in cookedbeefflavor intensity or in any beef flavor attributedueto grain source of the diet. The meatfrom beeffed corn-baseddietscandiffer in flavor from pasture-fed beef.Mostof theflavor differenceis dueto fatnessdifferencesin thebeef(Melton, 1983).Whenpastureandgrain-fedcattleareslaughteredatsimilar fatness,Melton (1983) found that beef from pasture-fedcattle was still less desirable.These 50 Meat processing differences were most likely due to deposition of feed-derivedcompounds depositedin the fat. Cattle fed either bromegrassand bluestem;bluegrassand clover;fescue,orchardgrass,andclover;fescuealone;flint hills grass;nativerange grass;foragesorghum;orchardgrassandclover;oats,rye, andryegrass;millet or coastalbermudagrass;andbermudagrasscloverandsudangrasshadlower flavor ratings.Supplementingcattlewith grainduringpasturefeedingwill diluteoutthese effectsor feedingcattlefor 90 to 100dayson grain-baseddietsprior to slaughter will reducethe negativeflavor effectsof thesegrasses. Theeffectsof nutrition on lambquality arevery similar asdiscussedfor beef. As lambsare ruminants,feedinggrain-baseddiets hassimilar effectsas those discussed for beef. However, feedinghigh-concentrate diets to lambsprior to slaughter is not as commona practice as in beef. Lamb can be slaughtered directly afterbeingfed forageor grass-baseddiets.As long aslambsarefed to a fat-constantendpoint, differences in tendernessarenot generally reported. The most significant impact of feeding lamb or beef on forage-baseddiets is the potentialfor off-flavors derivedfrom forage-basedcompounds. Feedingof dietary supplementssuchas vitamins hasbeenshown to affect meatquality. Feeding of vitamin E hasbeenshown to improve color stability and extendshelf-life of beef. Vitamin E is fat-soluble and is deposited in cell membranesandadiposecells.It is a strongantioxidantandmost likely worksto control lipid oxidation and color deterioration throughits antioxidantfunction (FaustmanandWang,2000). 3.4.2 Dietary effects in pork In pork production,the useof high energy grain diets (soy beanand corn) is standard, themaineffectsof diet on porkquality arerelatedto thelysinelevel in thediet or the level and/orquality of the fat (fatty acid composition) in thediet. TheNPPCconducteda studywith six pork genotypesthatwerefed oneof four dietsdiffering in lysinelevel (1.25,1.1,0.95and0.8%lysine).Hogsfed thediet containing the lowest lysine level hadhigher overall carcassfatnessandhigher intramuscular fat content. So diet could affect marbling level, but at the detriment of decreasing carcassleanness. Theincreasedlevel of marbling would mostlikely not offset the increasedproduction andcarcassyield costassociated with decreasingcarcassleanness. Altering the fatty acid composition of the diet in non-ruminantsinfluences the final fatty acidcomposition of theanimal’s fat. In ruminants,themicroflora biohydrogenate unsaturatedfatty acids and it is more difficult to modify beef and lamb fatty acid composition by dietary meansunlessrumen-protectedfats are fed. St. Johnet al. (1987) fed growing pigs a high-oleatediet and found higher muscle and adipose tissue oleate levels. However, meat flavor and palatability were altered. High-oleic cookedLongissimus chopswere juicier, hadhighertendernessscores,andflavor wassimilar to chopsfrom traditionally fed hogs(St. Johnet al., 1987).The

higherunsaturatedfatty acid composition foundin themeatfrom animals fed thehigh-oleic sunflower containing diet was Factors affecting the quality of raw meat 51 softer, oilier andwould beconsidereda visual quality defect.While fat flavor is dependenton thecompositionor fatty acid profile of thefat, slight alterationsin the fatty acid profile may not significantly affect flavor. The sourceof the fat may also affect cooked pork quality. When pigs were fed canola oil, the subsequentmeathad more off-fl avor, lower quality scores,and lower overall palatability ratings thanmeat from pigsfedeitheranormalswineration,animal- fat-, safflower oil-, or sunflower oilbaseddiets.While alteringthe fat source in the diet canaffect the fatty acid profile in the subsequentmeat, the decreasein the fatty acids associated with increasinghuman serum cholesterol levels is minimal andmost likely would not affect the overall healthof consumers. 3.5 Rearing and meat quality The rearing or housingof animalsprior to slaughtercan affect meat quality. Theseeffectsaremainly dueto the lack of stressor the level of stressinflicted on the animal due to the rearing environment. If animals are housed in conditions that result in lower ratesof gain thenanimalsmay be slightly older andmay not havethesamelevel of fatnessastheir counterpartsreared in more desirableconditions.Free-rangeanimalsalsohavethe potential to haveaccess to a highervariety of feedstuffs prior to slaughterthat may affect the flavor of thesubsequentmeat.For example, rangefed hogswould haveaccessto forages during some partsof the year that may result in off-fl avorsin their meat (see previousdiscussion), but thiseffectwouldbeseasonalandbasedonwhattypeof forages were available. In general, confinement feeding has minimal to no effects on meat quality. If animals are over-crowded, there may be limi ted accessto feedandwaterandanimals exhibit undesirable socialbehaviors such as fighting, chewing and inability to rest properly. In thesesituations animal growth will beaffectedandthesubsequentmeatmaybelower in overall fatness andmeat from theseanimals may havea higher incidenceof quality problems related to stressduring slaughter. 3.6 Slaughtering and meat quality The conversion of muscleto meat or the live animal to a carcasscan impact meat quality. Rigor mortis, Latin for ‘stiffening after death’,is the processthat themuscleproceedsthrough in orderto becomemeat.During thisprocess,stress induced on the animal, either long- or short-term,will affect how rapidly the processof rigor mortis will proceed. 3.6.1 Longterm stresson meat quality Animals exposed to long-term pre-slaughter stresshave reduced glycogen suppliesat slaughter.Upononsetof rigor mortis,pH declinedoesnot proceedat 52 Meat processing a normalrate.Thesubstrate glucose,that is derivedfrom glycogen,is converted to lactic acid. The build up of lactic acid is responsible for post-mortem pH declinein muscle.If post-mortempH decline doesnot proceednormallyandthe ultimatepH is higherthannormal(greater than6.0), theresultant meatis darker in color, hasa firm texture, hasa high water-holding capacity andhaslessdrip lossandfreemoistureon themeatsurface. Themeatis definedasdark,firm and dry or DFD. When DFD meat is cooked, it is often described as being juicy, tenderandvery intensein flavor. Somedescribe the flavor asserumy,mustyor old. Additionally, due to the high pH, DFD meat will spoil more rapidly. Conditions that induce long-term stressare long transit times, exposure to extremesin temperature (hot or cold), extendedperiods without food, bulls expressingsexual behavior, or improperhandlingprior to slaughter. It is obvious thatconditionsimposing long-termstressshould beavoidedin orderto improve quality. 3.6.2 Short-term stresseffects on meat quality Short-termstressresultsin pale,soft andexudative meat(PSE).This meathasa lower thannormal pH that resultsin meatthat is palein color anddoesnot have the ability to hold water.During cooking, PSEmeatwill losea high amount of moisture and the resultantmeat will be drier, tougher and not as flavorful. Improper handling, roughhandling, mixing of pensduring transportation or at the slaughter plant, poorly designedholding and handling facilities at the slaughter plant,andother conditionsthat induce stressjust immediatelyprior to slaughter canresult in PSEmeat. Whenanimalsbecomeexcited pre-slaughter, metabolism associated with the flight or fight mechanisms is increased. Body temperature increases and glycolytic metabolism is stimulated. During exsanguination, the blood supply is no longer able to help regulate body temperature and remove the products of anaerobic metabolism. As a result increased body temperaturein combination with rapid metabolism results in a fasterthannormalpH declineandsomeprotein denaturationdueto higherbody temperature. The combined effect of a lower pH and protein denaturation contributeto the lower water-holding capacity of the meat.The higheramount of free-water providesa higher reflective surfacefor light so that the meat is paler in color. The weakerprotein interactions result in softer, lessfirm meat that also providesgreaterreflectancesurfacefor light contributing to the paler color.TheNPPCdefinedvisualstandardsof PSEmeat in thehamandloin chop because final meatpH is a continuous variable that is difficult to categorize. UltimatepH shouldbe consideredan importantquality variableas it accounts for short-term pre-slaughter stresseffects andthe subsequentvisual andeating quality of the meat. The RSE condition discussed previously in 3.3.4 is a result of higher glycogenlevels in meatprior to slaughter.During the conversion of muscleto meat,as thereis a higher amount of substrate for the conversionof glucoseto lactic acid, the resultantmeathasa lower thannormalpH, but not aslow asin Factors affecting the quality of raw meat 53 PSEmeat.TheRSEmeat doesnot havethepalecolor associatedwith PSEmeat and the RSE condition, in general, is not associated with pre-slaughter stress. Eliminationor minimizationof short-termpre-slaughterstressobviously affects pork quality. To improve overallpork quality andconsistency, managementand handling practicesmustnot induce short-term preslaughterstress. 3.6.3 Stunning method effectson meat quality The type of stunning methodusedto immobilize animalsduring the slaughter processcanaffectmeat quality eitherthroughinducing short-term pre-slaughter stressor it can affect blood removalupon exsanguination. The most common methodsof stunning includeanapparatus that inducesa concussion, referredto as concussive methods,the use of electricity to immobilize and concussthe animal, or exposure to CO2 that results in an immobilizedstate.Cattlearemore commonly immobilized using concussive stunning methods and hogs are immobilized generally with electricity, but also CO2 stunningis usedin some countries.Electrical stunningcanbeplacedon theheadonly, on theheadto the back or on the head to the brisket. With electrical stunning an epileptiform seizureis inducedsothat theanimalis insensible to pain. Therearetwo phases of these seizures,tonic andclonic (Gregory, 1985).The induction andstrength of the seizuresis dependenton the amount of current andthe areaof the brain that thecurrentaffects.Hoenderken(1978)defineda minimumrequirementof a currentof 1.25to 1.3A that is maintainedfor threesecondsusing a voltageof at least 240V for electrical stunning. During electrical stunning, kicking canoccur during the clonic phaseasthe brain’s inhibitory influenceon the spinalcord is reduced.This canresult in increased time for shackling, increasedworker risks and lesseffectiveexsanguination. Pigsimmobilized with CO2 aremore relaxed(Channon et al., 2002).Useof head-to-back or head-to-brisket stunning electrodeshas been considered the most humanecompared to headto-head stunning as these methods induce cardiac fibrillation that resultsin cardiac arrestandthese pigsshowlesskicking (Wotton et al., 1992).With cardiac arrest, pigs will not regain consciousness. With head-to-headstunning, there are some incidenceswhere pigs regain consciousness.A disadvantageof head-to-backelectrical stunning is that there can be someincidence of broken vertebraeif too high a voltage is applied. Brokenvertebraearereducedby applyinghead-tobrisketstunning. Carbon dioxide stunning has been shown to reduce the incidence of ecchymosis(Gregory,1985)andasanimalscanremainmotionlessfor up to 60 seconds, kicking is reduced during shackling (Larsen, 1982). Worker safety therefore is reduced with CO2 stunning. However,CO2 stunning in itself does not reducethe incidenceof PSE,but asanimalsstunnedwith CO2 havereduced stress, meatquality is betterthanwith electrical stunning(Barton-Gade,1993). Channon et al. (2002) found that hogs stunned with CO2 had higher pH than head-to-brisket and head-only stunned hogs in the 5th–6th thoracic after 40 minutes,90 minutes,3 hoursand6 hours, but after24 hours,pH did not differ in 54 Meat processing meatfrom animals stunnedby the threemethods. Drip loss (%) washigher in meatfrom animals stunned with head-tobrisketstunning and ecchymosiswas lower in animals stunnedusingCO2. Hemoglobin content of meat is strongly influenced by conditions immediately prior to and during exsanguination at slaughter.Pre-slaughter stress, inadequate severing of the artery or vein used for exsanguination, extendedtime between stunning and exsanguination, and improper suspension of the carcassduring exsanguination canrestrict the volume of blood removed. Whenhemoglobin contentis higher in muscletissuedueto improper bleeding, ecchymosiscanbeincreasedandmeatcanbedarkerredandtastemoremetallic. Properapplication of stunning andproper blood removalduring exsanguination can affect meatquality. Carein properly applying thesemethodsis needed to reducevariation in quality. 3.6.4 Electri cal stimulation effectson meat quality The useof electricalpulsesto useup energyreservesin meatis calledelectrical stimulation.Savellet al. (1978)showedthat by applyingelectricalstimulationto beef carcasses, cold-induced toughening was reduced. They showed that electrically stimulatedbeef carcasseshad acceleratedpost-mortempH decline and longer sarcomeresthat resultedin more tendermeat.High or low voltage electricalstimulationcanbe usedto reducevariation in beefquality. The major differencesbetweenlow-voltage and high-voltageelectrical stimulation is that lowvoltageelectricalstimulationmustbeappliedearlyin thepost-mortemprocess and resultsin more gentlemusclecontractionswhen comparedto high-voltage electricalstimulation.Additionally, with high-voltageelectricalstimulationthere canbe sometearingat the molecularlevel in musclesthat arerigorouslyworked that provides additional tenderness improvements. Electrically stimulated carcassesalsohavebrightercherryredcolorat shorterchilling timespost-mortem. As rigor proceedsat a more rapid rate in electrically stimulatedbeef carcasses, ultimate pH is obtainedmore rapidly and post-mortemphysiological changes stabilize sooner. Some researchhas shown that electrically stimulated beef carcasses have brighter cherry-red color and higher amounts of marbling. Carcasseswith low levelsof externalfat, usually lessthan0.64cm, chill rapidly andtheresultantLongissimusmusclemayappeardarkerredalongtheexteriorrim of themeatandbelighter in color in thecenter.This

conditionis calledheatring, but it is actuallyaresultof pH differencesin themuscledueto amorerapidchilling of theexteriorsurfaceof thecut comparedto thecenter. Theexterior surfacewill havea higher pH that is a result of rapidchilling in leancarcasses.At cold temperatures,glycolysisproceedsat a reducedrateuntil it eventually is halted.In rapidly chilled muscle, glycolysis haltswhen thereis still substrate, glucose, available for further pH decline, but the system to convert glucose to lactic acid is not functioning. Therefore, ultimate pH is higher.In thecenter of themuscle,rigor mortis continues at a morenormalrate andglycolysisis not limited dueto cold temperatures.TheultimatepH is lower. Factors affecting the quality of raw meat 55 Electrical stimulation reducesor eliminatesthis effectby forcing themusclesto work anduseup ATP reserves,rigor mortis proceedsat a more rapid rateand ultimate pH is more closely reachedbefore chilling can inhibit glycolysis and rigor mortis development. Electrical stimulation hasnot commonly beenappliedto pork. As pork has more problemswith rapid ratesof post-mortem pH declinedue to short-term excitement,electrical stimulation traditionally hasinducedhigherlevels of PSE. Researchis continuing on modifying electrical stimulation to address quality problemsin pork. 3.7 Other influenceson meat quality Storage of meat can strongly affect quality positively and negatively. The positive effect of meat storageinfluencesmeat tenderness,also referredto as meat ageing. During refrigerated post-mortem storage, meat tenderness improves.The major factor responsible for post-mortemimprovementin meat tendernessis degradation or proteolysis of muscle proteins. Proteolysis of muscle post-mortem has mainly contributed to sarcoplasmic Ca2+-dependent proteases,the calpains, and the level of their inhibitor, calpastatin. The physiological changes in post-mortem muscle have been associated with degradationof Z-lines, troponin-T,titin, nebulinanddesminandtheappearance of a 95,000daltonand30,000daltoncomponents.During post-mortemstorage, themajorimprovements in tendernessoccurwith thefirst 7 to 14days(Fig. 3.2), but degradation continues with increasedstorage, but at a slower rate. The negative effectof meatstorageonmeat quality is dueto microbial growthand/or lipid oxidation.Both of theseprocessesresult in endingthe shelflife of meat. 3.8 Summary: ensuring consistencyin raw meat quality Meat quality and consistency are important in ensuringconsumersatisfaction. Quality of meat is affectedby the genetic propensity of the animal, how the animal is reared,and the nutritional status during production.Thesefactors affect the fat, lean and connective tissue component of meat and therefore influence meat quality. Genetic differencesare being understood as genetic markers are being developedfor many major quality characteristics within species. As the production segment selects animals to maximize quality, reduction in meatquality canbe obtained. However,theseanimals mustbe fed andrearedto maximizequality. Quality alsois stronglyinfluencedby conditions at theslaughter plant.How animals arehandledpre-slaughter affectsthe rateof rigor mortis. The application of stunning and exsanguination methodsthat ensure reducedanimal stressare importantto meat quality. The applicationof electrical stimulation andhow the carcassis chilled influencethe rateof rigor mortis andsubsequentmeat quality. 56 Meat processing 3.9 Future trends Quality asa meat industry issuewill continue. Providing consumers with high quality, consistent productis a key to the successof the meatindustry aswith any food entity. Today’s consumers demandconsistency and quality and their demandsaremet by othersegmentsof the food industry. Thoselivestock/meat producers who can ensure consistentquality will be the viable playersof the future. To ensure consistency and quality, links between the production segments of the livestockindustry that havegeneticverification of animalsand that then managetheseanimalsto maximize their geneticpropensity will be producersof thefuture.Theseedstockandcommercial production segmentswill either be vertically integratedor therewill be alliancesbetweenproducersto form joint venturesto produce animalsof consistentquality, much like thelarge poultry companies in the United States.The slaughter and manufacturing segments of the meat industry will havecontrol pointswithin their production segments to assuremeatquality andwill control theendproduct from slaughter to the final package for the consumer. Technological advances to improve meat quality will be viewed as interventionsto help control consistencyand quality. A fully integrated meat production system that assuresquality will haveeconomicbenefit andreturns. Products will bebrand-identified andcarry a quality reputation asa component of marketing the product. 3.10 References ABERLE E D, REEVES E S, JUDGE M D, HUNSLEY R E and PERRY T W (1981), ‘Palatability and muscle characteristics of cattle with controlled weight gain. Time on a high energydiet’, J Anim Sci, 52, 757–763. AMSA (1995), ‘Research Guidelines for Cookery, Sensory Evaluation and Instrumental Measurements of Fresh Meat’, American Meat Science Association and National Livestockand Meat Board, Chicago, IL. BARTON-GADE P A (1990) Pork quality in genericimprovementprogrammes– the Danish experience. Proc. of the National Swine Improvement Federation Annual Meeting.DesMoines,IA. BARTON-GADE P A (1993), ‘Effect of stunning on pork quality and welfare: Danishexperience’, Allen D. Leman SwineConference, 20, 173–178. 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4.1 Introduction The most common dietary problems in developed countries are due mainly to over-nutrition. The incidences of overweight, obesity and adult onset-diabetes are increasing steadily. Cancer is now the most common cause of death in many developed countries. The most common cancers are breast, lung, bowel and prostate, which are virtually absent in some developing countries. However, even in our affluent society, we also see signs of nutritional inadequacies. For instance, in the UK nearly a half of females aged between 11 and 14 are not getting enough iron in their diet, while more than a third are not getting enough zinc (Gregoryet al., 2000). We are living in a society where both signs of over- and undernutrition occur side by side. To correct for these nutritional paradoxes we as consumers have to get the balance of nutrients, energy and physical activity right. The objective of this chapter is to highlight the nutritional role that meat can play in modern society. The National Food Survey for 1999 (Ministry of Agriculture Fisheries and Food, 1999), included a special analysis on meat and meat products consumption in the UK. It stated that ‘meat, meat products . . . are important contributors to the intakes of many nutrients in the British diet’. Data from this survey showed that meat and meat products supply: energy 15%, protein 30%, fat 22% (saturated fatty acids (SFA) 22%, monounsaturated fatty acids (MUFA) 27%, polyunsaturated fatty acids (PUFA) 15%), vitamin D 19%, B2 14%, B6 21%, B12 22%, vitamin A equivalents 20%, niacin 37%, zinc 30%, iron 14%. Meat has been a major part of the human diet for at least 2 million years. Human genetic makeup and physical features have been adapted over 4.5 million years for a diet containing meat. An example of this adaptation is our 4 The nutritional quality of meat J. Higgs, Food To Fit, Towcester and B. Mulvihill, Republic of Ireland presentteethand jaw structure, which havedevelopedto becomeefficient at chewing and swallowing meat.Meat is a highly nutritious and versatilefood. Theprimary importance of meat asa food lies in the fact thatwhendigestedits protein is broken down releasing amino acids, these are assimilated and ultimately usedfor therepairandgrowth of cells.Meat is a nutrient densefood, providing valuable amounts of many essentialmicronutrients. Meat supplies fatty acids,vitamins,minerals,energyandwaterandis involvedin thesynthesis of protein, fat andmembranesin the body. Traditionally, meatwas considered a highly nutritious food, highly valued and associated with good health and prosperity. As such, western societies gradually increased consumption with increasing affluence.The healthy image of red meat gradually became eroded during the 1980s, when the lipid hypothesis focusedattention on the fat contributed from meat. The British Government’s Committeeon Medical Aspects of Food andNutrition (COMA) report on coronaryheart disease(CHD) in 1984 identified meat as a major sourceof saturatedfat, contributing a quarterof UK intakes(COMA, 1984). Although the multifactorial natureof CHD risk is now widely acknowledged (British Nutrition Foundation,1996;COMA, 1994), thehealth imageof redmeat remainstarnisheddueto this negativeassociation. More recently,we haveseen thepublication of two reports on diet andcancer (World CancerResearchFund, 1997; COMA, 1998). These reports associated red meat consumption with increased incidence of certaincancers, in particular, colorectalcancer (CRC), despite the existence of conflicting evidence. Both of these reports issued guidelineson the limit s of red meatoneshould consumeto reduce the risk of developing CRC, therebynegatively influencing the imageof red meat. The 1990s also sawmajor publicity on non-nutritional issuesincluding animal health concernssuch as bovine spongiform encephalopathy (BSE) and more recently the returnof foot andmouthdisease(FMD) to Britain. The last 25 years havebeenthemostturbulentregardingissues surrounding meat consumptionwith muchof the publicity beingnegative thusplaying down meat’snutritional value. The negative nutritional image that surroundsred meat is in some way responsible for the decreasein expenditure. In 1999,25.8%of expenditure on homefood in GreatBritain wasspenton meatandmeat products (Ministry of AgricultureFisheriesandFood, 1999).This is a significantdropcomparedwith 32.1%in 1979.During this time period therehavebeenmajor changesin the typeof meat thatpeoplearebuying in theUK. Expendituresonbeef, lamb,pork, baconand ham eachfell, whilst expenditure shares on poultry and on other meatshasrisen.The major growth areain processedmeatsandmeat products hasbeenfrozenconvenience meatproducts, meat-based readymealsandother meatproductssuchasChinese and Italian mealscontainingmeat(Ministry of Agriculture FisheriesandFood,1999).Therearemany factors responsiblefor thesechanges, the tarnishedimage of red meat being one such factor. Other influencing factors include changesin lifestyle trendswhich sawthe drive for conveniencefoods and the resultantresponsiveness of the industry to this has greatly influencedthe changingmeatbuying habitsof consumers. The nutritional quality of meat 65 4.2 Meat and cancer Meat consumption has been implicated in many cancers,as being either protectiveor causative,depending on the typeof cancer.Meatconsumption has beenshown to protectagainstcancersof thestomach (Hirayama,1990;Tuynset al., 1992;Azevedoet al., 1999),liver andthe oesophagus(Zeigler et al., 1981; Tuynset al., 1987,Nakachiet al., 1988).Thesearethreeof thetop five cancers globally. On theother handmeatconsumption hasbeenimplicatedasa causeof colorectal(colon andrectal),breast andprostatecancer, with themainemphasis being on (CRC). CRC is the fourth most common cancerin the world, but in Europe and other Westerncountries it is second in terms of incidence and mortality (after lung cancer in menandbreastcancer in women)with 190,000 new casesper year in Europe(Black et al., 1997; Bingham, 1996). There is strong evidence from epidemiological studies showing that diet plays an important role in most large bowel cancers,implying that it is a potentially preventable disease(Higginson, 1966; COMA, 1998) The precise dietary componentsthat influenceCRC risk havenot beenfully elucidated. However, epidemiological studies suggest that high intakes of fat, meat and alcohol increase risk, whereas vegetables,cereals andnonstarchpolysaccharides, found in fruit andmany other foods, decreasethe risk (Bingham, 1996).For manyof these dietaryfactorstheevidenceis equivocal.In thecaseof meat,theevidence is conflicting, early cross-sectional comparisons attributed much of the worldwide variation in CRC incidence to fat and animal protein consumption (Armstrongand Doll, 1975). In contrast, subsequent case-control and cohort studies aremuch lessconsistent(Hill, 1999a). Meat consumption andCRC becamea high-profile issueduring 1997–1998 with theglobal launch of theWorld CancerResearchFund(1997)report,timed to coincide with the publication of the British COMA report, both on diet and cancer. The WCRF report was particularly negativetowards red meat,which fuelled the launch publicity. This stimulated severalcritical appraisals of the report, all challenging the conclusionsregarding meat (Hil l, 1999b). The scientific evidenceis not sufficiently robust to recommenda maximumof 80g/ day red meat as pronounced by the WCRF and the initial announcementby COMA for a similar recommendation was subsequently revised.Most of the datashowinganassociation between meatconsumption andCRCareAmerican, whereasseveralstudiesconductedoutsidetheUS (manyin Europe)haveshown no such relationship (Hill, 1999a). On final publication, COMA (1998) reassuredUK consumers that averageconsumption levels (90g/dayof cooked redmeat)wereacceptable.COMA suggeststhathigh consumers, lessthan15% of the UK population, eating above140g/daymight benefit from a reduction. Equally important, this report acknowledged that meat and meat products remain a valuable sourceof a number of nutrientsincluding iron and that for many amoderateintakemakesanimportantcontributionto micronutrientstatus. The potential effect on iron statusof further reductionsto redmeat intakeswas subsequently investigated,asrecommendedwithin theCOMA report.Giventhat 66 Meat processing a 50% reduction in intake would result in a third of women having low iron intakes (below 8 mg/d), the appropriateness of public health messages concerning meatconsumption shouldbe carefully considered prior to reaching the media(GibsonandAshwell, 2001). Various componentsof meat (protein, iron, and heterocyclic amines)have beensuspected of contributingto the development of CRC. Dietary protein is broken down in the body to amino acids, which are further degradedto ammonia, which may havecancer-initiating effects.The human colon is also rich in amidesandaminesthat aresubstratesfor bacterialnitrosation by nitric oxide(NO) to N-nitrosocompoundsthatarefoundin humanfaeces.Thereis no conclusive evidencethatproteinderivedcompoundscanincrease cancerrisk in humans.It is hypothesised,but not yet established, that the intakeof iron from meatandother iron-rich foodsmayincrease therisk of cancervia theproduction of free radicalsin the body. Heterocyclic aminesare formed by the Maillard reactionsthat involve amino acids,sugarsand creatine,during cooking. They areusually producedduringcooking at very high temperatureson thesurfaceof meat,suchasfrying, grilling or barbecuing but they areminimal when meatis steamed, microwaved or marinated. The heterocyclic amines are known mutagens in vitro andcarcinogensin rodents. The most abundant heterocyclic aminesproducedin meatis phenylimadazopyridine (PhIP), which is a relatively weakcarcinogencomparedto otherheterocyclic aminessuchasIQ andMeIQ. The role of heterocyclic amines in causingCRC is not fully elucidated in humans. Truswell summarisedthe evidencein Hill (2000)andshowed that 20 out of 30 case-control studies and 10 out of 14 prospective studies showed no relationship between meat intake and CRC with some of the results of the remaining studiesbeingconfusedandoneprospectivestudy showinganinverse correlation between meat consumption and CRC risk (Hill, 2000). If meat consumption wereassociatedwith increasedrisk for cancer, onewould expect mortality from cancerto be much lower amongvegetarians. In a recentmeta- analysis of five cohortstudies, results haveshown no significant differences in mortality from cancerin general, and more specifically mortality in stomach, breast,lung, prostateandcolorectal cancer between vegetariansandomnivores (Key et al., 1998, 1999). If red meat consumption were associated with increasedrisk for CRC,onewould expect a decreasein theincidenceof CRCto occurover time asa resultof decreasingmeatconsumption trends.During the past30 years, redmeatconsumption in theUK hasdecreasedby approximately 25%,while during the sametime the incidenceof CRC hasincreasedby about 50% (Hill, 1999b). Similarly, if meat consumption were associatedwith increased risk for CRC, one would expect the ratesof CRC to be higher in countries with high meat consumption and lower in countries with low meat consumption. The Mediterraneancountrieseatmore red meatthanfor instance theUK yet these countrieshavelower CRCrates(Hill, 2000).Suchparadoxical evidenceis further evidencethat, at

current levels,meatconsumption is not a risk factor for CRC incidence. The nutritional quality of meat 67 Epidemiological associations between dietary components,specific foodsor foodgroupsandchronic disease,suchascancer,canidentify risk factors,butare generally not sufficient to establishcauseandeffectrelationships. Findingsfrom epidemiological studiesmust be combined with other typesof evidence(e.g. animal experiments, human clinical trials) before a persuasive causal relationship can be established.CRC is multi-factorial; it is confounded by diet, smoking, alcohol, physical activity, obesity, aspirin use,age and family history. Thereareknown protectiveandcausativefactors.It is well known that daily consumption of vegetables and meat reducesthe risk of cancerat many sites,whereasdaily meatconsumption with lessfrequentvegetableconsumption increases risk (Hirayama,1986; Kohlmeier et al., 1995; Cox and Whichelow, 1997).Evidencesuggests that it is the reducedintakesof the protective factors suchasvegetablesandcereals that arethe main determinantsof CRCrisk with meat beingcoincidentally related. There is a need to assess the role of meat when consumed in normal quantities, by normal cooking methods, and within the context of a mixed, balanced,diet. The methodof cooking meatand the degreeof browning is of particular importance to this whole issue.A major effort by International Meat Industry partners hasattempted to raiseawarenessof the complexitiesof meat preparationandcooking habitsandhow these differ between countries.Dietary assessmenttechniquesadoptedby nutrition scientistscurrently do not takefull account of the diversedifferencesbetweenmeatproducts world wide and the consequent influencesthese may have on the body. For example, it is well recognized that meat is often cookedmore evenly through the musclewithin Europe,whereasit tendsto be ‘blackened’ on theoutside whilst remaining rare on the insidein North America.This maybeonereasonfor thegreater negative findingsin Americanstudiesof therole of meatin CRC,compared to European studies. This hitherto unexplored facet of meat consumption may have far- reaching implications for interpretation of epidemiological dataandultimately for public health recommendations. Certainmarinadesapplied to meatbefore cookingwill reducethequantity of potential carcinogenicmaterials present. The application of knowledge in this area to the production of processed meat products with all the nutritional benefits and none of the potentially harmful componentswould be progressive indeed. In summary, it is important not only to examine the relationship between meat consumption and CRC alone, but also meat preparation and cooking differencesin conjunction with protective factors, such as vegetables and cereals.At ameatanddiet workshop, it wasstated:‘It is time thatthemeat CRC story was laid to rest, so that we can get back to recommendingthat young womenof childbearing ageeatmeat asa ready source of available iron’ (Hil l, 2000). Nevertheless, it is sensibleto considerthat there must be an optimal rangefor meat intakesin order to ensure a balanceddiet is achieved, whilst optimal weight is maintained.From this practicalperspectiveCOMA’s (1998) suggested intakerangeof 90–140gcookedmeat perday, is sensibleasa public health message.The overemphasison reducing meat however, rather than 68 Meat processing encouraging greater accompanyingplant food intakehasservedonly to confuse the public (Hill, 1999b). Evidence suggests that the risk of cancer will be reducedto a greater extentby increasingintakesof fruit andvegetablesthanby lowering meat intakes. Once again, the move towards pre-preparedmeal solutions providesan opportunity for manufacturersto developrecipeswith a healthy balanceof meat and vegetable ingredientssuch that the nutritional profile of the dish is optimised. 4.3 Meat, fat content and disease Regular consumption of red meat is associated, epidemiologicall y with increased risk of coronaryheartdisease,dueto its fat composition. Conversely a growing bankof evidenceis showingthata healthy diet that includes leanred meatcanproducepositiveblood lipid changes(Wattset al., 1988;Scottet al., 1990; Davidson et al., 1999; Beauchesne-Rondeau et al., 1999). Blood cholesterol levels are increased by inclusion of beef fat, not lean beef in an otherwise low-fat diet. Equal amountsof leanbeef,chicken,andfish addedto low-fat, low-saturated-fat diets, similarly reduce plasmacholesterol and LDL- cholesterol levelsin hypercholesterolaemic andnormocholesterolaemicmenand women. Meatis a sourceof arachidonic acid(20:4n-6), bothin thelean andvisible fat components(Duo et al., 1998).Assumptions that the 20:4n-6content of meat was responsible for increasingthrombotic tendenciesin Westernsocietiesare too simplistic. The presence of large amountsof linoleic acid (18:2n-6) in currentdiets resultsin plasmaincreasesof linoleic andarachidonic acids only. However, in the absenceof linoleic acid, the long chain n-6 and n-3 PUFAs present in lean meat can influence the plasma pool, increasing plasma eicosatrienoic acid (20:3n-6), 20:4n-6, and eicosapentanoic acid (20:5n-3), and probably reducingthrombotic tendencies.It is the imbalanceof n-6: n-3 PUFAsin the diet, brought aboutby excessive 18:2n-6 that causes high tissue 20:4n-6 levels,soencouragingmetabolism to eicosanoids, (Sinclairet al., 1994; Mann et al., 1997). Meatcontributesbetween one-third to half of theUK daily cholesterol intake, (Chizzolini et al., 1999;British Nutrition Foundation, 1999).Meat’scholesterol contentis, for consumers,anothernegative influence on meat’shealth image, althoughit is nowacceptedthatdietaryintakeof cholesterolhaslitt le bearingon plasma cholesterol. A review of the cholesterol content of meat indicates surprisingly that levels of cholesterol are generally not higher in fatty meator meatproducts. The cholesterolcontentof a meat is related to the number of musclefibres so tendsto be higher the morered the muscle. Twenty years ago red meat and meat products were identified as major contributorsto fat intakein theUK. Most of thevisible (subcutaneous)fat in the meat was consumed. In the early 1980sthe red meat industry beganto shift production systems to favour less fat, reflecting more energyefficient animal The nutritional quality of meat 69 husbandry. For many years now therehasbeenemphasis on reducing the fat content of our diets and this continued consumerdemandfor less fat, further promptedthe meatindustryto considerways to reducethe fat contentof meat. The fat contentof the carcasshas reducedin Britain by over 30% for pork, making British porkvirtually theleanestin theworld, 15%for beef, and10%for lamb, with further reductions anticipatedfor beefandlamb over the next 5–10 years.The fat contentof fully trimmedlamb,beefandpork is now 8%, 5% and 4% respectively (Chanet al., 1995). Theseachievementsare due to three factors: selectivebreedingand feeding practices designedto increasethe carcasslean to fat ratio; official carcass classificationsystemsdesignedto favour leanerproduction;andmodernbutchery techniques(seamingout wholemuscles,andtrimming awayall intermuscularfat. It is easierto appreciatethe processandextentof fat reductionby looking at the changesover time for a single cut of meatsuchas a pork chop (Fig. 4.1). The reductionin fat for pig meatis well illustratedby the trenddownwardsin P2 fat depthfrom the 1970sto the 1990s(P2 is fat depthat the positionof the last rib) (Fig. 4.2). Since1992it hasremainedstableat around11mm. Although updated compositional figures for British meat were published from 1986onwards (Royal Societyof Chemistry, 1986;1993; 1996; Meat and Sourcesof data: McCance and Widdowson (1940, 1960, 1978); Royal Society of Chemistry(1995);MLC/RSC report to MAFF (1990). Fig. 4.1 Pork loin – changein fat contentof pork loin for 100gof raw edible tissue. Adaptedfrom Higgs andPratt,1998. 70 Meat processing Livestock Commission andRoyal Society of Chemistry, 1990),it is only since updatedsupplementsto the McCance andWiddowsontableswerepublishedin 1995 (Chanet al., 1995, 1996), that the achievementof the meat industry in reducing the fat content of meat has been more widely acknowledged (DepartmentOf Health,1994a;ScottishOffice, 1996; Higgs,2000). A fat audit for the UK, commissioned by the Government’s Ministry of Agriculture,FisheriesandFood to traceall fat in thehuman food chainprovides a more accurate picture than National Food Survey (NFS) (Ministry of Agriculture, Fisheries and Food, 1981–1999) data for identifying principal sourcesof fat in thediet, between 1982–1992 (Ulbricht, 1995).It illustrates that whereas thefat contributedby redmeatreducedby nearly a third, that from fats and oils as a group increasedby a third to contribute nearly half of our fat intakes(Fig. 4.3). This striking picture is lost in NFS datasincevegetable fats (in particular) areconsumedwithin a broadrangeof endproducts– from chips (so hidden within the vegetables section) to meat products (so artificially inflating the apparent fat contributedby meat). The fat content of meat productscan vary considerably,dependenton the proportionof leanandfat presentandthe amountof addednon-meatfat (Higgs and Pratt, 1998). Traditional types such as sausages,pastry-coveredpies and salamiarehigh in fat (up to 50%) but modernproductsincludereadymealsand preparedmeatsthat canbe low in fat (5%). The trenddownwardsin fat for red meatis reflectedin thereducedfat contentof a numberof meatproducts,suchas hamsandsausages.Somereducedfatmeatproductsarenow availablealthough the potentialfor productdevelopmentin this areahasnot beenfully exploited. 4.4 Fatty acids in meat The fatty acid compositionof food, including meat, has becomeincreasingly important in recent years,becauseof concernswith the effects they have on Fig. 4.2 AverageP2 fat depthof British slaughterpigs 1972– 95.Source:MLC (1990). The nutritional quality of meat 71 human health. Fatty acids play a role in many conditions such as CHD, cancer, obesity, diabetes and arthritis. These roles can be protective, causative, or relatively neutral, depending on the disease, the fatty acid, and the opposing effects of other dietary components. Current dietary advice emphasises balancing the intake of the different fatty acids. The Department of Health (COMA, 1994) has recommended a reduction in the intake of saturated fat and an increase in the intake of unsaturated fat. Within the unsaturated fatty acids it is recommended to increase the omega-3 (n-3) PUFAs relative to the omega-6 (n-6) PUFAs. 4.4.1 Saturated fatty acids Probably the main misconception about meat fat is that it is assumed to be totally saturated. Meat contains a mixture of fatty acids both saturated and unsaturated and the amount of saturated fat in meat has been reduced in recent years. Nowadays, less than half the fat in pork and beef and 51% of the fat in lamb is saturated. The saturated fat contributed to the diet from red meat and meat products has gradually fallen from 24% in 1979 to 19.6% in 1999. Carcass Fig. 4.3 Total fat availablefor consumption(UK) from different food sources.Adapted from: Ulbricht 1995fat in the food chain. 72 Meat processing meatsnow provide 6.7% of total saturatedfat intake (Ministry Of Agriculture FisheriesAnd Food,1981). In reality eventhis figure is an overestimate,since there is a disproportionate wastage in terms of trimming, cooking losses and platewaste (Leedset al., 1997). The predominant saturatedfatty acids in meat are stearicacid (C18:0) and palmitic acid(C16:0). In

general terms,saturatedfatsareknownasthe‘bad’ fats asthey tendto raiseblood cholesterolandcauseatherosclerosis.However, not all saturatedfats are equal in their effectson blood cholesterol. For instance, stearicacid doesnot appearto raiseblood cholesterol(Bonanome andGrundy, 1988)or other thrombotic risk factors(Kelly et al., 1999,2001).Stearic acidis a prominentsaturatedfat in meat,for example, it accountsfor approximately one- third of the saturated fat in beef. Similarly, palmitic acid, another major saturatedfat in meatdoesnot consistently raiseblood lipids. On theother hand, myristic acid (C14:0) is the most atherogenic fatty acid, it hasfour times the cholesterol-raising potential of palmitic acid (Ulbricht and Southgate, 1991). Myristic acid is found only in minor quantities in meat. 4.4.2 Monounsaturated fatty acids Meat containsa mixture of unsaturated fatty acids, polyunsaturated fatty acids and monounsaturated fatty acids (MUFAs). MUFAs are the dominant unsaturated fatty acid in meat and they account for approximately 40% of the total fat in meat.It is a neglectedfact thatmeatandmeatproductsarethemain contributorsto MUFAs in theBritish diet, supplying 27%of total MUFA intake (Ministry Of Agriculture Fisheries And Food, 1999). MUFAs areconsidered to beneutral with respect to bloodcholesterollevels. The principal MUFA in meat is oleic acid (cis C18:1n-9), which is also found in olive oil and is associated with the healthyMediterraneandiet. 4.4.3 Polyunsaturated fatty acids The PUFAs have a structural role as they are found in the membrane phospholipids andtheyarealsoinvolved in eicosanoid synthesis.Therearetwo typesof polyunsaturatedfatty acids, the omega-3(n-3) andthe omega-6(n-6). Meatandmeatproducts,supply 17%n-6 and19%n-3 PUFA intake(Gregoryet al., 1990). Linoleic acid (C18:2 n-6) and -linolenic acid (C18:3n-3) are essential fatty acids as we cannot synthesise them ourselves, so we are dependent on diet to provide them.In the body these arefurther elongatedand desaturated to longer chain derivatives, arachidonic acid (C20:4n-6), docosapentaenoic acid (C22:5n-6), eicosapentaenoic acid (C20:5n-3) and docosahexaenoicacid (C22:6n-3). Thesearefound in usefulquantities in meat. Overthepast30 years therehasbeena majorshift in theintakesof thedifferent fatty acids,thesaturatedfatsbeingreplacedby theunsaturatedfats.The increase in theunsaturatedfatty acidswasmainly dueto anincrease in n-6 fatty acidsas a consequenceof replacing vegetable oils for animal fat. Today, the usual The nutritional quality of meat 73 Westerndiet contains10 to 20 times moren-6 thann-3.For instance, in theUK, the n-6 PUFA intake is now responsible for 87.5% of total PUFA intake, the remainderbeingthen-3 PUFAs. However, evidencenow indicatesthat it is the n-3 PUFAs which are cardioprotective, in particular, the very long chain n-3 PUFAs, eicosapentaenoicacid (C20:5n-3) and docosahexaenoicacid (C22:6n- 3). The GISSI trial showed that 1g of eicosapentaenoic acid (C20:5n-3) and docosahexaenoicacid(C22:6n-3)daily reducedcoronaryheart diseasedeathsby 20% (GISSI, 1999).The exactmechanism for this effect is not clear but they mayreducebloodcholesterol.Otherbeneficial effectsof thevery long chainn-3 PUFAs include anti -inf lammatory and anti -tumourigenic properties. Docosahexaenoicacid (C22:6n-3)also plays a role in neuronaldevelopment, cognitive function and visual acuity. It appears that newbornbabieshave a reduced ability to make the longer chain derivatives anddocosahexaenoic acid (C22:6n-3) is anessentialfatty acid for thenewborn.Meatandfish aretheonly significant sourcesof preformed very long chain n-3 PUFAs in the diet. The chief sourcesof n-3PUFAsareoily fish andfish oils, however,only one-third of theUK populationconsumeoily fish weekly. Not sosurprisingthenin theUK, meat andmeat productssupply moren-3PUFAs(19%)thanfish andfish dishes, (14%) (Gregory et al., 1990).In a reporton n-3 fatty acidstheBritish Nutrition Foundationsummarisedthis fact with thefollowingstatement ‘red meat is likely to rival fish asa source of n-3 PUFAsin many peoplesdiet’ (British Nutrition Foundation, 1999). Animals can convert -linolenic acid to 20and 22-carbonn-3 PUFAsbut plants cannot,hence, thereareno long chainPUFAsin vegandiets.Diets that excludemeatand fish, suchasvegetariandiets,arepractically devoid of very long chainn-3 PUFAs. Vegansrely solely on the endogenoussynthesis of very long chainn-3 PUFA from -linolenicacid.This fact is verified by studies that haveshown that vegetarianshavelower n-3 PUFA intake than their omnivore counterparts.This imbalancemayhavenutritional consequences for vegansand vegetarians.For instance, results from a recent observationstudy showed that the n-3:n-6 ratio in plasmaphospholipids was significantly lower among ovo- lactovegetarians and vegans compared with meat eaters and this may be responsiblefor an increased platelet aggregationtendencyamongvegetarians, which is a risk factor for cardiovasculardisease,(Li et al., 1999). Meat is alreadya valuable sourceof n-3 PUFAsamong omnivores,thusany further increase in then-3 PUFA contentof meatwill make useful contributions to their overall intakes. Nowadays, researchersare looking at waysto enhance the n-3 PUFA contentof meat. Feedingtrials of cattle, pigs and sheephave shown dietary modification to besuccessful in raisingn-3PUFAcontentof their meats.Then-3PUFAcontentof meat canbeenhancedby increasingtheamount of n-3 PUFAs in thediet of theanimal.For instance,grass is rich in -linolenic acid (C18:3n-3)and grassfed meat has a higher n-3 fatty acid content than grain-fed meat (Enser et al., 1998). Similarly, experiments have shown that including fish oil, marinealgae,oils andoilseeds,suchaslinseed, which arerich sources on n-3 PUFAs, in the animals’ diet can favourably enhance the n-3 74 Meat processing contentof theresultantmeat. Enhancing then-3 PUFA contentof meatis much easierto achievein monogastrics,suchaspigsandpoultry, thanin ruminants.In the rumen, the dietary unsaturated fatty acids are susceptible to biohydrogenation. Biohydrogenation is a processthat occurs in the rumen wherethe dietary unsaturated fatty acidsarehydrogenatedby ruminant micro- organisms to more saturatedend products. Evidence indicates that some unsaturated fatty acids appear to be more resistantto biohydrogenation than others. Examples include the very long chain n3 PUFAs. However more research is required to clarify this issue.Researchers are looking at ways to overcome biohydrogenationin ruminants by protectingthe n-3 PUFA. Altering the fatty acid composition of meat can have negative impacts on the meat quality, its shelf-life, colour and flavour. Therefore animal scientists, food technologists and nutritionists are looking at ways to improve the nutritional quality of meat by enhancingits n-3 PUFA contentwithout causinganyadverse sensory qualities or negativelyaffecting its shelf-life. The Department of Health (1994a) has issued guidelines regarding the recommended intake of saturated and polyunsaturated fats. The current recommendation for the polyunsaturated:saturatedratio (P:S ratio) is about 0.4.Porkhasa positive P:Sratio whereas theP:Sratio of lambandbeefis lower (Table 4.1), asa consequenceof biohydrogenation.The Department of Health (1994) has also issued an index regarding the ratio of n-6:n-3 PUFAs. The recommendedvaluefor this ratio (n-6:n-3) is lessthan4. The n-6:n-3ratiosof trimmed beef, lamb and pork are approximately 2.2, 1.3 and 7.5, respectively (Table 4.1). Therefore, both beef and lamb have acceptable n-6:n-3 ratios whereas that for pork needsto be reduced, to reach acceptable values. The reasonfor thehigh n-6:n-3ratio in pork, is dueto significant amountsof linoleic acid (C18:2 n-6) presentin its adiposetissue(Enser et al., 1996).In summary, researchersare focusing on ways of enhancing the n-3 PUFA content of meat andmeat products. However, when increasing then-3 fatty acidcompositionof ruminant meatssuchasbeefandlamb,theyarefocusing on waysto increasethe P:S ratio whilst retaining the positive n-6:n-3 ratio. On the other hand, for monogastric meat, such as pork, the n-3 PUFA contentshould be increased, whilst maintaining its positive P:S ratio. Many of the results to date are promising, for instance,beef and lamb liver from animalsraisedon grass are particularly goodsourcesof n-3PUFAswith then-6:n-3being0.46 (Enseretal., 1998).Suchdatahighlights the potential for carcassmeatwith improved fatty acid composition as a highly acceptable and effective vehicle for providing optimal fatty acid intake for the consumer. 4.4.4 Conjugated linoleic acid (CLA) Another emerging dietary benefit for meat, in particular, ruminant meat, is conjugated linoleic acid (CLA). CLA is a fatty acid that occursnaturally in ruminant meatssuchasbeefand lamb. The acronymCLA is a collective term usedto describe a mixture of positional(7,9-; 8,10-;9,11-;10,12-or 11,13-) and The nutritional quality of meat 75 geometrical (c,c-; c,t-; t,t- or t,c-) isomersof linoleic acid (9c,12c-18:2). CLA hasthe samechain lengthaslinoleic acid (18C),but in CLA the double bonds are conjugated. Conjugated double bonds are separated by only one single carbon bond.The c9-t11-18:2isomer(rumenic acid) is the predominantisomer of CLA (Krameretal., 1998).This isomerhasbeenshown to account for at least 60% of total CLA in beef (Shanthaet al., 1994;O’Sheaet al., 1998).Factors influencing the CLA contentof meat include the breed,age and diet of the animal (O’Sheaet al, 1998; Mulvihill, 2001). As well as having a high n3 PUFA content, grassfed meat also has higher CLA content (Shanthaet al., 1994).Since,CLA is formedpredominately in the rumen,the CLA contentof ruminant meat, beefandlamb, is much higherthannon-ruminant meat suchas pork, chickenandgame (Chin et al., 1992).The bestnatural dietary sourcesof CLA areruminant productssuchasbeefandlamb (Ma et al., 1999).Meat and meat products supply approximately a quarter of dietary CLA in Germany (FritscheandSteinhart,1998). CLA appears to havea variety of potential health benefits. It hasbeenshown to have tumour-reducing (Belury, 1995; Ip et al., 1991, 1994, 1999; Ip and Scimeca, 1997) and atherosclerotic-reducing properties (Lee et al., 1994; Nicolosiet al., 1997;Gavinoet al., 2000).CLA mayalsoreduceadiposity (Park et al., 1997;Westet al., 1998)anddelaythe onsetof diabetes(Houseknechtet al., 1998). The different isomers of CLA appearto be responsible for its differing biological effects.For instance, the c-9,t-11 isomermay play an anti- carcinogenicrole, while the t-10,c-12 isomerappears to play a role in reducing adiposity.Sofar, mostof theresearchwork demonstrating thehealthbenefitsof CLA hasbeenconducted in experimental animalsor cell culture models. The jury is still out for its effect on human health. The American Dietetic Associationhasendorsedbeefandlambasfunctionalfoodsbecauseof theanti- tumourigenic properties of the CLA they contain (ADA, 1999). We are just beginning to fully understand the effect(s)that CLA hason human healthand the role that meat plays in its dietary provision. In a review, Mulvihill (2001) Table 4.1 Fatty acid ratiosrelatedto healthynutrition Sourceof meat Sample P:S n-6:n-3 Beef Muscle 0.11 2.11 Beef Adiposetissue 0.05 2.30 Beef Steak 0.07 2.22 Lamb Muscle 0.15 1.32 Lamb Adiposetissue 0.09 1.37 Lamb Chop 0.09 1.28 Pork Muscle 0.58 7.22 Pork Adiposetissue 0.61 7.64 Pork Chop 0.61 7.57 Valuesfor steaksandchopscalculatedfor whole cut aspurchased. Adaptedfrom Enseret al. (1996). 76 Meat processing raiseda numbera questions thatneedto beansweredto improve our knowledge aboutCLA in meat.They include: howis CLA

formedin therumen?Can thisbe regulated?What CLA isomers are in meat?Can meatconsumption influence CLA levels in the humanbody? 4.4.5 Trans fatty acids Trans fatty acids raiseLDL cholesteroland decreaseHDL cholesterol. It is recommended by the Departmentof Health (1991) that trans fatty acids contribute lessthan2% of total energy.Ruminantmeatsarea sourceof trans fatty acids,contributing around18%of total intakes.Theseareformedduring biohydrogenationin the rumen.In the British diet the main sourceof trans fatty acids arecereals andcereal productsandfat spreadswhich usepartially hydrogenated vegetableand fish oils in their products. Other significant sourcesinclude ruminant meatandmilk (Gregoryet al., 1990).It appearsfrom the analysisof 14 Europeancountries that the fat contentof meat doesnot correlatewith thepercentageof trans fatty acidcontent(Hulshof et al., 1999). Transfatshavebeenhighlightedascontributingto atherogenesis,althoughthe hydrogenated fats from vegetablesourcesused in bakery goods and other processedfoods appearto be more of a concernthan the natural trans fats found in ruminant meatsand milk fat (British Nutrition Foundation’sTask Force,1995). After assessing the intake of trans fatty acids in 14 European countries (TRANSFAIR study), the conclusion wasthat the currentintakeof TFA in mostWestern Europeancountriesincluding theUnitedKingdom does not appear to be a reasonfor major concern(Hulshof et al., 1999; van de Vijver et al., 2000). In fact, the TRANSFAIR study,showedthat intakesof trans fatty acids did not influence LDL and HDL cholesterol and a weak inverseassociationwasfound in total serumcholesterol(van de Vijver et al., 2000). In the USA, there is a much greater relianceon processed foods, the consequenthigher intakes (6% dietary energy)of non-ruminant trans fatty acidsarecausingsomeconcern. 4.4.7 Cholesterol Much researchhaslookedat theeffect that individual fatty acidshaveon blood cholesterol rather than the mixture that we digest. It is now obvious that we shouldbe looking at the effect that diet asa whole hason blood cholesterol. In the United States, the National Cholesterol Education Program (NCEP) recommendsdietary guidelines for people with hypercholesterolaemia (raised blood cholesterol). The NCEPdietary guidelinesarea first-line therapyfor the management of high blood cholesterol. A recentstudy comparedthe effect of including leanred meat (beef,veal andpork) andleanwhite meat(poultry and fish) in the NCEP diet, on blood cholesterol of people with hyper- cholesterolaemia (Davidsonet al., 1999).This study showedthat the inclusion of approximately170gleanredmeat perday,five to seventimesperweekin the The nutritional quality of meat 77 NCEPdiet wasaseffectiveasleanwhite meatin reducing both total andLDL cholesterolwhile simultaneouslyraisingHDL cholesterol. Thusthe inclusionof lean red meatin sucha diet hada positive impacton blood cholesterol levels. Theauthorsalso indicatedthatthestudy participantswhoconsumedtheleanred meat weremore likely to follow their dietary regimenasthey hada wider food choice than those on the white meat diet. This study not only highlights the nutritional valueof redmeatin suchadiet but alsothepracticalvalue,asno diet canpossibly work unlessit is adhered to! An earlier studyconducted in the United Kingdom, showedsimilar results, where mildly hypercholesterolaemic men ate 180g of lean meatevery day, a quantity we would considerhigh today.This diet waslow fat, low saturated fat and high in PUFA and it proved to be effective in lowering total and LDL cholesterol(Watts et al., 1988). In Canada,a study was conducted comparing the effects of lipidlowering diets containinglean beef, poultry (without skin) andleanfish on plasmacholesterol levelsin menwith raisedbloodcholesterol. The results indicatedthat when comparedto the usualdiet, the lean beef and poultry diets significantly reduced both total cholesterol and LDL (‘bad’) cholesterolin menwith raisedbloodcholesterol.Whereas, in thefishcontaining diet, only total cholesterollevels fell significantly when comparedto the usual diet (Beauchesne-Rondeauet al., 1999). There is now a wealth of studies showing similar results (Scott et al, 1990; Mann et al, 1997; Davidson et al., 1999),which arenot that surprising, asleanred meat is low in fat, low in SFA and containsa mixture of beneficial unsaturated fatty acids,such as linoleic acid, n-3 PUFAs,MUFAs andCLA. 4.5 Protein in meat Protein is the basic building material for making cells and its adequateintake canbeof particular benefitfor thosegrowing or in adultswheremuscle tissueis being rebuilt, suchasathletesor those recuperating postsurgery. Meat is a good source of protein and it contains all the essentialamino acids. In the United Kingdom, meat and meat products supply 30% of dietary protein intakes (Ministry Of AgricultureFisheriesAnd Food,1999).Emphasison a prudent diet for health that recommendedjust 11E% (National Advisory Committee On Nutrition Education,1983) from protein has led us to underplay the potential role of high protein foodsin the diet. Recentinterest in the useof high protein diets(25E%) for weightreduction haveutili sedthehighersatiatingpropertiesof protein, important for dietary compliance, and achievedsignificantly more weight lossover a six monthsdietary intervention compared to lower (12E%) protein. Theseresults were achievedwithout adverseeffects on renal function (Skov et al., 1999a,b). Meat protein hasa higherbiological valuethanplant protein assomeof the amino acids are limi ting in plant protein. For example, lysine is the limiting aminoacidin wheat,tryptophanis thelimit ing aminoacidin maizeandsulphur- 78 Meat processing containing aminoacidsarelimiting in soyabean. It is necessaryfor vegansand vegetarians to eat a wide variety of vegetable protein foods to provide the necessary amountsof eachaminoacid. Meat is a rich source of taurine. Taurine is consideredto beanessential aminoacid for newborns, astheyseemto havea limit ed ability to synthesise it. Taurine concentrations in the breastmilk of veganswere shown to be considerably lower than in omnivores (Rana and Saunders, 1986).The significanceof this finding is unknown. 4.6 Meat as a ‘functio nal’ food Typical Western omnivorous diets over the last 40 yearshavebeenrelatively high in protein andfat with insufficientdietaryfibre, fruit andvegetables.Meat intake is by definition the key differencebetween vegetarian and omnivorous diets,thuscomparative studieshavetendedto exaggeratethehealth benefitsof a vegetarian diet soreinforcing a negativehealthimagefor meat. It haslong been recognised (Burr, 1988) that although vegetarianism seemsto confer some protection againstheartdisease, it is not clear if this is dueto abstinencefrom meator high consumption of vegetables.Meat intakehasprovideda markerfor a generally ‘unhealthy’ diet, in the past(AmericanDietetic Association,1993; COMA, 1991;Sanders andReddy,1994;Thorogood et al., 1994).Furthermore, vegetarianshavetendedto be more healthconscious, they traditionally smoke less,consumelessalcohol, tea,andcoffee,andtendto exercisemore,thustheir goodhealth could be attributed to any or a combination of thesehabits.CHD andcancer aremultifactorial,diet is onefactorplaying a role in theseconditions, but diet aloneis a very broadterm,becausewithin diet thereareprotective and causative factors.Comparing current omnivorous and vegetarian diets shows that the meatcontent of the former is not responsiblefor its higher fat content. Australian researchhas shown that when the meat component was removed from an omnivore diet, the remaining part of the diet was still significantly higherin total fat, saturated fat andcholesterolthana vegetarian diet (Li et al., 1999).This suggeststhat the overall diet ratherthanthe meatis responsiblefor thesediet characteristics. Thesignificanceof meatto nutrientintakedependson theimportancegivento meatin anindividual’s,or society’sdietandculture.With a limited rangeof foods availablein primitive societiesthroughouthistory,meatprovideda concentrated sourceof a wide range of nutrients (Davidsonand Passmore,1969; Sanders, 1999). Consideringthe diet of modern man, where meat is excludedwithin traditional vegetariancultures,the nutrientsit providescan be suppliedfrom a combinationof otherfoodsandthis appearsat leastadequate,providedthediet is not too restrictiveanddependenton nutritionally inferior staplessuchasmaizeor cassava(Sanders,1999). With the rangeand abundanceof foods available to developedsocietiestoday,thenutritionalsignificanceof anyonefood is reduced. Traditionally, the vegetarianwas likely to consumea wider rangeof foods than the meat eater.Consequentlyvegetariansin Europeand North America The nutritional quality of meat 79 historically had similar energy intakes to meat eatersand greaterintakesof vitamins B1, C, E, folic acid,carotene,potassiumandfibre (Sanders, 1999). Nowadays vegetarianismcannotbe assumed to providea favourable fatty acid intake. Comparative studiesof vegetarian and omnivorous children surveyed from 9 to 17 years found that saturatedfat intakes were no lower in the vegetarianchildren (Nathanet al., 1994,1997; Burgess et al, 2001).Therewas nosignificant differencebetweenenergyintakesandthepercentageenergy from fat, or saturated fat intakesbetween vegetarian and omnivore adolescentsin North WestEngland (Burgesset al., 2001).Vegetarianwomenhavelower zinc intakesandstatusthantheir omnivorecounterparts(Ball andAckland,2000).A recent study in Australia showed vegetarianshad a lower intake of beneficial very long chain n-3 PUFAs (Li et al., 1999). A study comparing meat eaters with vegetarians has shown that plasmahomocysteine,an independent risk factor for heart disease, among vegetarians was significantly higher than their omnivore counterparts,and this was correlated with a lower intake of vitamin B12 amongthevegetarians (Mannet al., 1999;Krajcovicova-Kudlackovaet al., 2000;Mann2001b). Veganshavesignificantly lower intakesof protein,vitamin D, calcium, and selenium but no difference in energy and iron intakes to omnivores and the vegans have significantly lower vitamin B12 blood concentration (LarssonandJohansson,2001). Modern eating habitsarecontributing to erosion of the traditionalvegetarian diet in developedcountriesasthereis now a greater dependenceon vegetarian convenience foods, coinciding with increasedavailability and choice. Whilst vegetarianconvenience foodsmayappear attractive in termsof healthaswell as for easeandspeedof preparation, theyarenot necessarily of superior nutritional valuecompared to meat containingequivalents.Thereis widevariationin thefat content of vegetarian products, ranging from 2% to 58%, with nearly a third supplying more than50% of their energyfrom fat (Reid andHackett, 2001). Excluding meat whilst paying li ttle attention to selecting appropriate alternativefood combinations to ensure adequate nutrientsaresupplied is cause for concern, especially in childrenandadolescents.Today’sbusylifestylesgive rise to more erratic dietary practices making it easierto obtain all nutrients requiredfor healthby includingmeatasa componentof thediet.Thetime spent planning and preparingmeals is minimal and an increasing proportionof our daily food intakeis consumedoutside thehome,assnacksandquickmeals. NFS data suggestthat in 1998, 28% of total expenditure on food and drink was outside the home (MAFF, 1999). Data on the dietary intakesand nutritional status of youngpeople aged4–18yearsin the UK showthat energy intakesof young people are

now approximately 20% below estimated average requirements(EAR) for age.Growthpatternssuggest suchintakesareadequate andmerely reflect the corresponding lower activity levelsof youngsters today, which in itself is a concern. Reducedenergy intakesmust increase theemphasis on a morenutrient densediet, particularly in growing children.The surveyhas recorded intakesof iron, zinc and copperbelow the RNI particularly in older girls (Gregoryet al., 2000).It is possible that the recordedlower meatintakes 80 Meat processing are partly responsible for this. The decision to becomevegetarian should be accompanied by adequate nutritional information and education. Despite popular opinion, vegetarianism per se does not guarantee a nutritionally adequate diet. Conversely, using meatasa significantprotein source in the diet provides a concentrated nutrient supplement, thus ensuring the diet is nutritionally adequate (Department Of Health, 1994; Mill ward, 1999). The potentialfor producing nutritionally superior,convenienceproducts, thatinclude meat as a functional ingredient, is enormousand deservesmore thorough exploitation. 4.6.1 Meat and paleolithic diets Humansareomnivores.Evidencesuchasdentition, gut structureandecosystem, enzymic rangeand adaptability and our dependenceon both plant and animal sourcesfor our essentialnutrientsareall supportive of this issue.We beginlife as omnivores, because as babies in utero, all the nutrientswe receiveare of animalorigin. During theIceAge, plantscouldnotgrowthusmanhadto depend on meatashis main source of nutrition. There is muchhistorical evidenceand datafrom carbon isotopes, gut morphology, brain size, cranio-dental features, tools,weaponsandrockartdepictionof huntingall tracetheevolutionof manas an omnivore (Mann,2001a). Thereis considerableweight to the argument that our brainsevolvedbecausewe could eata variety of foods including meat. As we begin the new Millennium, someexperts are looking at the diet of Paleolithic (stone-age) man in a searchfor ways to reduce the incidences of ‘modern’ diseases suchasobesity, cancerandcoronary heart disease. Research from huntergatherersocieties has indicated that thesepeople were relatively freeof manyof thechronic anddegenerative diseasesthat plagueus today, this is in part, attributable to the different dietary practices.Investigation of the dietary habits of modern hunter-gatherer societies, as an approximation of Paleolithic practices, hasshown a high relianceon animalfoodscomparedwith plant foods for basic energy requirements(Cordain et al., 2000). It hasbeen estimatedthatthehunter-gatherersobtainedapproximately 45–65%of their total energyintake from meat, which was either huntedor fished (Cordain et al., 2000).It is only with the relatively recentrise in agriculture that humans have begunto consumehigh levels of carbohydrates.This is now recognised as a major contributor of ‘Westernlifestyle’ diseases.We havechanged from a diet high in meat to a diet wheregrains and refined foods dominate.The hunter- gatherer diet was high in protein (19–35%E) and low in carbohydrate (22– 40%E)whereas nowadaysthe oppositeprevails – lower in protein (15%E) and much higher in carbohydrates(55%E) (Cordain et al., 2000). The fatty acid profiles of suchdietsmay havediffered with higher levelsof unsaturated fatty acidsin wild animals,compared to domesticatedfarm animals. StudieshaveshownthatAustralianAborigineshaveshown significant health improvements, including a reduction in blood cholesterol levels, after returning to their natural diets– wherethereis a high relianceon animal foods(O’Dea, The nutritional quality of meat 81 1991). Researchof macronutrient proportions in the diet of hunter-gatherer populations show a clear relationship betweenhigh protein content and the evolution of insulin resistance, which offered a survival and reproductive advantage (Brand-Miller and Colagiuri, 1994). However, the advent of agriculture and the rise of a diet higher in carbohydratehasmeantthat people were unpreparedfor the high glycaemic load and this is responsible for the current incidence of non-insulin dependent diabetesmellitus (Brand-Mil ler and Colagiuri, 1994). However, we must also remember that humans are not carnivores and thus we cannotexist on protein intakesabove35% energy for extendedperiodsof time. ‘A clear role for lean red meatin a healthybalanced diet becomes evident as the diet history of our speciesis uncovered’ (Mann, 2001a). 4.6.2 Meat and satiety The prevalenceof obesityhasincreased dramatically in recentyears (National Audit Office, 2001). Satiety influences the frequency of meals and snacks, whereas,satiationinfluencesthesize of mealsandsnacks. Macronutrientshave differing effectson satiety, protein is more satiating thancarbohydrates which are more satiating than fat (Hill and Blundell, 1986; Barkeling et al., 1990; Stubbs, 1995).Theexactmechanismby which protein exertsits satiatingeffect is not known, but it may involve changes in the levels and patterns of metabol i tes and hormones (e.g. amino acids, glucose and insul in), cholecystokinin and amino acid precursors of the neurotransmitters serotonin, noreadenaline anddopamine. A meatcontaining mealwasshownto havemore sustainedsatiety thana vegetarian meal (Barkeling et al., 1990).Otherstudies have shown that different meats have different satiating powers (Uhe et al., 1992).Thesedifferencesmayberelatedto differencesin aminoacidprofilesor digestibilities. More research on the effectsthat differentmeatshaveon satiety will prove invaluable in assessingwhetheror not meat can, in the future, be promotedasa food that cannegatively curb the growing levelsof obesity. 4.7 Meat and micronutrients 4.7.1 Iron in meat Iron deficiency(Schrimshaw, 1991)andiron deficiencyanaemia (Walker, 1998) remain the most common nutritional disorders in the world today. Iron deficiency is the only widespread nutrient deficiency occurring in both developedand developing countries. Iron deficiency affectsbetween20– 50% of theworld’s population(BeardandStoltzfus,2001).Therearemany causes of iron deficiency, including hook worm infestation, low iron intakes, low bioavailability of dietary iron and increased demand due to physiological requirements.The mostcommonresult of iron deficiency is anaemia.Some of the liabilities associated with iron deficiency and anaemia are defective 82 Meat processing psychomotor development in infants, impaired education performance in schoolchildren, adverseperinataloutcomein pregnancy and diminishedwork capacity(Cook, 1999).All of theiron in ourbodycomesfrom ourdiet,andmeat is a rich dietary source.Concern aboutiron deficiencyis onenutritional reason for recommending eatingat leastsome meat(WHO, 1990;COMA, 1998). Food iron can be classifiedas haemiron or non-haem iron. Haem iron is derived from haemoglobin and myoglobin and its chief food source is meat, whereas non-haemiron is derivedmainly from cereals, fruits and vegetables. Meat is distinctive as it contains both typesof iron, haem(50–60%) and non- haem.Our bodiesreadily absorb haemiron (20–30%) as it is not affectedby otherdietary factors.Meatpositively influencesthebioavailability of non-haem iron. Bioavailability of iron refers to the proportion of ingestediron that is absorbedand utilised by the body (O’Dell, 1989). Only two dietary factors enhance non-haem iron bioavailability, they are vitamin C (Hallberg et al., 1989) and meat (Cook and Monsen, 1999; Taylor et al., 1986; Hazell et al., 1978; Kapsokefalouand Mill er, 1991, 1993, 1995; Mulvihil l and Morrissey, 1998a,b; Mulvihil l et al., 1998). Absorption of non-haem iron from meat is typically 15–25%, comparedwith 1–7% from plant sources (Fairweather-Tait, 1989).Thepresenceof meatin a meal enhancesthebioavailability of non-haem iron contained in the other foodspresent suchascereals, fruits andvegetables. Theenhancing effect of meaton non-haemiron bioavailability is commonly referredto asthe‘meatfactor’. Theexactmechanismby which the‘meatfactor’ works still remains unknown despite the fact that numerous efforts have concentratedon this topic. Research indicatesthat the mechanism of the ‘meat factor’ may not be due solely to a single factor but due to a number of contributing factors which work together promoting non-haem iron bioavailability. These factors include the release of cysteine-rich small molecular weight peptides during the proteolysis of meat; the ability of these peptides to reduceferric iron to the more solubleferrousiron; the chelation of soluble non-haemiron by thesepeptides and the ability of meat to promote gastric acid secretionand gastrin releasebetter than other food components (Mulvihill, 1996). Glutathione is a tri-peptidecontaining cysteine,andthis is consideredto play a role in the‘meat factor’. However, reducedglutathionerepresentsonly 3% of total cysteinein meatand this is consideredtoo low to have sucha profound positive influenceon non-haemiron bioavailability (Taylor et al., 1986). Elucidation of the mechanism(s)of the ‘meat factor’ is extremely important in the search for more effective waysto improve iron nutrition. Isolation of the ‘meat factor’ will allow the potential to produce stable non-haemiron absorption enhancers which canbe addedto other foods,thus improving iron bioavailability. Meat and meat products provide 14% of iron intake (MAFF, 1999) within this, carcassmeatand meatproducts supply 12.5%of total iron intakes. This figure grossly underestimatesthevalue of meatfor influencing iron status.Meat hasan importantinfluenceon iron bioavailability andthusiron statusdueto its enhancing properties andoverall greater absorption capacity. Low iron intakes The nutritional quality of meat 83 and status are common amongcertain subgroups of the population; toddlers (Gregory et al., 1995; Edmondet al., 1996),adolescents (Nelsonet al., 1993; Nelson, 1996), pregnant women (Allen, 1997) and the elderly (Finch et al., 1998).Datafrom theNationalDiet andNutrition Survey of childrenshowsthat 20%havelow iron storesand8% haveiron deficiencyanaemia(Gregoryet al., 1995). Iron deficiency anaemia among toddlers is often associated with late weaning practices. A Spanishstudy showedthat children who first ate meat before eight months of age showeda better iron statusthan those who were introducedto meatlater thaneight months(Requejoet al., 1999).Anotherstudy showedthat low iron storesin one-andtwo-year old childrenis relatedto a low meat iron intake (Mira et al., 1996). The COMA report Weaning and the Weaning Diet recommends that foods containing haem iron should be incorporated into thedietsof infantsby 6– 8monthsof age.Soft-cookedpuréed meat can be introduced. This goes against the modern trend to delay introduction, the basisfor which appears to be non-scientific. Adolescentshavehighdemandsfor iron to allow for muscledevelopmentand increasedbloodvolumewhile theonsetof menstruationin femalesmakesthem vulnerableto iron deficiency.Half thefemale populationliving in theUK, aged between 15–18years, haveiron intakesbelow the recommended level. This is reflectedby thefact that27%of thatagegrouphavelow iron stores(Gregory et al., 2000).The prevalenceof low iron storesamong adolescent girls in the UK hasbeencited to be as high as 43% (Nelsonet al., 1993).During pregnancy, more lactovegetarians(26%) reported suffering from iron deficiency than omnivores(11%) (Drakeet al., 1999b). Lyle et al., (1992)hasdemonstratedthat

meat supplementswere more effective than iron tablets in maintaining iron status during exercise in previously sedentary young women. Among the elderly, both low iron intakesand low iron statushasbeenshown to increase with age(Finch et al., 1998). Serumferritin, the body’s iron store,is strongly correlatedwith haemiron (Reddyand Sanders, 1990).Bioavailability of iron plays an important role in determining iron status. Studieshaveshownthatdespite thefact thatvegetarians haveeither a similar or a higher iron intake than their omnivore counterparts, their iron statusis lower (Nathanet al., 1996;Ball andBartlett, 1999;Wilson andBall, 1999).Vegetariansshould consumeiron-rich foodsto compensatefor the low bioavailability of non-haem iron from the foods they eat. The importanceof meatin iron nutrition cannotbe overemphasised.The effectsof meat andmeat products on iron nutrition are threefold.Firstly, they area rich source of iron. Secondly, they contain haemiron, which is readily absorbed. Thirdly, they promote the absorption of non-haem in the diet. 4.7.2 Zinc in meat All meats,but in particular beef, areexcellent sourcesof dietary zinc. It takes 41oz.milk, 15oz.tunaor 6½eggsto equaltheamount of zinc in anaverage4oz. portion of beef(Hammock, 1987).On average,meatandmeatproductsaccount 84 Meat processing for a third of total zinc intakes(MAFF, 1999).Zinc absorptionis suppressed by inhibitors suchasoxalateandphytate which arefound in plant foods(Johnson andWalker,1992;Zhenget al., 1993;Hunt et al., 1995). On thecontrary, meat facilitatesthe absorption of zinc – 20–40%of zinc is absorbedfrom meat.For instance,onestudyshowedthatfemaleomnivoreswhohadasignificantly lower zinc intakethantheir vegetarian counterpartshada higherzinc status(Ball and Ackland, 2000), suchdatahighlights the role that meatplays in providing an assuredsourceof dietary zinc. Because of the low bioavailability of zinc from plant foods,vegetariansshould strive to meetor exceed their RDA for zinc, to ensureadequate zinc intakes. Zinc is necessary for growth, healing, the immune system,reproduction (Aggett and Comerford, 1995) and cognitive development (Sandstead,2000). Low zinc intakesarebecoming moreprevalent, especially amongadolescents. An NDNS surveyshowedthatonein ten7–10-year-oldgirls andonein threeof 11–14-year-old girls have intakes of zinc below the recommended level (Gregory et al., 2000). Long-term, low zinc intakeslead to zinc deficiencies, which maybecomea public healthproblemin thefuture(Sandstead,1995).Iron and zinc deficiencies can often occur simultaneously, particularly among adolescents (Sandstead, 2000). Adolescentsoften avoid eating meat; in some incidencesmeat is providing up to just 25% of total zinc intakescomparedto 40% of adult intakes(Gregory et al., 1995;Mills andTyler, 1992;Gregory et al., 2000).Therefore includingmeatin thediet of adolescentscanaid in averting bothiron andzinc deficienciesin concert, asthesemineralsin meatarein easily absorbable forms. Similarly, concern over low zinc status among infants promptedtheDoH, in its COMA weaningreport,to recommendincreasing meat portion sizesfor infant’s at the weaning stage(DepartmentOf Health, 1994b). 4.7.3 Selenium in meat Seleniumacts as an antioxidant and is considered to protect againstcoronary heartdiseaseand certain cancers, suchas prostate.Meat contains about10mg selenium per100g,which is approximately 25%of our daily requirement.Beef andpork contain moreseleniumthanlamb,which maybedueto theageof the animal as selenium may collect in the meat over time. Bioavailability of selenium from plant foods was thought to be greater than that from animal foods, but recent datademonstrate thatmeat, raw andcooked, providesa highly bioavailable source (Shi andSpallholz,1994). 4.7.4 Other minerals in meat Meatalsocontainsphosphorus,a typical serving providesroughly 20– 25%of an adult’ s requirement. Phosphorus has important biochemical functions in carbohydrates,fat andprotein metabolism. Meat also providesuseful amounts of copper, magnesium, potassium,iodine andchloride. The nutritional quality of meat 85 4.7.5 B-vitamins in meat Meat is a significant and an important source of many B vitamins. The B- vitamins in meat are thiamin (vitamin B1), riboflavin (vitamin B2), niacin, pantothenic acid, vitamin B6 and vitamin B12. B-vitamins are water soluble hence, leanmeat contains moreof thesevitaminsthanfattier meat.Somelosses of B-vitamins occurduring cooking,theamount lost depends upontheduration andthe temperature of the cooking method. Thiamin and riboflavin are found in useful amounts in meats. Pork and its products including baconandhamareoneof therichestsourcesof thiamin.Pork containsapproximately 5–10 times asmuch thiamin asbeefor lamb. Thiamin aids the supply of energy to the body by working aspart of a co-enzyme that converts fat and carbohydrates into fuel. It also helps to promote a normal appetite andcontributes to normalnervoussystemfunction.Typical servingsof pork provideall thedaily requirementof thiamin.Offal meatsaregood sources of riboflavin, for example, a single portion (100g) of kidney or liver provides more thanits daily requirement. Riboflavin, like thiamin, alsoaidsin supplying energy andalsopromoteshealthyskin, eyesandvision. Meat is the richest sourceof niacin. Half the niacin provided by meat is derived from tryptophan,which is more readily absorbedby the body thanthat boundto glucosein plantsources.Niacin helps to supply energyto thebodyasit plays a role in converting carbohydrates and fats into fuel. Meat and meat products supply more than a third of total niacin intakes in Britain (MAFF, 1999).Liver andkidney arerich sourcesof pantothenic acid.Althoughmostof this vitamin is leachedinto the drip loss associated with frozen meat, this is unlikely to beof anynutritional consequence aspantothenicacid is universal in all living matter. A 100g portion of veal liver provideshalf our daily vitamin B6 needsand other meatsprovidearound a third. Vitamin B6 is a necessaryco-factor for more than 100 different cellular enzymereactions,including thoserelated to amino acid metabolism and inter-conversion. Vi tamin B12 is exclusively of animal origin asit is aproduct of bacterialfermentation,which occursin theintestineof ruminant animals suchas cattle, sheepand goats. Vi tamin B12 is required to produce red blood cells and acts as a cofactor for many enzymereactions. Deficiency of vitamin B12 causes megaloblastic anaemia, neuropathy and gastrointestinal symptoms.Groupsat risk of vitamin B12 deficiency include vegansandstrict vegetariansbecausevitamin B12 is exclusively of animalorigin and the elderly, becausetheir ability to absorb this vitamin from the diet diminisheswith age(Allen andCasterline, 1994;Swain,1995;Baik andRussell, 1999;Drakeet al., 1999a). In thepastsomevitamin B12 wasprovidedfrom the soil of poorly cleanedfoods. This may in part explain the apparent absence of deficiency in some vegan groups. Today with the emphasis on good food hygiene practices, this source can no longer protect against deficiency in vulnerable individuals. Vegans are recommended to take vitamin B12 supplementssincethe quantityconsumedfrom foodsfortified with the vitamin is too low (Jones, 1995;Draper, 1991:SandersandReddy,1994).The RNI for 86 Meat processing vitamin B12 amongthe elderly is 1.5g/day (Departmentof Health, 1991).A 100gportion of leantrimmed beefcontains 2g vitamin B12, thussupplying all their daily needsfor this vitamin. In Britain, meat and meat products supply morethana fifth of both vitamin B6 andB12 intakes(MAFF, 1999).The need for vitamin B12 has been a part of the rationale for recommending the consumption of animal foodsamong all agegroups(WHO, 1990). Raisedhomocysteine,anaminoacidmetabolite, is anindependent risk factor for cardiovascular disease. It is estimated that 67% of the cases of hyperhomocysteinemiaare attributable to inadequateplasmaconcentrationsof oneor moreof theB-vitaminsnamely;folate, vitamin B6 andvitamin B12. Some enzymesthat reducehomocysteine levels require vitamins B6 and B12 as co- factors. Vitamin B6 is a co-factor for two enzymereactionsthat catabolise homocysteineto cysteine via a transulfuration pathway, they arecystathionine synthase and cystathionase.Meanwhile, vitamin B12 is a co-factor for the remethylation enzyme,methionine synthase, which convertshomocysteine to methionine. Researchhasshown that low levels of both vitamins B6 and B12 independently correlate with raised homocysteine. For instance, ovo- lactovegetariansor veganswho had significantly lower serum vitamin B12 levels thanmeateatershadsignificantly higher levelsof plasmahomocysteine (Mann et al., 1999, KrajcovicovaKudlackova et al., 2000, Mann, 2001b). Similarly, low doses of vitamin B6 can effectively lower fasting plasma homocysteinelevels (McKinley et al., 2001). The role of meat in regulating homocysteineis intriguing andneedsto be addressed further. 4.7.6 Meat and vitamin D In the bodyvitamin D actsasa hormone,essential for theabsorption of dietary calcium. Therefore, vitamin D is essentialfor skeletaldevelopment andsevere deficiency is associated with defectivemineralisation of the boneresulting in ricketsin childrenor its adult equivalent,osteomalacia(Fraser,1995;Dunnigan and Henderson, 1997; DeLuca and Zierold, 1998; Department of Health, 1998b). More subtledegrees of insufficiency lead to increasedbone loss and osteoporotic fractures. Other functions of vitamin D includes its role in the immune system, andmay be protectiveagainsttuberculosis,muscle weakness, diabetes, certain cancersand coronary heart disease (Department of Health, 1998b). It is well establishedthat sunlightexposure on theskin is themainsource of vitamin D. However, therearecertain subgroupsin thepopulationwhoaremore at risk of vitamin D deficiency,andthesedependon diet in addition to sunlight to obtainadequatevitamin D. Suchsubgroupsincludeinfants, toddlers,pregnant and lactating women, the elderly and those who have low sunlight exposure, suchascertainethnic minorities andthosehousebound(Departmentof Health, 1998a). The prevalence of vitamin D inadequaciesamong these groups is widespread.For instance,27%of two-yearold Asianchildrenliving in England have low vitamin D status(Lawson and Thomas, 1999) and, 99% of elderly The nutritional quality of meat 87 people li ving in institutionsarenot receivingenoughof dietary vitamin D (Finch et al., 1998).Vitamin D deficiencyamongthe elderly will become much more apparent and a greaterpublic health problem when we consider that we are living in an increasingly ageingpopulation. Liver aside, meat and meat products were considered poor sourcesof vitamin D. However, new analytical data for the composition of meat indicatesthat this is not true (Chan et al., 1995). Meat and meat products contain significant amountsof 25-hydroxycholecalciferol, assumed to havea biological activity five timesthatof cholecalciferol. In fact, themeatgroupis now recognisedasthe richestnaturaldietary sourceof vitamin D, supplying approximately21%(GibsonandAshwell,1997). Vitamin D is presentin both theleanandthefat of meatalthoughits exactfunction in theanimal is not yet known. Sinceinterestin therole of meatin supplying vitamin D is a relatively new subject, there are certain areasthat needto be researchedsuchas the effect of cooking meat on vitamin D levels, the bioavailability of vitamin D from meatandtheinfluenceof seasonal variation on thevitamin D contentof meat andmeatproducts. Low intakeof meat

andmeatproducts, hasemergedasan independent risk factor for Asianricketsandabsentintakeof meatandmeatproducts emerged as an independent risk factor for Asian osteomalacia (Dunniganand Henderson, 1997). It has beenhypothesisedby this research group that there may be a ‘magic factor’ in meatwhich is protectiveagainstrickets andosteomalacia.In Glasgow, at the beginning of the century, the incidence of rickets was high, whereas,between 1987 and 1991,only one caseof rickets was reported. This may be explained by the fact that nowadaysinfants are weanedonto an omnivorousdiet from four monthsof ageand this meat inclusion is offering protection against rickets (Dunniganand Henderson,1997). Obviously much more researchis required to improveour knowledgeon this subject.It is also of interest to note that signs of both iron and vitamin D deficiency can occur simultaneously among toddlers (Lawson and Thomas,1999). For instance, during thewinter half of thetoddlershadbothlow vitamin D andlow iron levels (LawsonandThomas, 1999).Suchevidencehighlightsthe potential protective role that meat inclusioncanplay in a toddler’s diet. It is importantfor toddlers andchildrento eatfoodsrich in both iron andvitamin D suchasmeat andmeat products aswell asplaying outdoors to get sunlight. 4.8 Future trends As we begin the 21st Century, we look to the future to predict the li kely nutritional problemswe will needto tackle.The four majornutritional problems today areheart disease,hypertension, obesityanddiabetes.Theseare likely to remain significant public health problems in the future. The demographic structureof thepopulation is changing.Throughout Europebothbirth anddeath datesarefalling, peopleareliving longer andit is estimatedthatby theyear2030, 88 Meat processing morethanhalf thepopulationliving in theUK will beover50yearsold.With this knowledgewe shall try to ascertainthe likely future nutritional role of meat. This chapterclearly outlines ways to reducethe fat content of meat and manipulate its fatty acid composition. The meatthat is on saletodayhasnever beenleaner.Fortunately, mostof the valuable nutrientsof meatare located in the leancomponent, so reducingthe visible fat of meathaslittle bearing on its micronutrientstatus. Researchers arefocusingon ways of further improvingthe fatty acid composition of meat,usingtheknowledgethatgrassfeedingresultsin high levelsof bothn-3PUFAsandCLA content.Bothn-3PUFAsandCLA may have many possible benefits for human health, and in particular may offer protection againstpredicted future healthproblems(Cordainet al., 2002).N-3 PUFAs,in particular, havea very long chain,arecardioprotectiveandhaveanti- inflammatoryandanti-tumourigenic properties.CLA canprevent formation and slow thegrowthfor tumourdevelopment(Ip et al., 1994),reduce atherosclerosis development (Lee et al., 1994) and can help normalise blood glucoselevels, which maybeshown to prevent adult-onsetdiabetes(Houseknechtet al., 1998). Studiesin human subjectsareneeded beforewefully realisethebenefitsof CLA on human health.Thefat andfatty acidstoryfor meatsofar is positive andonly research andtime will tell whether this story will be further improved. The prevalence of overweight and obesity is increasingsteadily in many developedcountries. In the UK, over a quarter of the population are either overweight or obese.Obesityis a risk factor for many conditions.During a ten- year follow-up study, the incidence of colon cancer,diabetes,heart disease, hypertension,stroke (menonly) andgallstonesincreasedin line with thedegree of overweightamongadults (Field et al., 2001).Thus,reducingtheincidenceof overweight and obesity is a major public health priority. A positive energy balanceis the causeof practically all casesof overweightandobesity. Factors regulating food intakearehunger, appetite,satiation andsatiety. Meat-containingmeals havehighersatietyvaluesthanvegetable-containing meals(Barkeling et al., 1990).Research needsto be undertakento determine whether meatcanplay a role in curtailing obesity,asa resultof its high satiety value.MediahypeaboutCLA hasconcentratedon its ability to reducebodyfat and increaselean body mass. Studies havenotedthat CLA inducesa relative decreasein body fat andan increase in leanmuscle(Parket al., 1997;Westet al., 1998). Trials are currently under way to confirm whether or not these benefitsoccur in humans.Leanmeat alreadyis low in fat, but otherattributes suchasits high satietyvalue andtheCLA it containsmaybeusedin the future to market meat as a food than can help to reduce overweight and obesity. Furthermore, the capacity of meat to encourage greater vegetableand salad consumption, dueto theway it is eatenshould not be overlooked in this regard. An increase in the incidence of hip fracturesis an inevitable consequence of people living longer. Researchhas shown that an increase in meat protein consumption among elderlywomencorrelateswith a decreasein the risk of hip fracture (French et al., 1997). Decreasing the risk of hip fracture is a public health priority. Vegetarianwomen tended to have lower spinal bone mineral The nutritional quality of meat 89 density than non-vegetarians(Barr et al., 1998). Dunnigan and Henderson (1997)suggested that theremay be a ‘magic factor’ in meat protecting against rickets and osteomalacia. To suggest that meatplays a role in bonehealth is relatively new andexciting andwarrants further investigation. Anotheremergingbenefit for meatis selenium.Up to the middle part of the last century the main sourceof selenium in the diet wasfrom wheat-containing products. Wheat, which wasimportedmainly from the United States,washigh in selenium. Nowadays, there is a much greaterreliance on European wheat, which is much lower in selenium.This hasresultedin thefact thatour intakeof seleniumhasdecreasedsteadily duringthepastfifty years,but theproportion of selenium we get from meat has increased.Recent studieshave found that seleniummayreducetherisk of heartdiseaseandcertain typesof cancersuchas prostate andenhance the body’s ability to fight infections. Meat providesa wide range of valuablenutrients,for example, onestudy hasshownthatyoungwomenconsuming ahighmeat diet havegreaterintakes of thiamine, niacin, zinc and iron than those consuming a low meat diet (Ortegaet al., 1998). In a review on optimal iron intakes, iron containedin animal foodsis far better assimilated than in vegetarian foods(Cook, 1999). Meat is one of the richest natural sources of glutathione, an important reducing agent providing a major cellular defence against a variety of toxicological andpathological processes. Moderatelevels of glutathione are found in fruit and vegetables and low levels are present in dairy and cereal products. Glutathione inhibits formation of mutagens in model systems (TrompetaandO’Brien, 1998). It also maintainsascorbatein a reducedand functional form. Glutathione importance in the defence against chronic disease provides positive potential for meat and merits further research (Bronzetti, 1994;TrompetaandO’Brien, 1998). Therehasneverbeforebeensuchawidevarietyandchoiceof foodonsale in Western societiesand in the recent past we have seenthe development of functional foods. A functional food can be loosely described as a food that provides a health benefit beyond its basic nutritional content. In the United Statesbeef and lamb are now described as functional foods (ADA, 1999), because of the CLA they contain. At a Meat Marketing/Communication Workshop,Dr Lynne Cobiac(CSIRO) (Cobiac,2000)described somenutritive and non-nutritive meatcomponentsthat may havepotential healthpromoting properties. They aresummarisedasfollows: • Lipoic acid hasantioxidantpropertiesandhasbeenshownto bebeneficial in diabeticsandin theprevention of cataract developmentin animalmodels and cell lines. Organmeatscontainhigher quantities of lipoic acid thanmuscle meats. • Carnosine is a dipeptide composedof alanineand histidine. Carnosine is found in meatsand its antioxidant properties may confer some protection against oxidative stress. Its an anti-inflammatory agent and has anti- tumourigenic propertiesin ratsandit also playsa role in cellular homeostasis. 90 Meat processing • Biogenic amines are naturally formed from bacterial decarboxylation of amino acids or naturaldecarboxylaseactivity. They havebeenlinked with improving gut healthandcognitiveperformance. • Nucleotides are added to enteral feeds to enhance the general immune function. Organmeatsaregoodsourcesof nucleotides. • Glutathione is a tripeptide containing the sulphur amino acid cysteine. Glutathione may be the ‘meat factor’ which enhances non-haem iron absorption. • Choline is now termeda nutrient. In the United States, it is an essential nutrient andtheestimatedadequateintakeis 550mg/day for menand425mg/ day for women.Cholineis a precursor of theneurotransmitter acetlycholine, it is necessary for central nervoussystemdevelopment,folate/homocysteine metabolism, it plays a role in the immune system, fat metabolismand improves athletic performance.Beef and in particular liver is one of the richestsourcesof choline. • Carnitine is composedof lysine and methionine. Seventy-five percentof carnitine comes from the diet, mainly from red meat, lamb being a particularly good source.Carnitine carriesthe long chain fatty acidsto the mitochondria for oxidation to give energyand thuscanbe usedto improve athletic performance. It alsohasantioxidantcapabilitie sandit maybecritical for normal brain development by providing acetyl groups to synthesise acetylcholine, a neurotransmitter. This rangeof meat componentsmay have the ability to fight againstcertain cancers,CHD, anaemia andcataracts,enhance immunity andcognition,improve gut andbonehealth,regulate body weight andmay be usedin sports nutrition. However, a lot of theevidenceindicating beneficial effectsof thesecomponents comesfrom animalor cell culturemodels. Researchwill haveto beconductedin humansto demonstratetheir effect on humanhealth.But evenglancingat the amount of ‘potential’ components presentin meat indicates a positive and competitive future for meat. However, when looking to the future we must also try to visualise what changes arelikely to occurthatmayinfluencemeat consumption. Traditionally, food purchase was mainly influenced by price and sustenance. Current and future food choicedependson thesevaluesbut alongsideother factors suchas health, food safety,convenienceand welfare concerns. Changesin our social patterns,suchasmovingaway from the formal family meateatingpatterns to a ‘grazing’ or ‘snacking’ habit will becomemuchmore apparent. Increasing loss of culinary skills is alreadyevidentandis likely to rise.Themarketwill demand more convenienceand processedmeatproducts in place of traditional cuts of meats. Eating outsidethe homewill placea greater emphasis on the catering sectorasfoodproviders.Availability of ‘exotic’ meatswill escalate.Demand for organic meat is expected to rise. Competition from other foods will intensify. The emergenceof more functional foods is likely to occur. Thesearesome of the factors that will sculpture the future demandfor meatand meat products. The nutritional quality of meat 91 Meatmustadaptto thechangingenvironment.However,theemphasisbetween food choiceand healthwas neveras greatand is likely to becomeevenmore important. In the past,meatrespondedto consumer demandsby decreasingits fat content. Meat is a versatile food, however, it is time to banish the misinformation thatsurroundsthenutritional valueof meat.Meat is a

relatively low fat nutrientdensefood. Meat andmeatproducts arean integral part of the UK diet and for those who chooseto consume meat, it makesa valuable contribution to nutritional intakes(BNF, 1999). 4.9 Conclusion Therehasbeenconsiderableemotive andpublic healthdebate over the last two decades on the relative importanceof meat in the diet of modernman. Early dismissive arguments have more recently beenrevisited and challengedas a result of the continual progressand review of nutritional science. The early focus on fat as the route causeof Western-style diseases of affluence led, naively, to meat being blamed for diet-related problems.More recently, the focuson thedietsof ourancestorshaseffectively reversed this thinkingandlean red meat has beenrediscovered as a mainstay of humandiet evolution. The serious health concerns resulting from the epidemic rise in CHD, obesity, diabetesandcancers requiremorecarefully guidedpublic healthadvice,based on an holistic approachto diet andlifestyle. Lean meat can be seen as the ultimate natural functional food. Eaten in moderatequantitiesaspartof amealalongwith sufficientplantfoods,it providesa valuable,arguably essential nutrient-densesupplementto the diet with beneficial effectsfor health,both in the short andlong term.As a key ingredient of modern processedpre-prepared meals, meat, when addedas a quality ingredient, can enhance the nutritional benefits of the food product and make a significant, positive contribution to our health.It would be naı ve to ignore this potential. 4.10 References ADA REPORT(1999).Position of TheAmerican DieteticAssociation:Functional Foods.Journal of TheAmerican Dietetic Association, 99: 1278–1285. AGGETT PJ and COMERFORD JG (1995). Zinc and Human Health. Nutrition Reviews, 53: S16–S22. ALLEN, L (1997). 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A Report to The Ministry of Agriculture Fisheriesand Food. April. MAFF. London. ULBRICHT TLV and SOUTHGATE DAT (1991) Coronary Heart Disease: Seven Dietary Factors.Lancet, 338: 985–992. VAN DE VIJVER LPL, KARDINAAL AFM, COUET C, ARO A, KAFATOS A, STEINGRIMSDOITTIR L, AMORIM CRUZ JA, MOREIRAS O, BECKER W, VAN AMELSVOORT JMM, VIDAL-JESSEL S, SALMINEN I, MOSCHANDREAS J, SIGFUSSON N, MARTINS I, CARBAJAL A, YTTERFORS A and VAN POPPELG (2000).Association between transfatty acidintakeandcardiovascular risk factorsin Europe:the TRANSFAIR study. European Journal of Clinical Nutrition, 54: 126–135. WALKER ARP (1998). TheRemedying Of Iron Deficiency:WhatPriority Should It Have?British Journal of Nutrition, 79: 227–235. WATTS G, AHMED W, QUINEY J, HOULSTON R, JACKSON P, ILES C and LEWIS B (1988). Effective Lipid Lowering Diets Including Lean Meat. British Medical Journal (Clin ResEd), 296: (6617)235–237. WEST DB, DELANY JP, CAMET PM, BLOHM F, TRUETT AA and SCIMECA J (1998). 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ZHENG JJ,MASON JB, ROSENBERGIH andWOOD RJ (1993).Measurementof zinc bioavailability from beefanda ready-to-eathigh-fiber breakfast cereal in humans:applicationof awhole-gutlavagetechnique.American Journal of Clinical Nutrition, 58: 902–907. 104 Meat processing 5.1 Introduction Flavor is an important quality attribute of muscle foods and comprises mainly the two sensations of taste and aroma or smell. Although both of these factors affect the overall acceptability of foods, the aroma or flavor volatiles are of utmost importance because they influence the judgement of the consumer even before the food is eaten. While muscle

foods, namely red meat, poultry and, to a lesser extent, seafoods in the fresh, raw state have little flavor of their own, upon heat processing their specific meaty aroma develops (Shahidi, 1989; Farmer, 1992). Nonetheless, it should be recognized that the fishy aroma of raw, stored seafoods may arise from the presence of amines, derived from trimethylamine oxide which is present in gadoid fish species as an osmoregulator, or via lipoxygenase-assisted oxidation and generation of aldehydes and alcohols, especially 2,4,7-dicatrienals and cis-4-heptenal (Josephson, 1991; Lindsay, 1994). Upon heat processing, meat constituents undergo a series of thermally induced reactions to afford a large number of volatile compounds that contribute to its aroma. Some of the non-volatile precursors of volatile flavor compounds are also known to contribute to the taste of cooked meat. The most important taste-active components of meats are amino acids, peptides, organic acids, nucleotides and other flavor enhancers, among others (Shahidi, 1989). It has further been concluded that high-molecular-weight fibrillar and sarcoplasmic proteins have little effect on the development of meat flavor volatiles. Since the free amino acids and carbohydrates in meat from different species are similar, their flavor upon heat processing is also expected to be similar. However, the lipid components of meat, mainly the intramuscular lipids, are known to modify the flavor quality of thermally-processed muscle foods. Both desirable and undesirable aromas are 5 Lipid-derived flavors in meat products F. Shahidi, Memorial University of Newfoundland, St John’s formed.Of course,the speciesof musclefood being examined,methodof heat processingemployed,dietaryregimeandsexof theslaughteredanimal,aswell as freshnessof the product and storageconditions affect the flavor quality of products(e.g.LadikosandLougovois,1990;Buckley et al., 1996). More than 1000 chemicals have so far been identified in the volatiles of different muscle foods (Shahidi et al., 1985).While many of thesehavelittle influenceon flavor of meat,no single compound hasbeenidentified as being primarily responsible for thearomaof cookedmuscle foods.Thearoma-impact compoundshavebeenfound to comprisea myriad of compoundsbelonging to differentclassesof heterocyclic andacyclic compoundscontaining N, O andS atoms.In addition, lipid breakdown productshavebeenfound to participate in the development of meaty aromaas well as meat flavor deterioration. Some aspects of aromaof musclefoods, bothdesirable andundesirable arediscussed. 5.2 The role of lipids in generation of meaty flavors The role of lipids in meat flavor generationhasbeenthe subjectof extensive studies. It has beensuggested that the basic meaty aromaof beef, pork and mutton is thesameandis derivedfrom thewater-solublefraction of themuscle which is a reservoirof low-molecularweightcompounds(HornsteinandCrowe, 1960; 1963). Meanwhile, species-specific flavors in meatsoriginate from the involvement of their li pid components in Maill ard reaction during heat processing.Lipids may contribute both to desirable and undesirable flavors of meat from different species. Their effect on generation of desirable aromasin cookedmeatsmay arise from mild thermal oxidative changes which produce important flavor compounds; they may also react with componentsof lean tissues to afford other flavor compoundsand may act as a carrier for aroma compounds,thusaffecting their sensible thresholdvalues. The effect of both triacylglycerols (TAG) and phospholipids (PL) on the development of meaty aroma in meat and model systemshas been studied (Mottram, 1983,1991; Mottram and Edwards, 1983). In thesestudies,a meat sample washeatprocessed assuchor wasextractedwith hexaneor methanol- chloroform prior to cooking. While there was little difference in the developmentof meaty aromain the untreated and hexane-extracted samples, meat extractedwith methanol-chloroform hadlittle meaty aroma,but possessed a sharp roast and biscuit-like odor. In particular, the concentration of dimethylpyrazinein the headspacevolatiles wassignificantly increased with a concurrent decreasein the content of lipid oxidation products. Thus, it was concludedthat phospholipids present in the intramuscular lipids of meat were primarily responsiblefor the developmentof meaty aromas. Basedon theseexperiments,othermodelsystemsweredevisedin order to unraveltherole of phospholipidsin theformationof Maillard reactionproducts (MRP) (Farmer and Mottram, 1990). Cysteineand ribose, with or without phospholipids,wereusedto assesstheinvolvementof lipids in theformationof 106 Meat processing aroma compounds via Maillard reaction following heating in buffered solutions. Therewas a markedreductionin the amountof thiols when phospholipids, andto a lesserextent triacylglycerols,werepresent (Table5.1).Thecompounds that were formed only in the presenceof lipids were 2-pentylpyridine, 2alkylthiophenes,alkenylthiophenes,pentylthiapyranandalkanethiols(Table5.1). Furthermore,the impactof PL wasmuch greaterthan that of TAG in affecting the flavor of systemsunderinvestigation. Formationof 2-alkylheterocyleswas generallydueto thereactionof 2,4-decadienal with ammoniaor hydrogensulfide formed from cysteine or other precursors(Fig. 5.1). Direct reactionof hexanal with amino acidswould alsoleadto theformationof 2- hexylpyridine.Formation of other alkyl substituted heterocycliccompoundsfrom participationof lipid- derivedaldehydesis alsocontemplated.Reactionof 2,4decadienaldirectly with amino acids has also beenreported.The compound2,4-dacadienal is a major breakdownproductof the omega-6fatty acids. Furthermore, 1-heptanethioland 1-octanethiolwerepresentonly in thesystemscontainingphospholipidsandtheir formation is presumedto be due to the interactionof alcoholswith hydrogen sulfide. Furthermore,MRPs may also interact with meat lipids by acting as antioxidantsin order to stabilize them.Bailey (1988),and Bailey et al. (1997) have demonstratedthat MRPs act as important antioxidants in meat model systems.It has also been shown that furanthiols and thiophenethiolsexert antioxidative activity in lipids (Eiserich and Shibamoto,1994), as well as in aqueoussolutions as evidenced by their tyrosyl radical scavenging effect (Eiserichet al., 1995).The antioxidantactivity of thesecompoundswas similar to that of ascorbicacid. Figures5.1 and 5.2 showexamplesof involvement of lipids in Maillard reactionandformationof volatile flavor compounds. Other potentially desirable flavor components that might be formed in processed meatsarefree fatty acidsandrelatedcompoundswhich areprevalent in dry-cured-ham. These compounds are formed in such products via Table 5.1 Relativeconcentrationof selectedacyclicandheterocyclicvolatilesfrom the reaction of cysteine and ribose in the absenceor presenceof beef triacylglycerols (BTAG) andbeefphospholipids(BPL) Compound No lipid BTAG BPL 3-Pentanone,2-mercapto 1 0.72 0.49 2-Pentanone,3-mercapto 1 0.77 0.47 2Furylmethanethiol 1 0.67 0.63 3-Furanethiol,2-methyl 1 0.40 0.15 2-Thiophenethiol 1 0.32 0.03 3-Thiophenethiol,2-methyl 1 0.08 0.01 Pyridine,2-pentyl 0 0.09 1 Thiophene,2-pentyl 0 0.00 1 Thiophene,2-hexyl 0 0.15 1 2-H-Thiapyran,2-pentyl 0 0.10 1 Lipid-derived flavors in meatproducts 107 fermentation reactions.The flavor characteristics of dry-cured hamhasrecently beenreported(Toldra et al., 1997). 5.3 Lipid autoxidation and meat flavor deterioration Theprimarymechanismfor thedegradation of desirable flavor in storedmeatsis lipid autoxidation. Lipids in muscle foods, particularly their phospholipid Fig. 5.1 Productionof long-chainalkyl heterocyclesfrom thereactionof 2,4-decadienal with ammoniaandhydrogensulfide. Fig. 5.2 Involvementof hexanel,anoxidationproductof linoleic acid,in productionof a trisulfide heterocycliccompound. 108 Meat processing components, undergo degradation to produce a large number of volatile compounds.While hydroperoxides, the primary products of lipid oxidation, are odorlessand tasteless, their degradation leads to the formation of an array of secondary products suchas aldehydes,hydrocarbons, alcohols, ketones,acids, esters, furans, lactones andepoxycompoundsaswell aspolymers. Theselatter classesof compoundsareflavor-active, particularly aldehydes, andpossesslow threshold valuesin thepartspermilli onor evenpartsperbillion levels, thusthey areresponsiblefor thedevelopmentof warmed-overflavor (WOF),ascoinedby Tims andWatts(1958),andmeat flavor deterioration (MFD) (e.g.Drumm and Spanier,1991).Table5.2summarizesthethreshold valuesof selectedclassesof volatile compounds. In addition, lipid oxidation products lead to the loss of nutritional value and safety,color, texture and other functional properties and wholesomenessof foods. The degree of unsaturationof the acyl constituents of meatlipids primarily dictates the rate at which MFD proceeds;unsaturated lipids being more susceptible. Autoxidation of meat l ipids gives rise to a number of hydroperoxides which, in conjunction with the many different pathways possible, decompose to a largenumber of volatile compounds.However, other factors might alsoaffect the oxidationof meat lipids andformation of WOF as well asshelf-life of products(Spanier et al., 1988;Gray et al., 1996).In chicken meat, lack of -tocopherol is the main reason for MFD and formation of undesirable WOF in products. However, cookedturkey meat, despiteits higher contentof unsaturated lipids, maynot readilydevelopWOF becauseit contains endogenous-tocopherol. In addition,presenceof heme compoundsandmetal ionsmayalsohastentheoxidationof meatli pids.Furthermore,presenceof salt and other ingredients used in cooking, such as onion, may also affect progression of MFD. It has been reported that aldehydes, generated from oxidation of lipids, reactwith thiols, a classof compoundsin onion, suchas propenethiol to produce 1,1-bis (propylthio)-hexaneand 1,2-bis (propylthio)- Table 5.2 Flavor thresholdsof somelipid oxidationproducts.1 Compound Threshold,ppm Hydrocarbons,saturated 90–2150 Alkenes 0.02–9 Furans 1–27 Alcohols, saturated 0.3–2.5 Alcohols, unsaturated 0.001–3 Aldehydes,saturated 0.014–1 Aldehydes,monounsaturated 0.04–2.5 Aldehydes,diunsaturated 0.002–0.6 Ketones,methyl 0.16–5.5 Ketones,vinyl 0.0002–0.007 1 Adaptedfrom Drumm andSpanier(1991). Lipid-derived flavors in meatproducts 109 hexane. Thesecompoundswill definitely modify flavor profile of musclefoods (Ho et al., 1994). Formation of volatile aldehydesand other lipid degradation products resultsin themasking of desirablemeatyaromaof products. Thus,the roleof bothendogenousandexogenousfactorson theoxidativestatusof muscle foodsrequiresattention (seethe following). 5.4 The effect of ingredients on the flavor quality of meat In addition to the effects of low-molecular-weight water-soluble components and lipid constituentson quality attributesof meat,other factorsmust also be carefully considered. Thus, endogenous components of meat as well as ingredientsaddedto it prior to heatprocessingareof major importance in the developmentof flavor andits quality characteristics.An attemptwill be madeto provide a cursoryaccount of these factors. 5.4.1 Lipid classesand fatty acid composition While adiposetissuesgenerallycontainover 98%triacylglycerols,phospholipids constituteamajorportionof intramuscularlipids of musclefoods.Theunsaturated fatty acids presentin TAGs of red meat and

poultry contain mainly oleic and linoleic acids,however,phospholipidscontaina relatively higher proportionof linolenicandarachidonicacids.In seafoods,longchainomega-3fatty acidssuchas eicosapentaenoicanddocosahexaenoicacidsareprevalent.Existingdifferencesin thefatty acidconstituentsof phospholipidsandtriacylglycerolsof musclefoodsare primarily responsiblefor speciesdifferentiation in cookedsamplesof meat,as discussed earlier. Furthermore, depending on the type and proportion of unsaturatedfatty acidsin musclefoods,lipid autoxidationandflavor deterioration mayproceedatdifferentrates.In thisrespect,seafoodsdeterioratemuchfasterthan chickenwhich is oxidizedquickerthanred meats. 5.4.2 Effect of transition metal ions Transition metalssuchasiron, copperandcobaltmaycatalyzetheinitiation and enhance thepropagationstepsinvolved in lipid autoxidation.For example, Fe2+ will reductively cleavehydroperoxidesto highly reactive alkoxy radicalswhich in turn abstracta hydrogen atomfrom other lipid molecules to form new lipid radicals. This reaction is known ashydroperoxide-dependent lipid peroxidation (Svingenet al., 1979). Morrisseyand Tichivangana(1985) and Tichivangana andMorrissey(1985)havereportedthat ferrousion at 1– 10ppmlevelsactsasa strongprooxidant in cookedfish muscles.Similarly, copper(II ) andcobalt (II) were effective prooxidants. These observationsare in agreement with the findings of Igene et al. (1979) who reported that iron ions were the major catalysts responsible for enhancement of autoxidation in muscle foods. Furthermore, Shahidi andHong (1991)demonstrated that the prooxidant effect 110 Meat processing of metalionswasmorepronouncedat their lower oxidationstateandfoundthat in thepresenceof chelatorssuchasdisodium saltof ethylenediaminentetraacetic acid (Na2EDTA) andsodiumtripolyphosphate (STPP),the prooxidanteffect of metal ions was circumvented (Table 5.3). Furthermore, Cassens et al. (1979) haveshownthat1–3%of thetotal amountof nitrite addedto meat duringcuring wasrecovered in the lipid extractsusing the Folch method(Folch et al., 1957). Thus, stabilization of meat lipids by nitrite may also be influenced by direct coupling of nitric oxide with lipid radicals,but most of the nitrite was in the proteinbound form as nitrosothiol, nitrite/nitrate and nitrosylheme complex, amongothers(e.g.Kanneret al., 1984). Hemoproteins in meatsare generally known for their prooxidant activity (Robinson,1924;YounathanandWatts, 1959;Pearsonet al., 1977,Igeneet al., 1979;Rhee, 1988; Shahidi et al., 1988;Johnset al., 1989;Shahidi andHong, 1991;WettasingheandShahidi, 1997);some havealsobeenreported to possess antioxidantproperties(BenAziz et al., 1971;Kanneret al., 1984;Shahidi et al., 1987;Shahidi,1989;Shahidi andHong, 1991;WettasingheandShahidi,1997). The prooxidant activity of hemecompounds arises, at leastin part, from their decomposition upon cooking of meat and liberation of free iron. Meanwhile, nitric oxide derivatives of heme pigments,namely nitrosyl myoglobin and nitrosyl ferrohemochrome (or cookedcuredmeatpigment,CCMP),arereported to haveantioxidant effect (e.g. Wettasingheand Shahidi,1997). This topic is further discussed underthe effect of nitrite andnitrite alternatives. 5.4.3 Effect of salt Sodiumchloride, or tablesalt, is an importantingredientin themeatindustry. It actsgenerally asaprooxidant, but sometimesalsoasanantioxidant(Kannerand Kinsella, 1983). In comminuted meat samples,under different processing conditions, sodium chloride did not act as an antioxidant, but its neutral or prooxidant effects were clearly demonstrated (St. Angelo et al., 1992; Wettasingheand Shahidi, 1996). Takiguchi (1989) and Kanner et al. (1991) Table 5.3 Effect of chelatorson TBA numbersof groundpork catalyzedby iron ions andHemecompounds1 Treatment NO chelator Na2 EDTA, 500 ppm STPP,3000ppm Control 3.03 0.07 0.22 Fe2+ 4.80 0.09 0.27 Fe3+ 4.60 0.08 0.37 Mb 4.20 0.07 0.38 Hb 4.33 0.10 0.30 Hm 4.35 0.07 0.33 CCMP 0.42 0.30 0.30 1 From ShahidiandHong (1991). Lipid-derived flavors in meatproducts 111 have demonstratedthe prooxidant effect of NaCl in a comminuted muscle systemandsuggested that it maypromote thedisplacementof iron from binding sitesof heme compoundsby interfering with iron-proteininteractions.The free iron ionssoformedmaycatalyzelipid peroxidation. Recently, Wettasingheand Shahidi (1996) reported that LiCl, KCl, CsCl, MgCl2 and CaCl2 exhibited prooxidant activities in a cooked meat model system (Fig. 5.3). Thus, the overriding prooxidant activity wasthought to bedueto thechloride ion of salts. The resultsof Rheeet al. (1983a,b)andCho andRhee(1995)for the effect of NaCl, KCl and MgCl2 in ground pork samples are in agreementwith our findings.Further studieson the effect of replacing chloride with their fluoride and iodide counterparts showed inhibition of lipid oxidation of meats,but bromide saltsbehavedvery similarly to their chloride counterparts (Fig. 5.4). However, the situation wassomewhat different when alkali earthhalideswere used. Thus, it was concludedthat pro- or antioxidative effects of salts are primarily dictated by their anions, but mediated by their cationsbecause of existing differences in their ability to participatein iron-pairing interactionswith the anion counterparts. Fig. 5.3 Effect of chloridesaltson oxidationof meatlipids, asreflectedin 2thiobarbituricacidreactivesubstances(TBARS) values,overa seven-daystorageperiod. 112 Meat processing 5.4.4 Effect of nitrit e and nitrit e alternatives Nitrite is a key ingredient of the cure and is responsible for producing the characteristicpink color in cooked-curedproducts andcontributesto thetypical flavor associatedwith curedmeats andpreventsthe formation of warmed-over flavor aswell asrenderingmicrobial stability to products (Fox,1966;Haddenet al., 1975; Pearsonet al., 1977; Shahidi, 1992). The relationship of nitrite to curedmeat flavor was first describedby Brooks et al. (1940). Theseauthors presumed thatanadequate curedflavor couldbeobtained with a relatively low, 10 mg/kg, concentrationof nitrite, but Simonet al. (1973)andMacDougall et al. (1975)showedhigher tastepanelscoreswhen theaddition level of nitrite was increased. The role of nitrite in modifying flavor of cookedmeat(Haddenet al., 1975; MacDonald et al. 1980) and suppressinglipid oxidation and MFD in cooked meats(Fox,1966;Pearsonet al., 1977;Fooladi et al., 1979)is well documented. Sato and Hegarty (1971) reported that nitrite at 50 ppm was capable of suppressing oxidation of meat lipids. However, Shahidi et al. (1987) demonstrated that presenceof a reductant such as sodium ascorbate was Fig. 5.4 Effect of sodiumhalideson oxidationof meatlipids, asreflectedin 2- thiobarbituricacid reactivesubstance(TBARS) valuesandmeasuredasmalonaldehyde (MA) equivalents/kgsample,over a seven-daystorageperiod. Lipid-derived flavors in meatproducts 113 essential to eliminatelipid oxidationin meatswhenlessthan150ppmof nitrite wasused.Meat flavor deterioration, thereforedoesnot developin cured meat. This observation might be attributed to any or a combination of the effects related to (a) stabilization of heme pigments (Zipser et al., 1964), (b) stabilization of membranelipids (Zubillaga et al., 1984), (c) chelation of free metalionsandprooxidantcatalysts(ShahidiandHong,1991),and(d) formation of nitrosylheme derivatives possessing antioxidant effects (Morrissey and Tichivangana,1985;KannerandJuven,1980;Shahidi et al., 1988; Shahidi and Hong, 1991). Hemeproteinsandtheir relatedproducts aswell astransitionmetalionshave been implicated in meat lipid oxidation (e.g. Shahidi and Hong, 1991), as discussedearlier. As a resultof heatprocessing,hemecompoundsin untreated meats arerapidly oxidizedandproduceferrousandferric ions. In cured meats nitric oxide, producedfrom nitrite, reactswith myoglobin and also combines with Fe2+ ions and thus suppressesMFD (see Table 5.3). The chelating properties of nitrite may be duplicated by the action of sequesterantssuchas Na2EDTA andSTPP.The antioxidantactivity of some nitrosylhemecompounds hasbeendemonstratedby Ben Aziz et al. (1971)andWettasingheandShahidi (1997). The exact mechanism by which this antioxidative effect is exerted remainselusive. Nonetheless,stabilization of iron in theprotohemecompounds may be, at leastin part, responsible. Shahidi et al. (1987)andWettasingheandShahidi(1997)haveclearlyshown that the preformedcookedcured-meatpigment (CCMP) (Fig. 5.5) acts as an antioxidant in a meat andin a -carotene-linoleatemodelsystem,respectively. However, CCMP in the presenceof ascorbatesmay form potent antioxidant combinations with evidence of strong synergism between the components (Shahidi, 1992).Furthermore, this synergistic effect wasnoted for bothnitrosyl myoglobin and CCMP in which iron atomsare in the ferrous form and their coordination sitesareoccupied.Suggestionshavebeenmadethatnitrosatediron porphyrin compoundsact in the early stagesof the reaction to neutralize substrate free radicals and thus inhibit oxidation of meatlipids (Kanneret al., 1984). During the curing process,S-nitrosocysteine (RSNO) may also be formed. This compoundactsasa strongantioxidantas it hasbeenreported to inhibit oxidation of turkey meat (Kanner and Juven,1980). Effectiveness of nitrite in inhibition of MFD through other mechanisms has been further demonstratedin the literature(Ohshimaet al., 1988). Inhibition of oxidationof unsaturated fatty acidsandformation of secondary carbonyl compounds as well as other degradation products of l ipid hydroperoxidesin cured products results in a drastic reduction in the number andconcentrationof volatiles in thecured meat products ascomparedwith their uncured counterparts (e.g. seeTable 5.4 ). In particular, formation of higher aldehydesis effectively suppressed(Cross and Ziegler, 1965; Shahidi,1992). CrossandZiegler (1965)havealsoreported thatpassageof volatiles of uncured beef and chicken through an acidic solution of 2,4-dinitrophenylhydrazine, which stripped their carbonyl compounds,resultedin the revelation of a flavor 114 Meat processing which wasindistinguishable from that of cured ham.However, curing of sheep meatdid not removethespecific‘sheepmeat’ odorof theproduct (Younget al., 1994).This effect is thoughtto bedueto thepresenceof 4-methylnonanoicand, to a lesserextent, 4-methyloctanoic acids in cooked samples of meat from mutton. Therefore, it appears that the basic flavor of cookeduncuredmeats without havingbeenaffectedmuchby their lipid components is in mostcases similar to their cured counterparts,but becomesmaskedwith carbonyl products, formedvia autoxidation.Lindsay (1997)hasalso thoughtthatnitrophenolsmay haveaninfluenceon thecharacteristicaromaof curedmeatproducts. However, this suggestion hasnot yet beensupported by relevant experimental results. Based on these findings, we have proposed that any other agent or combinations that could prevent lipid oxidation would, in principle and in general, duplicatetheantioxidantrole of nitrite in thecuringprocessfor species other than mutton, thus preventing MFD (Shahidi, 1991). To verify this simplistic view, we examined the effect of commonly usedfood antioxidants andchelatorsaswell asother curingadjunctssuchassalt,asdiscussed earlier,as Fig. 5.5 The chemicalstructureof cookedcured-meatpigment(CCMP). Table 5.4 Effect of curing on the relative concentrationof major aldehydesin pork flavor volatiles Relativeconcentration Aldehyde

5.4 Effect of curing on the relative concentrationof major aldehydesin pork flavor volatiles Relativeconcentration Aldehyde Uncured Cured Hexanal 100 7.0 Pentanal 31.3 0.5 Heptanal 3.8 well asascorbatesandpolyphosphates in preventionof MFD andformation of off flavors(ShahidiandPegg,1992).Surprisingly, curingadjunctshadamarked effect in controlling MFD asin curedmeats. Furthermore, additionof CCMPto themixture, with or without anauxiliary antioxidantsuchasTBHQ, resultedin anear-duplicationof theaction of nitrite in preventing lipid oxidationin cooked, storedmeats(Table5.5). Having recognizedthe importanceof curingadjuncts on the flavor of meats, we developed nitrite-free curing systems in which ascorbates,polyphosphates, CCMP and possibly an antimicrobial agent,with or without any additional agents were usedto duplicateall propertiesof nitrite-curedmeats. For further informationon this topic, the readeris referredto publications by Shahidiand co-workers. 5.5 The evaluation of aroma compoundsand flavor quality Flavor quality of muscle foods may be evaluated by employing sensory techniques.Both desirable andundesirablearomacharacteristicsof products are easilyrecognized.A thoroughdiscussionof sensoryanalysisof meatproductsas well asapplicationof instrumental methodsandchemical procedures is provided in the literature. While many indicators may be usedfor suchevolutions,it is most appropriate to select the ones that show maximum variation under experimental conditions of heat processing, packaging and storage. In this connection, the use of the 2-thiobarbituric acid reactive substances(TBARS) test is commonplace.Althoughtherearemany shortcomingsassociatedwith this method of evaluation, nonetheless,it provides a realistic assessmentof the relative oxidative stability of products(e.g. Shahidi and Wanasundara,1996). This topic hasbeenthoroughlydiscussedin theliterature. Furthermore,hexanal, a prominantoxidationproduct of linoleic andother omega-6fatty acids maybe Table 5.5 Inhibition of formationof selectedvolatile oxidationproducts(%) in nitrite- andnitrite-freecuredmeats Additive(s) TBARS Hexanal 2-pentyl- Nonanal 2,4-deca- furan dienal SA 48 50 80 21 63 STPP 70 62 40 34 57 SA+STPP 92 88 88 61 64 SA+STPP+CCMP 99 98 97 91 90 SA+STPP+CCMP 99 99 98 92 96 +TBHQ SA + NaNO2 98 99 98 95 95 Abbreviationsare:TBARS, 2-thiobarbituric acid reactivesubstances;SA, sodiumascorbate;STPP, sodiumtripolyphosphate; CCMP, cookedcured-meat pigment; TBHQ, tbutylhydro quinone;and NaNO2, sodiumnitrite. 116 Meat processing used effectively to evaluate the oxidative state and off flavor formation in cooked red meatsand poultry. However, when fatty acids in the food are dominated by omega-3 fatty acids, such as eicosapentaenoic and docasa- hexaenoic acids,useof hexanalasan indicatormight not be appropriate. Thus, propanal may be usedasan indicator for evaluation of aromadeterioration of seafoodsandmarine oils. 5.6 Summary The formation of desirablearomasin musclefoods has beenfound to arise, primarily, from thereactionof low-molecular-weight,water-soluble compounds andinvolvementof lipids in Maillard reaction.While lipids andtheir breakdown products contribute positively to the flavor quality of freshly preparedmuscle foods, their further oxidationis recognized to causeMFD. Breakdown products of lipids suchasaldehydes, ketonesandrelated compoundshavelow threshold valuesand,evenat relatively low concentration,maymaskthedesirable aroma of heterocyclic andacyclic heteroatomic compounds.Thus,controlof oxidation in muscle foods is necessary in order to protect them against generation of undesirablearomasandflavor deterioration.Furthermore it is desirable to devise formulations which could accentuate the desirablemeaty aroma in products which remaineffectiveduring prolongedstorage. 5.7 References BAILEY, M.E. 1988.Inhibition of warmed-over flavor with emphasison Maillard reactionproducts. Food Technol. 42(6): 123–132. BAILEY, M.E., CLARKE, A.D., KIM, Y.S. and FERNANDO, L. 1997. Antioxidant properties of Maillard reaction products as meat flavor compounds. In Natural Antioxidants: Chemistry, Health Effects and Application. Edited by F. Shahidi, AOCS Press, Champaign,pp. 296–310. BEN-AZIZ, A., GROSSMAN, S., ASCARELLI, I. and BUDOWSKI, P. 1971. Linoleate oxiation induced by lipoxygenaseand heme proteins: a direct spectro photometric assay.Anal. Biochem.34: 88–100. BROOKS,J., HAINER, R.B., MORAN, T. and PACE, J. 1940. The function of nitrate, nitrite and bacteria in the curing of bacon and hams. Department of Scientific and Industrial Research,Food Investigation Board. Special Report49. His Majesty’s StationeryOffice, London.pp. 2–4. BUCKLEY, D.J.,MORRISSEY, P.A. andGRAY, J.I. 1996.Influence of dietary vitamin E on theoxidativestability andquality of pigment. J. Anim.Sci.73: 3122– 3130. CASSENS, R.G., GREASER,M.L., ITO, T. and LEE, M. 1979. Reactionsof nitrite in meat.Food Technol. 33(7): 46–57. CHO,S.H.andRHEE,K.S. 1995.CalciumchlorideeffectsonTBA valuesof cooked Lipid-derived flavors in meatproducts 117 meat.J. Food Lipids 2: 135–143. CROSS,C.K. and ZIEGLER, P. 1965.A comparisonof the volatile fractionsfrom cured anduncuredmeat.J. Food Sci. 30: 610–614. DRUMM, T.D. and SPANIER, A.M. 1991. Changes in the content of li pid autoxidation and sulfur-containing compoundsin cooked beef during storage. J. Agric. Food Chem.39: 336–343. EISERICH,J.P.andSHIBAMOTO,T. 1994.Antioxidantactivity andMaillard-derived sulfur-containing heterocyclic compounds. J. Agric. Food Chem. 42: 1060–1063. EISERICH, J.P.,WONG, J.W. and SHIBAMOTO, T. 1995. Antioxidative activities of furan- andthiophenethiolsmeasured in lipid peroxidation systemsandby tyrosyl radical scavenging assay. J. Agric. Food Chem.43: 647–650. FARMER,L.J. 1992.Meatflavor in The Chemistryof Muscle-BasedFoods. Edited by D.E. Johnston, M.K. Knight and D.A. Ledward. Royal Society of Chemistry, London. pp. 169–182. FARMER, L.J. and MOTTRAM, D.S. 1990. Interaction of lipid in the Maillard reactionbetween cysteineandribose:theeffectof a triglyceride andthree phosphlipids on the volatile products. J. Sci. Food Agric. 53: 505–525. FOLCH, J., LEES, M. and SLOANE-STANLEY, G.H. 1957. A simple methodfor the isolation andpurification of total lipids from animaltissues.J. Biol. Chem. 226: 497–509. FOOLADI, M.H., PEARSON,A.M., COLEMAN, T.H. andMERKEL, R.A. 1979.Therole of nitrite in preventing developmentof warmedoverflavour. FoodChem.4: 283–292. FOX, J.B., JR. 1966.The chemistry of meat pigments.J. Agric. Food Chem.14: 207– 210. GRAY, J.I., GOMAA, E.A. andBUCKLEY, D.J. 1996.Oxidative quality andshelf-life of meats. Meat Sci. 41: 8111– 8123. HADDEN, J.P.,OCKERMAN,H.W., CAHILL, V.R., PARRETT, N.A. andBORTON,R.J.1975. Influenceof sodiumnitrite on thechemical andorganolepticpropertiesof comminutedpork. J. Food Sci. 40: 626–630. HO, C-T., OH, Y-C. andBAE-LEE, M. 1994.The flavour of pork. In Flavor of Meat and Meat Products. Edited by F. Shahidi, Blackie Academic and Professional,Glasgow, pp. 38–51. HORNSTEIN, I. andCROWE, P.F.1960.Flavourstudieson beefandpork. J. Agric. Food Chem.8: 494–498. HORNSTEIN, I. andCROWE, P.F. 1963.Meat Flavor: Lamb. J. Agric. 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Shahidi. Blackie Academic& Professional,Glasgow, pp. 71–97. ZIPSER,M.W., KWON, T.-W. andWATTS,B.M. 1964.Oxidative changes in cured and uncuredfrozencookedpork. J. Agric. Food Chem.12: 105–109. ZUBILLAGA, M.P., MAERKER, G. and FOGLIA, T.A. 1984. Antioxidant activity of sodiumnitrite andmeat.J. Am. Oil Chem. Soc.61: 772–776. Lipid-derived flavors in meatproducts 121 6.1 Introduction Colour stability of meat products is influenced by a large number of factors some being of biochemical nature, some due to handling during the slaughter process and some due to packaging and storage conditions. This chapter focuses on modelling the effect of the external factors applied during packaging and storage. However, meat from different sources show different tendencies to undergo colour deterioration and this variation in internal factors influences the developed models. Therefore some consideration will also be given to discussing how internal factors like, e.g., muscle type and addition of nitrite in cured meat affect the models. Modelling can be used to identify the most important factors/interaction of factors affecting quality loss and to define critical levels of these factors, thereby forming the basis for proposing the optimal packaging and storage conditions or the best compromise, if several deteriorative reactions need to be considered. Caution in choosing the optimal packaging and storage conditions can largely improve the colour shelf life of meat products. When packaging fresh meat products an elevated oxygen (O2) partial pressure needs to be maintained to keep the meat pigment myoglobin in its oxygenated bright red state. Through modelling of a MAP system for fresh beef, the most critical external factors have been identified to be storage temperature and gas composition (Jakobsen and Bertelsen, 2000). Through modelling of a MAP system for cured meat products the most critical external factors have been identified to be a low availability of oxygen combined with exclusion of light (storage temperature was kept constant at 5ºC) (Mølleret al., 2002). However, low availability of oxygen is not solely ensured by reducing the residual oxygen 6 Modelling colour stability in meat M. Jakobsen and G. Bertelsen, Royal Veterinary and Agricultural University, Frederiksberg level in the headspace during the packaging process. Other equally critical factorsareahighproduct to headspaceratio andapackaging film of low oxygen transmission rate (OTR) of the packagingfilm (Møller et al., 2002). 6.2 External factors affecting colour stability during packaging and storage Modified atmosphere packed meat is a complex and dynamic systemwhere severalfactors interact (Zhaoet al., 1994).Modelscanbeusedto describe how the initial packageatmospherechanges over time andhow these changes affect product quality and shelf-life. The dynamic changes in headspace gas composition during storagecan be modelled asa function of gastransmission ratesof the packaging material, initial gascomposition, product and package geometry, gasabsorption in the meatetc. Combinedwith the knowledge from modelson quality changes in the meatasa function of packaging andstorage conditions such as storage temperature, gas composition and light exposure, predictions of product shelf life can be made. Pfeiffer et al. (1999)developed simulations of how product shelf life changeswith different packaging and storageconditionsfor a wide rangeof food products(primarily dry products). However, at presentsufficient modelsfor many quality deteriorative reactions arelacking andonly a few attempts havebeenmadeto modelchemical quality changes in meat products, in contrastto modelling of microbial shelf-life, where extensive work hasbeenperformed(McDonald andSun, 1999). 6.3 Modelling dynamic changesin headspacecomposition 6.3.1 Permeability of the packaging film Headspace gas composition changes dynamically due to several factors. Gas exchange with the environmentoccursover the packagingfilm, if the partial pressureof a gasdiffers on the two sides of the film. The amount of gasthat permeatesover the film canbecalculated from equation 6.1 (Robertson,1993): Qˆ P p t A 6:1 Q ˆ the amount of gasthat permeatesover the film (cm3) P ˆ the permeability of the packaging film (cm3/m2/24h/atm) p ˆ the differencein gaspartial pressureon the two sidesof the film (atm) t ˆ the storagetime (24h) A ˆ the areaof the package (m2) Different gases have dif ferent permeabil ity through the same film. For conventional films, the permeability of CO2 is generally 4–6 timesgreater than that of O2 and12–18times largerthanthat of N2. The permeability of a plastic film is roughly proportional to the thicknessof the film. Doubling the film thicknessapproximately halvesthe permeability of the film. Modelling colour stability in meat 123 Permeability is also influencedby storagetemperatureandrelative humidity. Pfeiffer et al., (1999) found that the empirical equation 6.2 fitted well with literaturedatafor oxygenpermeability. P…T;RH† ˆ exp…c0‡ c1=T ‡ c2 RH ‡ c3 RH2† 6:2 P ˆ the permeability of the packaging film T ˆ storagetemperature RH ˆ storagerelativehumidity c ˆ experimentally derivedcoefficient. Gasexchangeover thepackaging film is of particularimportance whenthefilm needsto maintain a narrowly definedgasconcentrationasshownin theexample in section 6.5, where the permeability of even small amounts of O2 into a package containing a cured meat product is considered a critical packaging parameter. 6.3.2 Gas absorption in the meat Headspacegascomposition canalsochangedueto gasabsorptionin the meat. Packaging in elevatedlevelsof CO2 canresultin largeamountsof CO2 absorbed in themeat(JakobsenandBertelsen,2002;Zhaoet al., 1994)andtherebylarge changescompared to theinitial ly appliedgascomposition.Absorptionof O2 and N2 is negligible comparedto the absorptionof CO2 (Jakobsenand Bertelsen, 2002). Models for CO2 solubility as a function of packaging and storage parameterssuchasproduct to headspacevolume ratio, temperature and initial CO2 level weredevelopedby Zhaoet al., (1995)andDevlieghereet al., (1998). FavaandPiergiovanni (1992)developedmodels of CO2 solubility asa function of differentcompositionalparameters,aw, pH, protein,fat andmoisturecontent. As regardsgasabsorption, equilibrium is obtained during the first one or two days. Microbial or meat metabolism can also causeslight changes in gas compositionby usingO2 andproducing CO2. Whenit is understoodhow the gasatmospherecanchangefrom the initially applied atmosphere under different packaging and storage conditions, this knowledgecanbe usedto evaluate the effect on quality deteriorating reactions. Besidesmicrobial growth, the primary concern when packaging both freshand cured meatproductsis colour stability. The mechanismsof colour changes in freshmeatproducts andcuredmeatproducts arecompletely differentascanbe seenfrom the exampleson modelling given in the following two sections. 6.4 Modelling in practice: fresh beef Jakobsen and Bertelsen(2000) and Bro and Jakobsen (2002) modelledcolour stability of fresh beef underdifferent packaging and storageconditions. In all cases colour measurementswere performed using a Minolta Colorimeter CR- 124 Meat processing 300 (Minolta, Osaka,Japan) using the L; a; b coordinates (CIELAB colour system). Red colour was expressed as the avalue, the higher the a-value the redderthesample.Whenpackaging freshredmeatselevatedO2 partialpressures are used to stabi l ise myoglobin in its bright red oxygenated form (oxymyoglobin). However,elevatedO2 levels may increase somedeteriorative reactions,e.g.,lipid oxidation.Consequently, it is interesting to investigateif a level of O2 exists, which is acceptable when considering both colour stability and lipid oxidation. Jakobsen and Bertelsen (2000) investigated different packaging andstorageconditions(Table6.1)anddevelopeda regression model/ responsesurfacemodel predicting the colour avalue as a function of storage time, storagetemperature and O2 level basedon steaksof Longissimusdorsi muscles from four different animals.Theresulting model(equation 6.3)contains main effects of the three factors plus two-way interactions and two squared effects. Interpretationof the model is best done by exploring the response surfaceplot (Fig. 6.1). a-valueˆ 0‡ 1 Day‡ 2 Temp‡ 3 O2‡ 4 DayTemp‡ 5 DayO2‡ 6 TempO2‡ 7 Day Day‡ 8 Temp Temp 6.3

Where is

a regression coefficient. Figure6.1showsa responsesurfaceplot varyingthetwo factors,temperature and O2 level, while keeping the third factor, storagetime, constantat day 6. Figure6.1 revealsan interval of approximately 55–80%O2, wherethe O2 level doesnot affect the colour a-valuesignificantly (the nearhorizontal lines in this interval mean thatonly temperature influencesthea-value). Theborders of this interval changea little depending on thesetting of theday.But it is evident that the

O2 level can be reduced from the normally used70–80%without adverse effect on colour shelf-life. The complexity of the interactions/squaredtermsin equation 6.3 called for further searchfor adequate models. A novel approach called GEMANOVA (Generalized Multiplicative ANOVA) wastherefore usedin Bro andJakobsen (2002). In this study the effect of different packaging and storageconditions (Table6.2) on colourstability andlipid oxidation of steaksof Longissimusdorsi muscles from threedifferent animals was investigated.The effect of light was evaluatedasthetime of exposure to a fluorescenttubecommonly usedfor retail display (Philips Fluotone TLD 18W/830 yielding 1000 lux at the package surfacefor 0, 50 or 100% of thestoragetime). Evenwhen considering only two Table 6.1 Packagingandstorageconditionsusedin the modelsdevelopedin Jakobsen andBertelsen(2000) Modelling factor Abbreviation No. of levels Settingof levels Storagetime (days) Day 5 2, 4, 6, 8, 10 Temperature(ºC) Temp 3 2, 5, 8 O2 level (%) O2 5 20,35,50,65,80 Modelling colour stability in meat 125 factor interactionsa traditional ANOVA modelfor the experimentin Table6.2 would look like equation 6.4 (beforeremoval of any insignificant effects). a-valueˆ 0 ‡ 1 Day‡ 2 Temp‡ 3Light ‡ 4 O2 ‡5Day Temp‡ 6 Day Light ‡ 7 Day O2‡ 8 Temp Light ‡9 TempO2‡ 10 Light O2 6.4

Where is a regressioncoefficient. On thecontrary, whenapplying

theGEMANOVA modelthe interactionsare modelled as one higher-order multiplicative effect, resulting in equation 6.5 Fig. 6.1 Responsesurfaceplot of predicteda-values(averageof four animals)aftersix daysstorageat different temperaturesanddifferent oxygenlevels (Adaptedfrom JakobsenandBertelsen,2000). Table 6.2 Packagingandstorageconditionsusedin the modelsdevelopedin Bro and Jakobsen(2002) Modelling factor Abbreviation No. of levels Settingof levels Storagetime (days) Day 4 3, 7, 8, 10 Temperature(C) Temp 3 2, 5, 8 Light exposure(%) Light 3 0, 50, 100 O2 level (%) O2 3 40, 60, 80 126 Meat processing (before removal of any insignificant effects). The interpretation of the GEMANOVA model is much more simple than the ANOVA model as is discussed in detail in Bro (1997)andBro andJakobsen (2002). a-valueˆ Day Temp Light O2 6:5 The resulting GEMANOVA model for the datain Table 6.2 canbe written as equation 6.6, since the effect of the O2 level is insignificant in the interval between 40–80% O2 (Bro andJakobsen2002).Theinteraction termDay Temp Light cO2 describesdeviationsfrom thea-valueonday0 in avery simpleway, andinterpretationof the model parameters canbe performedfrom Fig. 6.2. a-valueˆ a-value0 ‡ Day Temp Light cO2 6.6 Wherea-value0 is the a-value at day 0 andcO2 is a constant. For all settingsof the factors the estimatedresponseis simply the starting level of thea-valueplustheproduct of thefour effectsseenfrom theordinatesin Fig. 6.2.Themultiplicative term in equation 6.6 is 0 on day0. Furthermore it is easilyseenthat: Fig. 6.2 Parameterlevelsfor the interactionterm …Day Temp Light cO2† in equation 6.6 (Adaptedfrom Bro andJakobsen,2002). Modelling colour stability in meat 127 • All changesin colour a-value are negative (colour becomesless red) comparedto the starting colour. The changeis calculated as the product of the four parametersDay, Temp, Light andO2, which consistof onenegative number (Day) andthreepositive numbers. • The changes are relative and the effect of the individual factors can be interpretedindividually. For example whengoing from 2ºCto 8ºCtheTemp loading increasesfrom 1.2 to 2.4,meaningthat regardlessof all otherfactors the decreasein a-valueat 8ºC is twice the decreaseat 2ºC. • The effectsof storagetime andtemperaturearemost important. • Theeffectof light is minor, althoughan increase in time of exposure to light seemsto result in a decreasedcolour a-value. • Theeffectof theO2 level is insignificant in the interval from 40–80%andis therefore containedin equation6.6 asa constant. The GEMANOVA model confirms the results from Jakobsen and Bertelsen (2000)by emphasisingtheimportanceof keepinga low storagetemperatureand showing no effect of O2 level in the interval between approximately 40–80%. However, the interpretationof the model is much more simple, since the effect of eachfactor canbe interpretedindividually. Likewise applying the GEMANOVA model on the data set in Table 6.1 results in equation 6.7which is muchmoresimple to interpretthanequation 6.3. a-valueˆ a-value0‡DayTempO2 6.7 Where a-value0 is the a-valueat day 0. From Fig. 6.3 the effect of the individual factors canbe interpreted,andthe stable interval between 40–80%O2 is evident. It is rathersurprisingthat 40% O2 is sufficient to ensurethe stability of the bright red meat colour, as an O2 level of 70–80% is commonly usedin the industry. The applied product to headspacevolumeratio for the experiments in Tables 6.1 and6.2 wasapproximately 1:9. The largeheadspacevolumemight cause only minor changes in headspace gas composition (oxygen partial pressure) to take place during storage.However, when packaging fresh meat products for retail sale, a large headspacevolume is common. Furthermore, large amounts of oxygenhaveto permeateover the film or be usedfor meat/ microbial metabolism before a noteworthy changein oxygen partial pressure takes place, and the meatcolour becomesaffected.A reductionin the applied oxygenlevel leavesthe possibility of using morecarbon dioxide or nitrogenin the package headspace. 6.5 Modelling in practice: cured ham When packagingcured meatproducts it is important to keepthe O2 and light exposure at a minimum. Møller et al. (2002)investigatedthecolourstability of cured hamunderdifferentpackagingandstorageconditionsaccording to Table 128 Meat processing 6.3.ColourmeasurementswereperformedusingaMinolta ColorimeterCR-300. The effect of light wasevaluatedas the light intensity from a fluorescent tube measuredon thepackagesurface. Theresultingregression model (after removal of insignificant effects) considering only two-factor interactions is shown in equation 6.8. Fig. 6.3 Parameterlevels for the interactionterm …Day TempO2† in equation6.7. Table 6.3 Packagingandstorageconditionsusedin themodelsdevelopedin Møller et al., (2002) Modelling factor Abbreviation No. of levels Settingof levels Storagetime (days) Time 5 1, 3, 6, 9, 14 ResidualO2 level (%) ResO2 3 0.1, 0.25,0.5 MeasuredO2 level (%) MeasO2 – Continuously OxygenTransmissionRate OTR 3 0.5, 10, 32 (ml/m2/24h/atm) Volume ratio Vol 3 1:1, 1:3, 1:5 (productto headspace) Light intensity (Lux) Light 2 500,1000 Nitrite content(ppm) Nit 2 60, 150 Modelling colour stability in meat 129 a-valueˆ 0 ‡ 1ResO2‡ 2Vol ‡ 3Light ‡ 4Nit ‡ 5Time ‡6MeasO2‡7ResO2Light‡8ResO2Time‡9ResO2MeasO2 ‡10 Vol MeasO2‡ 11 Light MeasO2‡ 12 Time MeasO2 6.8

Where is a regressioncoefficient. As expected, thea-

valuedecreaseswith increasedtime, increasedresidual O2 level, increased OTR, increased light intensity and decreasednitrite content. However, the studyalsoshows the importanceof interactionsbetween factors. Especially the interaction between O2 level and product to headspacevolume ratio is interesting.Normally, the focus is on the residual O2 level (%) in the package andit is commonly overlooked that alsothe total amountof available oxygenmoleculesis important.Thetotal amount of oxygenmoleculesavailable for colour deteriorative reactions is determined by the residual oxygen level after packaging, themeatto headspacevolumeratio, andtheamountof oxygen thatpermeatesinto thepackageheadspacein combination.It is not sufficient to keepa low O2 level in thepackageheadspace.If theheadspacevolumeis large therewill still be plenty of oxygenmolecules for colour deterioration. Figure 6.4 shows a contour plot of the interactionbetween‘measured O2 level’ and ‘volume ratio’ (the remaining factors are fixed to the following settings: residual O2 levelˆ 0.25%, illuminanceˆ 1000 lux, nitriteˆ 60 ppm, storagetimeˆ 9 days). The a-value of the productfor a given combination of ‘measuredO2 level’ and ‘volume ratio’ canbe found from the plot by reading theavaluefrom thecorrespondingcontour line, e.g.,applying 0.10%‘measured O2 level’ anda ‘volume ratio’ of 1:1.3resultsin anavalueof 5.6after9 daysof storage. It appears that to maintain a high a-value, it is necessaryto keepboth the oxygenlevel andthe headspacevolume low (lower left cornerof the plot), solely keepingthe O2 level low is not sufficient. The interactionbetween O2 Fig. 6.4 Contourplot of the interactioneffect betweenvolumeratio (product:headspace)andmeasuredO2 level (%) after nine daysstorage(Adaptedfrom Møller et al., 2002). 130 Meat processing level and light intensity is also important. In order to maintain a goodproduct colour it is necessarysimultaneously to keep both the O2 level and the light intensity low (Møller et al., 2002). 6.6 Internal factors affecting colour stability 6.6.1 Fresh meat Largevariationsin colourstability betweenmeatof differentorigin canstrongly influencethedevelopedmodels. Different meattypes showlargevariability due to different myoglobin contentand different metabolic type (Renerre, 1990). Thecontentof myoglobinis, e.g.,largestin beeffollowedby lambandpork,and the colour of pork is more stable than the other two species. Steaks of Longissimus dorsi muscles have high colour stability and steaksof Semimembranosusmuscleshavemediumcolour stability. Animals of differentage, breed, feeding, etc., will also show differences in colour stability (Renerre, 1990;Jensen et al., 1998) It appears from Figs 6.5 and 6.6 that there is a huge variation in colour stability between meat from different sources.A range of intrinsic factors influencethe oxidative balancein raw meatandthereby the colour stability of Fig. 6.5 Measureda-valuesfor four differentanimalsstoredin 80%O2 at 8ºC(Adapted from JakobsenandBertelsen,2000). Modelling colour stability in meat 131 the meat (Bertelsenet al., 2000). Thus the oxidative stability of muscles is dependent on the composition, concentrations, and reactivity of (i) oxidation substrates(lipids, protein and pigments), (ii) oxidation catalysts (prooxidants such as transition metals and various enzymes) and (iii) antioxidants, e.g., vitamin E andvariousenzymes. For a review seeBertelsenet al. (2000). Meat from different origins show different tendencies to undergocolour deterioration. It is thereforenecessaryto investigatemeatfrom a large number of sourcesto beableto makegeneralconclusions.Despitethelargevariations in colour stability of meat from thedifferentanimalsandmuscle types investigated in section 6.4 the pronouncedeffect of temperature andthe constant interval of O2 arecommon. Only the rateof colour deterioration differs. 6.6.2 Cured meat A range of intrinsic factors affects the colour stability of nitrite cured meat products.Themostimportantarethe level of nitrite andthecontentof vitamin E Fig. 6.6 Measureda-valuesfor two muscletypesfrom threedifferentanimals,storedin 80% O2 at 8ºC. Longissismusdorsi muscles(closedsymbols)andSemi-membranosus muscles(opensymbols). 132 Meat processing (Weberetal., 1999).Thus,optimumcolourstabilitycanbeachievedonly by using a multifactorialapproach,wherebothintrinsic andextrinsicfactorsareconsidered (Bertelsenetal., 2000).FromFig. 6.7theeffectof thenitrite contenton therateof colour

deteriorationis evident.Increasingthenitrite contentstabilisesthecolour. Thisresultemphasisesthenecessityof investigatingthespecificproductof interest in orderto definecritical levelsof packagingandstoragefactors. 6.7 Validation of models The examples in sections 6.4 and 6.5 clearly demonstrate the usefulness of modelling for identification of the most importantfactors/interactionof factors affecting colour deterioration. They also demonstrate how critical limits/ intervals of these factors can be identified. For freshbeef it is recognisedthat keepinga low storagetemperatureis the key parameterto obtaina long colour Fig. 6.7 Measureda-valuesfor curedhamcontaining150 ppm (filled circles)and60 ppm (opencircles)nitrite (eachpoint is an averageof 42 samples)(Datafrom Møller et al., 2002). Modelling colour stability in meat 133 shelf-life. In addition a wide intervalof oxygenpartialpressureexiststhat result in optimal colour stability, leaving the possibility of optimising the gas composition with respectto other quality deteriorating reactions, e.g., lipid oxidation without compromisingthecolourstability. With respectto cured meat products it is importantto realisethat severalfactors influencethe total amount of O2 molecules available for oxidation. Modelling of MAP systems shows great potential for optimising/tailoring storageand packaging parameters to maintain product quality, in this casea goodmeatcolourstability (JakobsenandBertelsen,2000; Lyijynen et al., 1998; Pfeiffer et al., 1999). As shown,modelling can be usedto identify the most important factors affecting quality loss and to define critical levels of these factors. Multivariableexperimental design is necessaryto beableto investigate the large number of influencing factors on several levels as well as the interactions between factors. However, due to large biological differences between meat from different sourcesand to differences in handling and processingof themeatit is alsoimportantto recognise that internal factors have aneffecton thedevelopedmodels. Thedescribedmodelscanbeusedto predict thegeneralresponseof a meatproductto changes in external factors, but not to predict the exacta-valuefor a certainpieceof meat. That would requiremuch morespecificmodels (for eachproducttype)andincorporationof knowledgeon the internal factors into the models(JakobsenandBertelsen,2000). 6.8 Future trends The obvious tools for optimisation of productshelf life through controlling the packaging andstorageconditionsarecomputer simulations.Modelsof changes in headspace gas composition should be combined with models describing changes in the most importantquality parameters.A computerprogramshould be given inputson: • permeability of the different packagingfilms to be compared • storagetemperature • relative humidity during storage • gascomposition measured after packaging • the headspaceandproductvolumes • light conditions during storage. By using computer simulationsthe time for reaching, e.g., an oxygencontent critical for thecolour stability of a given product canbepredicted.Furthermore, demandsfor the permeabilityof the packagingmaterial canbe set,or the shelf life using aspecificpackagingfilm canbepredicted.Suchcomputer simulations weredevelopedby Pfeifferetal., (1999)primarily for predicting qualitychanges, moisturegainandlipid oxidation in severaldry products. The models described in the earlier sections arewell suitedfor defining critical factors andlevels for maintaining a goodmeatcolour stability of freshandcured meatproducts. 134 Meat processing Computersimulations are an attractive supplementto storageexperiments sinceit will not be necessaryto testall combinationsof the factors beforethe optimal packaging and storageconditions can be chosen considering both the product shelf life andminimisationof the packaging material. 6.9 References BERTELSEN G, JAKOBSEN M, JUNCHERD, MØLLER J, KRÖGER-OHLSEN M, WEBER C and SKIBSTED L H (2000), Oxidation, shelf-life and stability of meatand meatproducts, Proceedings 46th ICoMST, Argentina. BRO R (1997), PARAFAC. Tutorial and applications, Chemometrics and Intelligent Laboratory Systems, 38, 149–171. BROR andJAKOBSENM (2002), Exploring complex interactionsin designeddata usingGEMANOVA. Color changesin freshbeefduring storage, Journal of Chemometrics, 16, 294–304. DEVLIEGHERE F, DEBEVERE J and VAN IMPE J (1998), Concentrationof carbon dioxidein thewaterphaseasaparameterto modeltheeffectof amodified atmosphere on microorganisms. International Journal of Food Microbiology, 43, 105–113. FAVA P andPIERGIOVANNI L (1992),Carbondioxidesolubility in foodspackaged with modified atmosphere. II: Correlation with somechemical-physical characteristics andcomposition. IndustrieAlimentari, 31, 424–430. JAKOBSEN M and BERTELSEN G (2000), Colour stability and lipid oxidation of fresh beef. Developmentof a responsesurfacemodel for predicting the effects of temperature, storage time, and modif ied atmosphere composition, Meat Science, 54, 49–57. JAKOBSEN M andBERTELSENG (2002),Theuseof CO2 in packagingof freshred meatsand its effect on chemicalquality changesin the meat:A review. Journal of MuscleFoods, 13, 143–168. JENSENC, FLENSTEDJENSENM, SKIBSTEDL H andBERTELSENG (1998), Effectsof rapeseedoil, copper(B)sulphate andvitamin E on drip loss, colour and lipid oxidationof chilled porkchopspacked in atmosphericair or in ahigh oxygenatmosphere, Meat Science, 50(2), 211–221. LYIJYNEN T, HURME E, HEISKA K and AHVENAINEN R (1998), Towardsprecision food packaging by optimisation, VTT research notes 1915. MCDONALD K and SUN D (1999), Predictive food microbiology for the meat industry:a review, International Journal of FoodMicrobiology, 52,1–27. MØLLER J K S, JAKOBSEN M, WEBER C J, MARTINUSSEN T, SKIBSTED L H and BERTELSENG (2002), Optimizationof colour stability of curedhamduring packagingandretail displayby a multifactorial design, Meat Science, In press. PFEIFFER C, D’AUJOURD’HUI M, WALTER J, NUESSLI J and ESCHER F (1999), Optimizing food packaging andshelf life, Food Technology, 53,6, 52–59. RENERRE M (1990), Review: Factors involved in the discolorationof beefmeat, Modelling colour stability in meat 135 International Journal of Food Scienceand Technology, 25, 613–630. ROBERTSONG L (1993), Food packaging: Principles and practice, Chapter 4, Marcel Dekker, Inc. New York. WEBERJC, ALDANA L andBERTELSENG (1999).Inhibition of oxidative processes by low level of residual oxygen in modified atmospherepackaged pre- cooked cured and non-cured meat products during chil l storage. Proceedings of the 11th IAPRI World Conference on Packaging. Singapore.114–120. ZHAO Y, WELLS JH andMCMILL IN K W (1994),Applicationsof dynamic modified atmosphere packagingsystems for fresh red meats: Review, Journal of Muscle Foods, 5, 299–328. ZHAO Y, WELLS J H and MCMILLIN K W (1995), Dynamic changesof headspace gasesin CO2 andN2 packagedfreshbeef.Journal of Food Science, 60 (3), 571–557. 136 Meat processing 7.1 Introduction Fat is an essential component of meat for sensory perception of juiciness, flavour and texture. Fat in meat also supplies fatty acids that cannot be synthesised by humans. The perception of healthiness and sensory expectation are important quality criteria that influence the decision of a consumer to purchase a particular food product. Consumer perception of the influence of the content and composition of fat in meat, and in particular beef, for human health will be reviewed. Negative perceptions of beef as an excessively fat food have contributed to beef losing market share to competing meats and other protein sources throughout the developed world. Fresh meat production systems represent the combined and interacting effects of genotype, gender, age at slaughter and nutrition before slaughter, all of which can contribute to differences in the fat concentration of fresh meat. These influences will be briefly reviewed and it will be demonstrated that modern lean red meat can have an intramuscular fat concentration of 25–50 g/kg and can be considered a low-fat food. The opportunities to exploit the diet of meat animals to produce flavoursome meat that has an increased concentration of conjugated linoleic acid (CLA), a compound that may protect against obesity, cancer and heart disease, a low fat concentration and a fatty acid profile more compatible with current human dietary recommendations will be illustrated. The chapter will end with a commentary on likely future trends in the fat content of meat and meat products including the possibility of meat being recognised as a functional food. 7 The fat content of meat and meat products A. P. Moloney, Teagasc, Dunsany 7.2 Fat and the consumer The fat in meat supplies essential fatty acidsandvitamins andplays anessential role in the sensory perception of juiciness, flavour and texture. Nevertheless, thereis a perception amongconsumersandoftenthemedical professionthatred meat, in particular beef, is a food with an excessively high fat concentration. Further, meat fat is consideredto causea variety of human diseases, mainly becauseof thebelief that it hasa high proportion of saturatedfatty acids(SFA) which raise blood cholesterol levels, a risk factor for cardiovasculardisease (Departmentof Health,1994). Historically,animalproducts wereconsideredto be wholesome, versatile foods for humans and important for human health. From the 1960s however, attitudes towardsfatty foods beganto changeand animalfatswerelinked to theonsetof coronary heartdiseaseandotherdiseases. In 1984, the Committee on Medical Aspectsof Food Policy (COMA, 1984) publisheda report on diet in relation to cardiovasculardiseaseand this report andits successorshavebecomethebasisof public policy in theUK. Amongthe evidenceconsidered by the panel was the so-calleddirect evidence, i.e., the correlation found by Keys (1970) betweenmortality due to coronary heart diseaseandtheproportion of dietaryenergy derivedfrom saturatedfat in seven countries, selected from 21 for which datawereavailable. This conclusionhas been subjected to increasingcriticism (e.g. Blaxter and Webster, 1991) and HegstedandAusman(1988)demonstratedthat if Keys’ datafor JapanandItaly aredeletedthennostatistically significant correlationremainsbetween countries in the relationship between diet and coronary heart disease. Nevertheless, medical authorities world-wide recommendthat energy intake from fat should not exceed 30–35%,that energy intake from SFA shouldnot exceed10% of total energy intake and that energy intake from monounsaturated fatty acids (MUFA) andpolyunsaturatedfatty acids(PUFA) shouldbeapproximately 16% and7%, respectively, of energy intake.Furthermore, an increase in n-3 PUFA consumption such that the ratio of n-6:n-3 PUFA is Dataon the fat contentof a rangeof meat products arecompiled andpublished in food composition tables by several agencies, world-wide, so selected examples only are shown in Table 7.1. Fat in meat can be present as intermuscular fat (between the muscles),intramuscular fat (or marbling, i.e., within the muscles)and subcutaneous fat (under the skin). Most of the fat is presentasglycerolesters,but cholesterol, phospholipids andfatty acidestersare alsopresent.Due largely to

consumerpreferencefor low-fat food products, the red meat industry beganin the early 1980sto modify productionsystems to produce lessfat in meat.The fat contentof thecarcasshasdecreasedin Britain by over 30% for pork, makingmany pork cutscomparable with chicken, 15% for beef, and 10% for lamb, with further reductions anticipatedfor beef and lamb over the next 5–10 years(Higgs, 2000).Theseachievementsare due to selectivebreedingandfeedingpracticesdesignedto increase thecarcassleanto Table 7.1 Total fat andfatty acid concentrationof meatandmeatproducts(g/100g) (adaptedfrom Chanet al., 1995,1996) Fat SFA* MUFA* PUFA* Braisingsteak,lean,braised 9.7 4.1 4.1 0.6 Chickenbreast,skinless,grilled 2.2 0.6 1.0 0.4 Lamb leg, lean,roasted,medium 9.4 3.8 3.9 0.6 Liver, pig, stewed 8.1 2.5 1.3 2.2 Minced beef,extra lean,stewed 8.7 3.8 3.8 0.3 Pork loin chops,lean,roasted 10.1 3.7 4.0 1.5 Turkey thigh, casseroled 7.5 2.5 2.7 1.8 Bacon,back,fat trimmed,grilled 12.3 4.6 5.2 1.6 Chickenkorma 5.8 1.7 1.9 1.8 Chilli con carne,chilled/frozen,reheated 4.3 1.9 1.9 0.2 Ham, canned 4.5 1.6 2.0 0.4 Lamb kheema 14.5 3.8 5.3 4.2 Lamb kheema,reducedfat 9.7 3.4 3.6 1.8 Pork andbeefsausages,grilled 20.3 7.5 9.1 2.2 Pork sausages,reducedfat, grilled 13.8 4.9 5.9 2.1 Salami 39.2 14.6 17.7 4.4 Steakandkidney pie, singlecrust 16.4 6.1 6.7 2.5 Turkey pie, singlecrust 10.3 4.5 3.7 1.5 Extra-lean meat Beef, extratrimmed,lean 5.1 Beef, mini-joint 3.4 Beef, skirt steaks 6.9 Lamb, extra-trimmed,lean 7.5 Lamb, leg steaks 5.2 Lamb, medallions 8.0 Pork,extra-trimmed,lean 3.7 Pork,escalopes 1.7 Pork,medallions 3.9 *SFA = saturatedfatty acids,MUFA = monounsaturated fatty acids,PUFA= polyunsaturated fatty acids The fat content of meatandmeatproducts 139 fat ratio; official carcassclassification systems designed to favour leaner production; andmodernbutcherytechniques(seaming out whole muscles,and trimming away all intermuscular fat). Thesechangesareshownschematically in Fig. 7.1.Beefproducedduring our researchhada marbling fat concentrationin the orderof 20–50g/kg. This lean beefcould therefore be considereda low-fat food, especially when compared to the fat concentration presentedfor meatin many tablesof food composition(>70–100g/kg). The fat contentof meatproductscan vary considerably,dependingon the proportion of lean andfat from theoriginal meat aswell asthelevel of inclusion of otheringredients.Traditional meat productssuchassausages,pastry-covered piesandsalamiarehigh in fat (up to 50%) but modern productsincludeready meals andprepared meatsthat canbe low in fat (5%). The trenddownwards in fat for red meat is reflected in the reducedfat contentof a number of meat products, such as hams and sausages (Table 7.1). While reducedfat meat products are now available, the potential for productdevelopment in this area hasnot beenfully exploited. While themeatindustry continuesto addressconsumerpreferencefor lower- fat meatandmeatproducts, therelationship betweenthefat contentandsensory perceptionof meatmust beconsidered.In somemeatproduction systems (USA, Fig. 7.1 Reductionin fat contentof meat(After Higgs,2000). 140 Meat processing beef), high intramuscular fat content (marbling) has been associated with superiortenderness,juicinessand overall satisfaction. Moreover, many of the flavour compoundsof meatarecontained in the fat componentor arereleased due to chemicalchanges in the fat, alone and in interaction with the protein component,during ageingandcooking. Theconsensusof opinionnow is that a decreasein intramuscular fat to 2% will not impair eating quality of meat (Wood, 1990). This hasbeenobserved with pork loin or lean chicken breast (Chizzolini etal., 1999).A reductionin intramuscular fat contentto 2– 5%with a relatively greater reduction in ‘waste’ fat depots such as subcutaneous and intermuscular would make a positive contributionto production efficiency and consumerhealth without negatively impactingon meatquality. 7.3.2 Fatty acids Thefatty acidcompositionof selectedmeatandmeatproductsis alsoshownin Table7.1.Most meatsprovidesimilar proportionsof SFA andMUFA, making them an important sourceof the latter. While the ratio of PUFA to SFA is lower in ruminant tissuethan non-ruminanttissue,SFA representsless than half of the total fatty acidsof beefandof SFA, 30%arerepresentedby stearic acid which hasbeenshownto be neutralin its effect on plasmacholesterolin humans (Bonanomeand Grundy, 1988). This indicates that the common referenceto beef fat asvery saturatedis erroneous.Meat contributesto PUFA consumption,including docosahexaenoicacid and eicosapentaenoicacid of which therearefew rich sourcesapartfrom oil-rich fish. Docosahexaenoicacid hasan importantrole in the developmentof the centralnervoussystemof the newborn while eicosapentaenoicacid is involved in blood clotting and the inflammatory response.Meat from ruminant animals in particular, but also monogastricscanbea sourceof CLA (Section7.5.3).Thereis a growingbody of evidencethat a healthy diet which includes lean red meat can produce positive changesin lipid biochemistry.Blood cholesterollevels are increased by inclusion of fat, but not lean meat, in an otherwiselow-fat diet. Equal amountsof leanbeef,chickenandfish addedto low fat, low saturatedfat diets, simi larly reduce plasma cholesterol and LDL-cholesterol levels in hypercholesterolaemicand normocholesterolaemicmen and women. 7.4 Animal effectson the fat content and compositionof meat 7.4.1 Fatness An increasein fat depositionper se is generally accompanied by an increasein intramuscular fat concentration. The degree of fatness is determined by genotype, the weight of the carcassandhow closethe animal is to its ultimate mature size when slaughtered.In animal production systemswhich evolve to optimiseeconomic efficiency,severalof thesefactorsmay vary. The impactof thesefactors will be illustrated separately but likely interactions with the other The fat content of meatandmeatproducts 141 factors andnutrition (Section7.5) shouldalsobe considered.Acrossgenotype, breeds that have light mature bodyweights mature earlier than thosewith a heavier mature bodyweight.Therefore at a constanttime relativeto birth, earlier maturing animalswill befatter thanlatematuringanimals.This is illustrated by the dataof Keane (1993)shownin Table7.2 for different breedsof beefcattle. At 280kg carcassweight,Friesianshad18%fat. The corresponding proportion for Herefords,an earlier maturing breed was 21%, and for the later maturing Limousin, Charolais and Belgian Blue breeds were 16%, 12%, and 13% respectively. As carcassweight increased, the proportionsof fat increased and proportions of muscle and bone decreased.Compared with 280kg, a 400kg Friesian carcasshad 27% fat. Correspondingproportions for Herefords and Charolais were 31% and 21%, respectively. Intramuscular lipid proportion increased with increasing carcassweight and did so more rapidly for earlier- maturing breeds.For example, over the carcassweight range280–400kg, lipid concentration increasedby 51g/kg for Herefordscomparedwith an increase of only 21g/kg for BelgianBlues.Similar lipid concentrationswould be obtained from a Hereford carcassweighing 280kg and a Charolais carcassweighing 340kg. With respect to gender,heifers of the same breedgrown together with steersachieveda similar carcasscomposition at a lighter carcassweight(267vs. 326 kg) i.e., heifers are earlier maturing than steers (Keane,1993). Similarly, castration of intact male animals renders the resulting castrates more early maturing with respect to body composition. In general for anyparticular ratio, an increase in intakeby a meat-producing animal will promote a higher growth rate and a fatter carcass(at a similar carcassweight) i.e., growth rate per se will increasefat deposition relative to proteindeposition (Owenset al., 1995).This seemsto reflectsomemaximalrate of musclegrowth which appearsto be related to ageaswell asprotein intake Table 7.2 Fat concentration(g/kg) of beefcarcassand longissimusdorsi muscle (adaptedfrom Keane,1993) Carcassweight(kg) 280 340 400 Sire Sub. IM. Sub. IM. Sub. IM. Breed(a) Fat(b) Fat(c) LD(d) Fat(b) Fat(c) LD Fat(b) Fat(c) LD Friesian 77 104 22 102 123 43 130 138 67 Hereford 91 114 26 121 134 50 155 150 77 MRI 76 102 22 98 120 46 123 135 73 Limousin 65 90 20 86 109 35 109 126 53 Blonde 53 74 16 72 90 25 92 105 37 Simmental 61 87 18 82 104 30 105 119 45 BelgianBlue 53 76 16 71 91 25 89 106 37 Charolais 55 80 16 74 96 28 95 110 43 (a)Matedto Friesiancows(b) Subcutaneousfat (c) Intermuscular fat (d) Longissimus dorsi muscle 142 Meat processing (Basset al., 1990).However, thereis some opportunity to decreasefatnessby manipulating the growth pathrelatively close to slaughter. ThusMoloney et al. (2001) reported that compared to cattle finished on a grass silage and concentrateration, feeding unsupplementedsilagefor 56 daysfollowed by the sameamountof concentratesoffered ad libitum decreased internal fat weight and longissimus dorsi lipid concentration. Practical methodsof decreasing fatnessin farm animalshavebeenreviewed (Basset al., 1990). 7.4.2 Fatty acids Manycomparisonsof animalfactorsareconfoundedby differences in fatness. In general, increasingfatnessresults in greater unsaturation of lipid with the MUFA proportion increasing and SFA proportion decreasing(Duckett et al., 1993). However, where corrections have been made for fatness, some differences in fatty acid composition due to genotype have been reported. Zambayashiet al. (1995)suggestedthat theJapaneseBlack breedof cattle hasa geneticpredisposition for producing lipids with higher MUFA concentrations than other breeds studied. The Wagyu beef breedis characterisedby greater intramuscular than subcutaneous fat deposition and was found to havehigher concentrationsof MUFA and a higher MUFA:SFA ratio than other breedsin several studies (Xie et al., 1996). Similarly for pigs, the Duroc breed, characterisedby higher amountsof intramuscular fat relative to backfat, had higherintramuscular SFA andMUFA proportionsandlower PUFA proportions than British Landrace pigs (Cameron and Enser, 1991). In both breeds, increasing intramuscularfat deposition caused a relativelygreaterincrease in the MUFA proportion than the SFA proportion.Breed differences and effects of maturity or growth stage on the subcutaneousor intramuscular fatty acid composition of beefhavebeenreviewedby deSmetetal. (2001).With regard to gender, fewer comparisons have been made but Malau-Aduli et al. (1998) reported phospholipid PUFA:SFA ratios of 0.27 and0.54 for steer andheifers respectively, fed on pasture. Specific breeddifferences in then-6:n-3PUFA ratio andin theconcentration of longerchainn-3 PUFA thatprobably couldnot beattributedto differences in intramuscular fat concentration have also been reported.Choi et al. (2000) reported significantly higher proportions of C18:3n-3 in neutral lipids and phospholipids andhigherproportionsof C20:5n-3andC22:5n-3in phospholipids of WelshBlack compared with Holstein Friesiancattle, resulting in a lower n-6:n-3 ratio in WelshBlack, whereastherewereno differences in theconcentrationsof C18:3n-3 and C22:6n-3. The preferentialdeposition of n-3 PUFA wasmaintained on diets containing supplemental n-3 PUFA, indicating no breed by diet interaction. Itoh et al. (1999) found significant differencesbetweenAngusand Simmental cattlein thedeposition of C18:3n-3andof thelonger chain fatty acids, but breed by diet interactionswerepresentfor some of thefatty acids,makingit difficul t to interpret the

breedeffects.Despitethe above,de Smetet al. (2001) concludedthatmuch of thedifferencesin fatty acidcompositionapparently due The fat content of meatandmeatproducts 143 to genotypecould be explainedby variation in intramuscular fat concentration and that effects of genotypewere in general much smaller than effectsdue to diet. 7.5 Dietary effectson the fat content and compositionof meat 7.5.1 Fatness Whenexamining the effectsof diet on the fat content of meatit is importantto separatethedirecteffectsof dietary ingredientsfrom indirecteffectsof possible differencesin energy intake on carcassweight and fatness. Carcass fatnessin monogastrics and ruminants can be influenced by the energy and protein concentrationin thediet.However, theextentto which theproportionof lean-to- fat is alteredby dietary manipulations is limited without havinga major impact on growth rate and feed efficiency. In pigs, restricting the energy intake by feeding a low-energy (low fat and/or high fibre) diet will reducecarcassfat deposition. Other nutrients must be supplied in sufficient amountsto support maximum lean tissueaccretionor restriction in energy intake may result in protein being used for energy purposes. Feeding excessprotein, i.e., excess essential aminoacids,to pigs will result in a higherproportionof lean to fat in the carcassbut the effect is primarily a result of energy restriction relative to protein.Changesin intramuscularfat concentrationcanalsobeaccomplishedby varying the energy and protein composition of the diet. Knowledgeof energy and amino acid nutrition of ruminants is not as advanced as for monogastrics mainly dueto pre-fermentation andtransformation of dietary ingredientsin the rumen of ruminants. Nevertheless, there is a body of evidence that unwilted, extensively fermented grasssilage can increase fatnessrelative to wilted silage/hay or non-silage-baseddietsandthat starchy ingredientspromote greater fatnessthan digestible fibre-based ingredients. In a grass silage-based ration, protein supplied in excess of requirement increasedcarcassfatness(SteenandRobson, 1995). Increasing propionate supply from the rumen by addition of sodium propionateto the diet decreased fat deposition (Moloney, 1998; 2002). Many studies have compared the effects of foragebased diets with concentrate (usually grain) -baseddiets.In a literaturesurvey,Muir et al. (1998)foundlittle differencein marblingbetween grain-fedandgrass-fedbeefat thesamecarcass weight. This conclusionis supported by French et al. (2000). 7.5.2 Fatty acids Fatty acid deposition in monogastrics largely reflects dietary fatty acid composition (Wood and Enser, 1997,Rule et al., 1995).This is illustratedby datafrom Verbekeet al. (1999)shown in Table 7.3. Intramuscular fat in pigs hadhighMUFA reflectingendogenoussynthesisbut incorporation of oilseedsin the diet can increase the PUFA:SFA anddecreasethe n-6:n-3PUFA ratio. An 144 Meat processing importantdifferencebetween monogastricsandruminantsis that the long-chain n-3 PUFA, including eicosapentaenoic acid anddocosahexaenoic acid, arenot incorporatedinto triacylglycerols to anyimportantextentin ruminants.Theyare incorporated mainly into membrane phospholipids and therefore, are found predominantly in muscle(Enser et al. 1996).This providesthe opportunity to manipulateintramuscularfatty acidcomposition of ruminantmeatwithout large increases in fatnessper se. In ruminants, dietary PUFA are hydrogenated to SFA but a proportion of dietary unsaturated fatty acidsbypasses the rumenintact and is absorbed and deposited in body fat (Wood andEnser,1997). Increasing the dietarysupply of PUFA, particularly n-3 PUFA, is onestrategyto increase PUFA concentrations in ruminantmeat.In Table 7.4, inclusion of bruisedwhole linseed,a rich source of linolenic acid,resultedin 100%increase in concentrationof linolenic acid in musclewhile a linseed oil-f ish oil treatment increased the marine n-3 PUFA concentrations(Scollan et al. 1997;2000).The fatty acid composition of beef can be more efficiently modified by including in the diet, fatty acidsthat are protectedfrom ruminal hydrogenation(Scottet al. 1971, Demeyer andDoreau, 1999).Scollanet al. (2001)showedthat a protectedlipid supplement markedly improved the PUFA:SFA ratio in muscle (Table 7.4). Grasshas higher PUFA and particularly higher n-3 PUFA, primarily as linolenic acid, than grain-basedruminant feeds. In general, grass-fedbeef has higher concentrationsof PUFA, particularly in the phospholipid fraction, than grain-fedbeef(Griebenow et al., 1997).An increasein theproportionof grass in the diet of finishing steers decreasedthe SFA concentration, increasedthe PUFA:SFA ratio, increased the n-3 PUFA concentration and decreased the n- 6:n-3PUFAratio (Frenchet al., 2000).Then-3PUFAdetectedin meat from the grass-fed cattle in this study was predominantly linolenic acid. The health benefits of n-3 PUFA from plant and marine (i.e. longer chain fatty acids) sourcesappear to differ. An expert workshopon this issue(de Deckere et al., 1998)concludedthat: thereis incompletebut growing evidencethat consumption of the plant n-3 PUFA, alpha-linolenic acid, reducesthe risk of coronary heart disease. An intakeof 2g/d or 1% of energyof alpha-linolenic acid Table 7.3 Influenceof fat sourceson fatty acid compositionof pig muscle(adapted from Verbekeet al., 1999) Fat source Fatty acids Tallow Rapeseed Soybeans Linseed Safflower C18:1(%) 44.06 46.55 38.75 38.17 48.8 C18:2(%) 10.36 10.54 14.98 10.68 10.4 C18:3(%) 0.52 1.11 1.04 4.41 1.40 PUFA:SFA 0.30 0.32 0.37 0.36 0.34 n-6:n-3 19.92 9.50 14.40 2.42 7.43 The fat content of meatandmeatproducts 145 appears prudent. The ratio of total n-3 over n-6 PUFA (linoleic acid) is not useful for characterising foodsor dietsbecauseplant andmarinen-3 PUFA showdifferenteffects,andbecausea decreasein n-6 PUFA intakedoesnot produce the same effectsasan increasein n-3 PUFA intake.Separaterecommendations for alpha-linolenic acid, marine n-3 PUFA and linoleic acid arepreferred. Grass-fed beef can contribute to diets designed to achieve an increased consumption of n-3 PUFA. 7.5.3 Conjugated linoleic acid Conjugatedlinoleic acid (CLA) refersto a mixture of positionaland geometric isomersof linoleic acid (18:2 n-6). The cis 9, trans11 form is believedto be the mostcommonnaturalform of CLA with biologicalactivity, butbiologicalactivity Table 7.4 Influenceof fat sourceson the fatty acid composition(mg/100gtissue)of beefmuscle(adaptedfrom Scollanet al., 1997;2000;2001) (i) Different sourcesof oil Fatty acids Control Linseed Fish oil Linseed/fishoil s.e.d. Significance C16:0 1029 1089 1305 1171 206.0 NS C18:0 528 581 543 490 104.0 NS C18:1 1209 1471 1260 1225 279.0 NS C18:2 81 78 66 64 9.2 NS C18:3 22 43 26 30 5.6 ** C20:4 23 21 14 17 1.5 *** C20:5 11 16 23 15 1.9 *** C22:6 2.2 2.4 4.6 4.9 0.52 *** Total fatty acids 3529 4222 4292 3973 741.0 NS PUFA:SFA 0.07 0.07 0.05 0.05 0.011 NS n-6:n-3 2.00 1.19 0.91 1.11 0.141 ** (ii) Oil protectedfrom ruminal biohyrogenation Fatty acids Control 500gPLSy 1000gPLSy s.e.d. Significance C16:0 986 843 598 117.8 * C18:0 508 421 331 61.6 * C18:1 1195 1144 759 177.0 * C18:2 100 195 215 9.5 ** C18:3 23 46 46 4.3 ** C20:4 28 27 28 2.0 NS C20:5 10 10 9 1.2 NS C22:6 2 2 2 0.4 NS Total fatty acids 3505 3260 2421 430.8 * PUFA:SFA 0.06 0.19 0.28 0.029 ** n-6:n-3 4.6 4.4 4.7 0.48 NS Notes * = p< 0:05, ** = p< 0:01, *** = p< 0:001 y= protectedlipid supplement. 146 Meat processing has been proposedfor other isomers,especially the trans 10, cis 12 isomer. Conjugatedlinoleic acid hasbeenshownto be an anticarcinogen,and to have antiatherogenic, immunomodulating, growth promoting, lean body mass- enhancing and antidiabetic properties (MacDonald, 2000; Whigham et al., 2000).It is foundin highestconcentrationsin fat from ruminantanimals,whereit is producedin the rumen as the first intermediatein the biohydrogenationof dietary linoleic acid. In the secondstepof the pathway,the conjugateddieneis hydrogenatedto trans 11 octadecenoicacid (trans-vaccinicacid) which is now thoughtto beasubstratefor tissuesynthesisof CLA via anenzymaticdesaturation reaction.Becauseof thepotentialhealthbenefitsarisingfrom CLA consumption, there is considerableresearcheffort directedto increasingthe CLA contentof ruminant-derivedfood. Milk fat CLA concentrationsareprimarily influencedby linoleic acid supply to the rumen,by inclusion of grassin the diet and by the forageto concentrateratio of the diet (Kelly et al., 1998a,b; Jianget al., 1996). For ruminantmeat,an increase in theproportion of grass in thediet causeda linear increasein CLA concentration, while a grasssilage/concentrate diet resultedin a lower CLA concentration than a grass-baseddiet with a similar forageto concentrate ratio (Frenchet al., 2000). Inclusionof sunfloweroil in the supplementaryconcentrateto a silage-based diet alsolinearly increased muscle CLA (Noci et al., 2002).Concentrationsof CLA in Irish andAustralianbeefcan be two to threetimes higher thanthosein United Statesbeef. This presumably reflectsthe greater consumption of PUFA-rich pasturethroughoutthe year by cattle in these countries. Protection of dietary CLA from ruminal biohydrogenation is being examined with equivocal results. Gassmanet al. (2000)reported a 2.4 and3.0-fold increasein intramuscularCLA concentration in rib androundmuscle, respectively, in responseto inclusion of 2.5%protected CLA in the diet of cattle. Dietary inclusion of CLA has also beenshown to markedly increasethe CLA concentration of pig muscle(from 0.09 to 0.55% total fatty acids in the study of Eggert et al., 2001) and chicken muscle. In addition, thereis evidencethattheCLA concentrationincreasesin foodsthatare cookedand/or otherwise processed. 7.6 Future trends In the UK between1989 and 1999, consumptionof primary poultry meat and other meat productsincreasedwhile that of carcassmeat (beef, veal, mutton, lamb, and pork) declined (Robinson,2001). Robinson(2001) consideredthis increasein consumptionto beduemainly ‘to increasesin meatbasedreadymeats and takeaways eaten at home’. This clearly reflects consumer desire for convenienceproductsand presentsa major challengeto the non-poultrysector andto theprimered-meatsector,in particular.To regainmarketshare,this sector of the meatindustrywill haveto developa morediverserangeof products. The declinein carcassmeatconsumption also reflects consumerpreference for low-fat meat and meat products, guided by medical advice. Recent The fat content of meatandmeatproducts 147 developmentsin decreasingthetotal fat concentrationof meat andmanipulating the fatty acid concentration have been illustrated in earlier sectionsof this chapter. Thereare clear opportunitiesto manipulate the animal componentof fatnessby integratingthe variouscontributingfactors, i.e., breed selection,use of noncastratedmaleanimals,slaughteredyoungandfedappropriately,etc.It is likely that the nutrient requirements to optimise protein accretion while minimising adiposetissue accretion will be defined more precisely than at present. Current and future research will then focus on optimising both the supply of nutrientsandthetimewhen theyaresupplied (bothdiurally andduring the lifetime of the animal) to allow the targetanimal to achieveits genetically determinedbody andmuscle composition. The data presentedon factors affecting the fatty acid composition of the intramuscularfat of meatdemonstratethatmeat canbe producedthathasa fatty acid profile morecompatiblewith currentmedical recommendationsfor human diet composition. In

particular, red meatscannow be producedthat are low in fat, havea lower concentration of atherogenic SFA, higher MUFA andPUFA concentrations and lower n-6:n-3 PUFA ratio than was possible previously. Moreover, thereis emerging evidencethat palmitic acid andstearic acid do not contribute to coronaryheartdiseaseindicating that the perception that all SFA are ‘unhealthy’ is incorrect. Sincemeatintramuscular fat containsvirtually no short chain SFA, only myristic acid contributes to elevated low density lipoproteincholesterol,a risk factor for coronaryheartdiseaseandthis typically representsjust 3% of total fatty acids. Since n-6:n-3 PUFA ratio in meat is within thedesirable range,futureresearch will focuson enhancing thefatty acid profile of meat even further, in particular with the use of emergingrumen protection technology. Parallel research will be required to ensure adequate antioxidantprotection in meatwith an improved PUFA:SFA ratio. The so-called ‘lipid hypothesis’ hasguidedmedical advice for many years. This hypothesisis beingincreasingly criticised,particularly ason-goingresearch on lipid metabolism in humansandits relationship to healthanddiseaseyields datainconsistentwith this hypothesis.Moreover, the hypothesisthat a low-fat, high-carbohydratediet is bestfor preventing obesity, adisorderoftenconsidered to reflect fat consumption, is alsobeingincreasingly rejected.It is to be hoped that future medical guidelines will reflect the findings of recent dietary intervention-type research rather than be basedpredominantly on correlations arising from epidemiological, rather than retrospective-type studies. The discovery of CLA, together with the finding that ruminant fat is its primary natural source, is a positive advance for red meat,in particular. Clarification of thehealth-enhancing anddisease-preventing propertiesof CLA in humansis the subject of extensive research world-wide. Reproduction in humans, of the observationsmade in laboratoryanimalmodels and tissueculture, will greatly add to the imageof meatas a healthy food. Moreover, future meatcould be considereda functional food, i.e., a food that hashealth benefitsbeyondbasic nutrition. The American Dietetic Association hasendorsedleanbeefand lamb as functional foods (1999). Researchon strategies to increase the CLA 148 Meat processing concentrationin meatwill continueandtheobservation thatCLA is depositedin adiposetissueas well as the intramuscular phospholipid fraction will provide high CLA fat as a functional ingredient for healthy processed meats (see Jimenez– Colmenero et al., 2001). Thepositivecontribution of meatto humandiet andrecognition that evenat present, meat has a role in a healthy diet is not appreciated by consumers (Bruhn, 2000). Of consumers surveyed in the US (American Dietetic Association, 1997), fish was perceived as very healthful by 57% and poultry by 55%, but meat suchasbeef, pork, and lamb wasseenasvery healthful by only 13%; an additional 45% consideredit somewhat healthful. Bruhn (2000) statesthat the potential for health-enhancing productsis substantial. Enhanced nutritional components in animal products meet the preferencesof consumers and healthprofessionals.There is a neednow and in the future for the meat industry to conveythepositive nutritional contributionsof meatproductssuchas iron, zinc, ‘healthy’ fatty acids and CLA to both consumers and health professionals.Theconclusionof Bruhn(2000)that‘communicationis thekey to correct consumer(and medical) myths and to increase awareness of new information or enhancedpropertiesof healthful food’ is mostappropriateadvice to all sectorsof the meatindustry for the future. 7.7 Sourcesof infor mation and advice Publications GURR,M.I. (1999)Lipids in Nutrition andHeath:A Reappraisal. TheOily Press, Bridgwater. ATKINS, R.C. NewDiet Revolution. Vermilion, London. ALLEN, P., DREELING, N., DESMOND, E., HUGHES, E., MULLEN, A.M. and TROY, D. (1999)New Technologiesin the Manufacture of Low Fat Meat Products. End of project report. The National FoodCentre,Dublin. MEAT IN THE DIET. Briefing paper.The British Nutrition Foundation, London. MCCANCE AND WIDDOWSON’S TheComposition of Foods.The Royal Society of Chemistry and Ministry of Agriculture, Fisheries and Food (and supplements). NEWMAN, C., HENCHION, M. and MATTHEWS, A. (2002) Factors shaping expenditureon meat and prepared meals.End of project report. The NationalFoodCentre, Dublin. 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(1996) Effects of breed and sire on carcass characteristics and fatty acid profiles and crossbredWagyu and Angus steers.Meat Science43, 167–177. ZAMBAYASHI, M., NISHIMURA, K., LUNT, D.K. andSMITH, S.B. (1995)Effect of breed type and sex on the fatty acid composition of subcutaneous and intramuscular lipids of finishing steers and heifers. Journal of Animal Science73, 3325–3332. The fat content of meatandmeatproducts 153 Part II Measuring quality 8.1 Introduction To be able to define the quality indicators for raw meat it is neccesary first to define what quality of meat is. The quality of raw meat can be defined as the suitability of meat for use in a specified product. If the meat is well suited for the product it is intended for, then the meat quality is defined as good. If the meat is less suitable for the product, then the meat quality is defined as poor. The attributes of meat that determine the quality thus depend on the use for which the meat is intended. Quality can be defined astechnological quality, describing meat for further processing like salting, curing, etc., or asfresh meat eating quality that describes meat for fresh meat consumption, and which includes all traits registered with our senses, both appearance, flavour and texture. The quality indicators for the two quality definitions to some degree overlap but some differences also exist. Other quality descriptions, however, exist like ethical quality and health quality but they will not be covered in this chapter. 8.2 Technological quality In the processing of meat the yield is the main quality parameter as it determines the amount of available product for sale and is therefore of direct economic importance. The sensory quality of the processed product has an indirect economic importance as it might influence the amount of sold product, especially how often a consumer buys the same product again. Quality indicators in the raw meat that can predict the yield of the processed meat are 8 Quality indicators for raw meat M. D. Aaslyng, Danish Meat Research Institute, Roskilde especially pH and water-holding capacity, whereasthe sensory quality of the processedmeatcan also be influencedby the colour, the meat/fat distribution andthe fat quality in the raw meat. 8.2.1 pH and water-holding capacity The yield of curedcookedproductsdepends on the pH of the meat. The higher pH the higher yield (Müller, 1991). In an investigation of hams produced without phosphates the correlation between pH and total yield wasaround0.4 (Table 8.1,unpublisheddata,Hviid, 2002pers. comm.). Production of this type of hamincludesacuringandacookingstep.An investigationhasshownthatthe pH especially influencesthe yield by alteringthe cooking loss.The hams were from non-carrier andcarrier pigs of the RNÿ-geneandwereproduced without phosphates. Pigscarrying theRNÿ-genearerecognisedby havinghighglycogen content,high drip loss, andlow pH. Thecuringyield wasindependent of genetic background and therebyof pH, whereasthe carriers of the RNÿ-genehad a significantly highercookingloss(Anderssonet al., 1997). Not only theyield but also the colour can be influenced by pH. In cured bacon product the pH influencedthe colour of the bacon.A pH below 5.3 resulted in baconof an unevencolor whereaspH above5.7 gavea beefy, glazy appearance(Barton, 1971). If the water-holding capacityis extreme like PSE(pale, soft exudative) or DFD (dark, firm, dry) meatit is also reflected in the yield PSEmeatgiving a lower yield and DFD meat giving a higher yield compared to normal meat (Barton Gade,1984). Also dried hams with a 12-month seasontime show a higher weight loss if the raw ham was PSE (Maggi and Oddi, 1988). The relationshipbetweendrip lossandyield in productionof hamsfrom meathaving a water-holding capacityin a more normal rangeis howeverrelatively low as canbe seenfrom Table8.1 with a correlationbelow 0.3. The water-holding capacity andpH is very dependenton the pre- andpost- slaughter metabolism. A fast pH decline early post-mortem has often been shown to result in low water-holding capacity. In theseworks the pH hasbeen determined45 minutepost-mortemanda low pH hasbeensaid to be dueto a fast pH decline. Recent investigations where the pH wasdetermined already1 minute after debleedinghave shown that it might not be the rate of the pH Table 8.1 Correlation between meat quality and cooking loss/total yield in an investigationof hamsproducedasJambonSuperieur(without phosphates)of meatfrom LYD, LYDH andLYP pigs all free of the halothanegeneandthe RNÿ-gene(nˆ 315) (Hviid, 2002,unpubl.data). Cooking loss Total yield pH ÿ0.437 0.394 Drip loss 0.277 ÿ0.286 158 Meat processing declinebut the timeof accelerationof thepH declinewhich is crucial (Henckel et al., 1999;Støieret al., 2001). In animals with a high pre-slaughter stressthe pH of the muscles was lower alreadyat time of slaughter compared to less stressed animals (Henckel et al . 1999). When the concentration of creatinephosphate at the time of slaughter is high the anaerobic glycogen degradation and thereby the lactate production will occur later and the acceleration of the pH decline will therefore be delayed (Støier et al. 2001). Both investigations find, however, that the rate of pH decline was equally independent of preslaughter stress.pHu is independent of the pH decline. Insteadthelimi ting factorfor theultimatepH is theconcentrationof glycogenin themuscles(Henckel et al., 1997).If thepigsareexhaustedat slaughterthelow glycogencontentwill resultin a high ultimatepH andthemeat will beDFD. In a more normal pH interval a linear correlation betweenpHu and the glycogen contentat slaughterhasbeenseenat concentrationslower thanabout53 mmol/ kg. With moreglycogenno correlationwasseen(Henckel, Pers.Comm.). pH is aneasilydeterminedrawmeatquality attribute.It canbedeterminedby direct measurement with an electrode in the meat, or a sample can be homogenised before determination. The water-holding capacity can be determinedby threefundamentallydifferentprinciples:(i) usingexternal forces to drive out the water like the filter press methodandby centrifugation, (ii) by letting the waterdrip out of the raw meatin a standardisedway over a certain time periodlike the‘Honikel bagmethod’or theEZ-drip loss, or (iii) by heating the meatandmeasuring the cooking loss(Honikel, 1989;Honikel andHamm, 1994;RasmussenandAndersson, 1996;Christensen,2002). 8.2.2 Colour Thecolour of theraw meatis acombinationof thecontentof myoglobin andthe reflection from theprotein denaturation. For thecolourof thecured cookedmeat only the content of myoglobin is important. During the curing processthe myoglobin and oxymyoglobin are converted into nitrosomyoglobin in the presenceof nitrite, formingapink colour (Andersenetal., 1988).During storage thecolour might furtherchangebut it depends on boththepackagematerialand on thepackagingandstorageconditions(Andersenet al. 1988).Theamountof myoglobin in the raw meat might thereforebe an indicator of the raw meat quality with respectto further processing. The hem-group of both myoglobin andtracesof hemoglobine canbe quantified spectrophotometrically. 8.2.3 Meat/fat distri bution and fat quality Thefat contentandquality of theraw meat is alsoan indicatorof thequality of processed meat.Cookedcuredhamis in generalregardedasa lean meatproduct in France.Theamountof intramuscularfat (IMF) in

Frenchhamsdid notchange other sensory attributes than colour and marbling when assessedby a trained sensory panel but acceptability by consumers decreased markedly with Quality indicatorsfor raw meat 159 increasing IMF (Fernandez et al., 2000). In dried, cured meatproduct a high amount of intramuscular fat is, however, demanded(Garcia et al., 1997). A study of dry cured pork ham comparingthreeterminal siresshowedhowever that Duroc and Large White as terminal sire gave the same consumer acceptability independent of a larger IMF content in Duroc (Oliver et al., 1994).In bacon,especially, the lean/fatdistribution is importantto consumers. Most Irish consumers prefer a thin fat layer (44%) followed by medium fat (38%) andvery thin fat (17%). On this backgrounda back fat depth of 12–16 mm was recommended as optimal for most of this consumer group (Moss, 1993).As morefocushasbeenon thehealthperspective of fat intakethis might havechangedtowards a thinner fat layer sincethis investigation. Fatty acid composition influencesthe quality of meat as well in respect to processedmeat quality. A high content of polyunsaturated fatty acids like linoleic acid (C18:2) and n-3 fatty acids results in softening of the fat and a higher oxidative instability. As fat rancidity is one of the limiting factors in storageof productswith fat-like sausagesthis is of importanceaswell (Woo and Maeng, 1983).If the animalsarefed with vitamin E, the antioxidativestatusof the meat will however be increased andtherebylimit the problem of rancidity while Cu in the feedwill act asa prooxidant andtherebyincreasethe problem with rancidity (Lauridsenet al., 1999). IMF canbemeasuredvisually asfat marbling using differentscales.This is a subjectivemethodbut with photos asreferencesit is possibleto standardise the assessment. By chemical analyses the content of IMF can be described objectively. Most chemical methodsbegin with an acid hydrolysis, to liberate the fat from proteinsandother complexes,followed by an extraction step.This step determines which part of the lipids the later analysis will quantify. It is possible to get the neutrallipids (triglycerides)only or in additiona greateror smaller part of the phospholipids (polar lipids from the membrane). The phospholipid content ranges from about0.5% in longissimusdorsi (LD) up to about 0.7% in psoasmajor and 0.9% in masseter in pig (Gandemer, 1999; Mourot andHermier, 2001).In beefthecontentof phospholipids is about0.7% in longissimus dorsi and 1.1% in diaphragma (Gandemer, 1999). The concentration of phospholipids in a muscle is rather invariable compared to the contentof triglycerides,which canvary. After the extractionthe amount of lipids canthenbequantified gravimetrically. It is alsopossibleto determine the amount of fat by methods like NMR. The fatty acid composition can be determinedon an extractof the meat by GC. 8.3 Eating quality Whenmeatis usedfor freshconsumption thetime from slaughter to counter can rangefrom two days(in particular poultry and pork) to several weeks(in the case of beef). The appearance of the raw meat influences the consumer’s willin gnessto buy the meat, and can therefore be regardedas an important 160 Meat processing quality factor for meat proposedfor fresh meat consumption. However after cooking tenderness,juiciness, flavour, and appearance of the cooked meat together determine the eatingquality. Quality indicators of raw meat for these parameters are the content of intramuscular fat and the composition of fatty acids, the collagen content and solubility, the sarcomere length, activity of proteolytic enzymes, pH andwater-holding capacity,andthe colour of the raw meat. 8.3.1 Intra muscular fat and fatty acid composition The content of intramuscular fat or the degreeof fat marbling has a great influenceon the eatingquality beginning whenthe consumers choosethe meat in the supermarket. Many consumers will rejectbuyingmeat with a medium or high amount of visual fat marbling both in beefandpork eventhoughthey find it morepalatablewheneatenwithout knowingtheamountof fat (Grunert, 1997; Bredahl et al., 1998;Brewer et al., 2001a), Bligaard,2002,Pers. comm.). Thereareconflicting resultson the influenceof IMF on tenderness.It is said to increaseboth the tendernessof the meat(DeVol et al., 1988; Cameron and Enser, 1991;Gwartney et al., 1996;Fernandezet al., 1999;CandekPotokaret al., 1999;Laacket al., 2001;Breweret al., 2001a;D’SouzaandMullan, 2002) and to have no effect or even a negative effect (Göranssonet al., 1992; Kipfmüller et al., 2000).Thereasonfor theseresults could be,thatvariations in IMF arealwaysconfoundedwith othervariations,which alsohavesignificance for tenderness.The age of slaughter and the slaughter weight influence the contentof IMF (Johnsonet al., 1969;Candek-Potokaret al., 1999)but canalso influence factors li ke the content and strengthof connectivetissueand in this way influence the tenderness. Feedingstrategynot only influences the IMF content (Blanchard et al., 1999) but also the growth rate and thereby the proteolytic activity that is of significance for the tenderisation of the meat during ageing (Therkildsen et al., 2002). The genetic background also contributesto variations in IMF. In pork somebreeds li ke the Chinesebreeds and Berkshire have an extremely high fat content. In the more commercial breedsDurocespecially is known to havea higher contentof IMF comparedto the white breeds li ke Landraceand Large White. It hasbeenshownhowever, that the correlation between IMF and sensory quality depends on breed (FjelknerModig and Persson,1986). The fatty acid composition can also influence the effect of IMF on tenderness. In pork the saturated and monounsaturated fatty acids are positively correlated to tenderness where polyunsaturatedfatty acids are negatively correlated to tenderness(Cameron and Enser,1991; Eikelenboom et al., 1996). The fatty acid composition is dependent on both breed (Garcia et al., 1986; Tejeda et al., 2001) and feed (Engel et al., 2001). It hasalsobeensaidthata high contentof IMF would improve therobustness of the meat against a non-optimal cooking. This was shown in beef by Cummings et al., (1999)who found a decline in tendernessin meatwith a low Quality indicatorsfor raw meat 161 IMF contentwhencookedto 80ºCwhile meatwith a high IMF contentwasstill tender at this end-point temperature.The differencebetween the two groupsat 70ºCend-point temperaturewasonly small. It wasnot possible to find a similar effect in anotherstudy (Rymill et al., 1997) and the effect of IMF on the robustnessof the meat might therefore interactwith other matters,asthe direct effect of IMF on tendernessis said to do. Juiciness is the feeling of moisture in the mouth during chewing. It is a dynamic attribute changingduring the chewing process.The contentof IMF is positively correlatedto juiciness(Savell andCross,1988;Gwartneyet al. 1996; Flores et al., 1999; Cummings et al., 1999; Brewer et al. 2001a). Some investigationsindicateespecially that thesustainedjuicinessexperiencedduring the last part of the chewing process,is increased by increasingamount of IMF (Savell and Cross,1988; Aaslyng et al., 2002).An increasing amountof IMF also implies a decreasein cooking loss (Aaslyng et al., 2002). Juiciness is to some extent negativelycorrelated to cooking loss (Tornbergand Göransson, 1994;Toscaset al., 1999; Aaslyng et al., 2002)andthe decreased cookingloss could explain part of the effect of IMF on juiciness. The contentof IMF also influencesthe flavour of meat(Candek-Potokaret al., 1998;Fernandezet al. 1999).This might be due to production of a volatile componentasthe fatty acidcomposition is importantto the flavour. In pork the contentof polyunsaturated fatty acidsis correlatedwith abnormal flavour while monounsatuated and saturatedfatty acids are correlatedwith pork flavour and overall liking (CameronandEnser, 1991;Cameronet al., 2000).In beef it has beenfound that the meatyaromawas due to phospholipids and not to sucha great extent to triglycerides (Mottram and Edwards, 1983). Flavour is a compositionof volatile andnonvolatile components. It is not investigatedhow IMF influencesthe nonvolatile flavour components but part of the unspecified effect on flavour could be due to facilitating the contact between the flavour componentsandthe taste buds. 8.3.2 Connective tissue It is well known that musclesrich in connective tissuelike bicepsfemoris are less tenderthanmusclescontaining less connectivetissuelike psoasmajor and the connectivetissuehastherefore often beenin focus as a contributor to the toughnessof the meat and therefore a raw meat quality indicator (Honikel, 1992).The main constitutent of the connective tissueis collagen. Collagenis a very strongprotein polymereand it is said to makeup about2% of the total muscle protein in beef(Powell et al., 2000).Collagencanbedivided into a heat soluble and a heat insoluble fraction reflecting the degreeof cross-linking of hydroxyprolin in the collagen(Powell et al., 2000). Ageing of the meataltersthe connectivetissueonly marginally (Nordyke et al., 2000) and part of the effect might actually be due to degradationsof the proteoglycansin integrity with the connective tissue.The collagen molecules change during cooking and their influence on meat tenderness is much 162 Meat processing influenced by the end-point temperature and the heating rate (Powell et al., 2000). Thedegreeof cross-linking of collagen increaseswith theageof theanimal. At the sametime the shearforce increasesindicating a decreasein tenderness (Lebret et al., 1998; Fanget al., 1999). Also feeding can alter the degree of cross-linking. In beefa high energylevel up to slaughter results in anincreasein heat-soluble collagenand a decreasein shearforce (Miller and Cross,1987; Schnell et al., 1997). In a shearforce determination the meat is heatedin a controlled way, and depending on the end-point temperature the heatsoluble collagen will no longer add to the shearforce. The effect of cross-linking on tenderness is, however, not that clearcut any more, as it has been(Purslow, 1999).Looking across12 beefmuscles,a small correlationbetweentheamount of collagen andtendernessatÿ0.36wasseenbut within eachmuscle therewas nosignificant correlation(McKeith etal., 1985)andothersalsofind only aweak correlation between the amount of collagen or the degree of cross-linking and tenderness(Zgubic et al., 1998).Thedifferences in tendernessaccording to age or feeding strategymight therefore be dueto othervariations aswell. A morphological analysis has demonstratedthat the architectureof the intramuscular connective tissue in semitendinosus was dominated by thick collagen fibrils with parallel alignment, tightly bundledinto fibres running in variousdirections.Thefibresformeda tight network,which maypredisposefor tough meat. A characteristicfeaturefor psoasmajor was thin collagen fibrils more randomly distributed forming a criss-cross pattern (Eggenet al., 2001). Theaspectsof organisationof thecollagen fibrils might thereforeexplainsome of thedifferencesbetweenmuscles in tendernessratherthanthedegreeof cross- linking. The useof collagen contentor degree of cross-linking as a raw meat quality markermight thereforebereasonable to somedegreeacrossmuscles,but within a muscle it might be moreopento discussion. 8.3.3 Sarcomere length The sarcomerelengthof the meatdependson the chilling andthe metabolism post-mortem.If the temperatureof a muscle is below approximately10ºC beforetheonsetof rigor mortiscoldshorteningcanoccur.Also stretchingof the muscle before rigor mortis influences the sarcomere length and longer sarcomerelengthshavebeenfound in semitendinosusandbicepsfemorisusing pelvic suspensioncomparedto achillessuspension(Møller et al., 1987).The

sarcomerelength hasbeenshown in beef to correlatenegativelyto Warner- Bratzlershearforce(Toscasetal. 1999).In astudyacrossmusclesin pork it has beenshownthat a sarcomerelength above2m always implies tendermeat whereasotherfactorsinfluencethetendernessat lower sarcomerelengths.This couldexplainwhy somemuscleslike semitendinosusarenot astoughasmight have been expectedfrom the collagen content (Wheeler et al., 2000). The sarcomerelength can be analysedby laser diffraction. It is important to do severaldeterminationson thesamemuscleasthesarcomerelengthnot only on Quality indicatorsfor raw meat 163 differentslicesfrom thesamemuscle,butalsoonseveralsiteson thesameslice (Honikel et al., 1986). 8.3.4 Enzymatic activity It has long been known that ageing the meat increasesthe tenderness. The optimal length of ageing depends on the species– pork having a shorter recommended ageing time than beef. During the ageing period the protein structuresaredegradedbeginning with a diffusion of the Z-lines. Two enzyme systems are said to be involved in this tenderisation – the calpains and the cathepsins.Theexactroleof thetwo enzymesystemsduringtenderisation is still a matterof discussion(O’Halloran et al., 1997). The calpainsare nonlysosomale enzymes. Betweentwo and four different calpainsaredescribeddepending onspecies(Dransfield, 1999).In beefandpork -calpain and m-calpain are expressed in the meat cell. The -calpain is activatedby M concentrationof Ca2+ comparedto m-calpain that is activated by mM concentrationsof Ca2+. -Calpain and not m-calpain is said to be the most important enzymeduring the tenderisation process (O’Halloran et al., 1997; Dransfield, 1999; Geesink and Koohmaraie, 1999) even though many questions still remain (Dransfield, 1999). The activity of the calpains during ageing depends on the concentration of Ca2+, on the pH, and on the concen- tration of their inhibitor calpastatin (O’Halloranet al., 1997).The proportion of -calpainto calpastatin hasbeenshown to explain morethan50%of thechange in myofibrillar fragmentation index during conditioning but only 30% of the changein shearforce during the same period(McDonaghandOddy,1997). Thecathepsinsarelysosomalenzymeswith a low pH optimum– between 2.0 and 6.5 (Ertbjerg, 1996). As the pH of the meat decreases post mortem the membraneof the lysosomesbecomesleakyandtheenzymesarereleased.Even though most focushasbeenon -calpain other investigations haveshownthat the cathepsins alsomight contributeto tenderisation especially whenthe pH of the meat hasdropped (Ertbjerg, 1996;O’Halloranet al., 1997). The activity of the proteolytic enzymesat slaughter dependson the growth rateprior to slaughter.A highmuscleproteinsynthesispre-slaughterandthereby a high activity of the proteolytic enzymesin vivo could imply a fasterrate of protein degradationpost-mortem.This hypothesishasnot yet beenconfirmedor rejected (Therkildsen, 1999).However, recentstudiesin pork indicatethat this relationshipexistsandtherefore the activity of -calpain prior to slaughter is a raw meatquality indicator for tenderness(Therkildsenet al., 2002). 8.3.5 pH and water-holding capacity pH is an important raw meat quality indicator with respect to technological quality and influences the fresh meat eating quality as well. A quadratic connection betweenpH andtendernessandjuicinesshasbeendescribed in both pork (Dransfield et al., 1985) and beef (Cummings et al., 1999) but the main 164 Meat processing connection in both experimentsoccurred when pH was above6.0. In normal meat– pH below 6.0 – therewas no influenceof pH on either tenderness or juiciness. This wasconfirmedin a recent experiment finding that eventhough meatwith a pH below 5.4hada higherdrip lossthanmeat with pH between 5.4 and5.8 therewasno differencein juiciness(Aaslynget al., 2002). Even in the normal pH rangean effect on flavour can be expected. The beef flavour in a steakcookedto 60ºC (rare) was significantly higher when pH was below 5.6 compared to a pH above5.6. This is dueto the fact that the Maillard reaction, which is responsiblefor many of the flavour componentsis very dependent on the pH (Tressl et al., 1989; Farmer andMottram, 1990;Meynier andMottram, 1995;MadrugaandMottram, 1995). 8.3.6 Colour Colour is an importantraw meat quality attribute asit influencesthe consumer in the choice of meat. A too pale or too dark colour often meansthat the consumerrejects the meat. The colour of fresh meat is a combination of the reflection due to protein denaturation as a result of the pH changeand the concentration and oxidative status of myoglobin. A fast pH fall early post- mortem results in a palecolourwhereas a high ultimate pH resultsin a dark,red colour. Myoglobin is purple but oxidation to oxymyoglobin gives a more red colour that for many consumers indicates freshness. During storage the oxymyoglobin can further oxidise to metmyoglobin, which causesa brown discolouring (Gutzke et al., 1997).Therateof oxidation depends on thespecies (Gutzke et al., 1997). The colour of raw meatcanbe determinedinstrumentally or visually (Hunt, 1991).In an instrumentaldetermination thevaluesa*, b* andL* aremeasured. Fromthese variousother characteristics canbecalculatedlike Hueangle,which is usedfor distinguishingcolour familiesandchroma,which is thestrength of a colour. a* represents the rednessof the meat and is very dependent on the blooming time (Hunt, 1991). It is influencedby the pH of the meat because oxidation and reduction processes of myoglobin are pH-dependent. In comparison L* is independent of blooming time but still very dependent on pH (Breweret al., 2001b).As about65%of thevariationin L* canbeexplained from variations in solubility of thesarcoplasmaticproteins(Jooet al., 1999)L* is a goodindicatorof degreeof PSE/DFD (Breweret al., 2001b). A visual determination of meat colour must be standardised using only trainedassessors. Variousscaleshavebeenuseddepending on the speciesand on theexactpurposeof thestudy (Hunt,1991).In pork a much-usedscaleis the Japancolour scale whereasvarious scalescan be used in beef. In general standards like photos are very helpful both in calibrating the assessors and in ensuringthat the scaledoesnot drift with time. Quality indicatorsfor raw meat 165 8.4 Determining eating quality The eatingquality of meatcanbedeterminedbothsensorily andinstrumentally. In a consumertest,where consumers areaskedif they like or dislike the meat sample, the hedonic quality is described. For a more analytical assessmenta trained sensory panelcanbe used.A descriptive analysis– a profiling – canbe performed in different ways but in general, attributes are described quantitatively asking the question ‘How intensive is this attribute in this sample?’. The attributescoverappearance,texture andflavour. By training the assessorsit is possible to do this analysis objectively (Murray et al., 2001). As meat is normally eaten warm the meat in a sensoryprofiling is served heated aswell. This presents a challengeto the sensory laboratoryasthe meat samplespresentedto all assessors mustreach thesameendpointtemperatureat the same time and be served in a very standardised way. Furthermore, a biological variationcanbe found in texturenot only between two slicesof the same muscle but evenwithin a singleslice of the muscle. This emphasisesthe importanceof very standardised proceduresfor slicing andserving of the meat. In a sensory profile appearance, texture and flavour are determined simultaneously on thesame sliceof meat.This is not possiblein aninstrumental analysis.Texture canbedeterminedby a shearforceanalysis.A meat sampleis cookedin a standardisedway andthenecessaryforce requiredto cut themeatto agiven extentis registered.Diff erenttypesof knivesaswell asdifferentwaysof cutting the meat, e.g. until 80% compression,can be used.The correlation between a shear force analysis and tendernessassessedby a sensory panel depends both on the experimental conditions during the shearforce analysis (TornbergandGöransson,1994;Tornberg, 1996)andon thecooking procedure usedfor the meatfor the sensory panel(Aaslynget al., 2001). Flavour can be determined by GC-MS or GC-O analysis. In a GC-MS analysis the composition of volatile components in the meat headspace is identified andquantified. To translatethis knowledge to anunderstanding of the flavour requires that somekey component of the flavour be known. As meat flavour is a complex mix of manycomponentsthis is rather difficul t. In a GC-O analysisanassessorsniffs at theeffluentof theGC andregisterswhenanodour is apparent. In this way the most flavourpotentcomponents canbe picked out facilitating the interpretation of the GC-MS data(Grosch, 2001). 8.5 Sampling procedure The analysis of a raw meat indicator in a sample is often usedto predict the status of the whole muscle or evenof the whole carcass. There is however a variation bothwithin a muscle, between musclesandbetween animalsandcare must be takenin a prediction from oneanalysis.Figure8.1 showstwo slicesof LD of beeffrom two different animals.The first slice is from the 11th thoracic vertebra. At this position the amount of fat marbling is very different between 166 Meat processing the two animals.The second slice is from the 13th thoracic vertebraonly 8 cm awayfrom thefirst slice.At thisposition thedifferencebetweenthetwo animals is much smaller. If the differencebetween the two animalsin fat marbling was determined from only onesamplethe answer would very much dependon the samplingsite. The effect of samplingsite when determining drip loss in pork has been investigated.On theleft loin thedrip losswasdeterminedusingtheEZ-drip loss methodwhere between one and threecylindrical cuts,25mm in diameter and 25mmthick wereused.The right loin (LD) wasslicedaswell andthedrip loss wasdetermined on the whole slicesusing the bagmethodto simulate the drip lossseenwhena butcheris slicing the loin for sale.The results showed that a correlation between one EZ-drip loss determination and the whole drip of the otherloin was0.9.In this caseonedrip losssampleof LD wasrepresentativefor the whole muscle(Christensen, 2002). Looking acrossmuscles it is evenmoredifficult to predict the meatquality from one sampleof one muscle. LD is often used as the sampling muscle becauseit is of economic importanceandbecauseit is a long muscle andeasyto sample. The variation in tendernessof beef assessedby a sensory panel is however larger in LD than in four other muscles (Wheeler et al., 2000). Furthermore,therelationshipbetween LD andothermuscles in tendernessis not constant(Wheeleret al., 2000)– and for some muscles the correlation is very Fig. 8.1 Fatmarblingin two slicesfrom two differentbeefs.(a) animal1, 11ththoracic vertebra,(b) animal2, 11th thoracicvertebra,(c) animal1, 13th thoracicvertebra,(d) animal2, 13th thoracicvertebra(from N. T. Madsen,DanishMeat ResearchInstitute). Quality indicatorsfor raw meat 167 low (Matthews et al., 1998).TheLD muscle thereforecannotbeusedto predict the tendernessof other muscles.Whendeciding wherea sample for ananalysis is taken, it is therefore very important to considerwhat is the aim of the sampling andnot to conclude more thanactuallypossiblefrom this sample. 8.6 Future trends The future demandson raw meatquality reflect the useof the meat.Two key wordsexist: ‘uniformity’ and‘variety’. A future trendis thedemandfor a large amount of meatwith a uniform raw meat quality for further processing. This makes it important that the raw meat quality can be predictedor determined early– if possible beforethechill ing begins.Anotherfuture trendis thedemand for a greater variety in smaller

amounts especiall y for the fresh meat consumption market. This makes it important that the raw meat quality can be controlled in order to designa specificquality. 8.7 References AASLYNG, M. D., BEJERHOLM, C. and MØLLER, S. (2001). Correlation between shearforceandsensoryanalysis in meatdepending on cooking method. In A SenseOdyssey,Conference Program Abstracts. The 4th Pangborn Sensory ScienceSymposium Dijon, France, p. 240. AASLYNG, M. D., BEJERHOLM, C., ERTBJERG,P., BERTRAM, H. C. andANDERSEN, H. (2002). Cooking lossandjuicinessof pork in relationto raw meatquality andcookingprocedure. Food Quality and Preferences, Accepted. ANDERSEN,H., BERTELSEN, G., BOEGH-SOERENSEN,L., SHEK,C. K. andSKIBSTED, L. (1988). Effect of light and packageconditions on the colour stability of slicedham. Meat Science,22, 283–292. ANDERSSON,M., OLSEN,E. V. andFROESTRUP, A.-B. (1997).Relationship between raw material quality andproduction yield of cookedhams manufactured without the use of phosphates. 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A rancidity andstorability of homemade dry sausageand dry hamandpublic taste of dry ham.KoreanJ. Food Sci.Technol., 15, 6– 11. ZGUBIC, E., CEPIN,S. andZGUR,S. (1998).Correlation betweencollagen traitsand sensorial and physical traits in M. Longissimusdorsi of brown bulls. In 44th International Congress of Meat Science and Technology. Meat consumption and culture, Barcelona, Spain, pp. 768–769. 8.8 Acknowledgement I would like to thankHanneBangBligaard,MarchenHviid, andSusanneStøier for valuable discussionsduringthepreparationof this chapter.Christel Dall and IngeBoje Brun arethankedaswell for alwaysgettingmetheliterature I needed no matterwhenor from where. 174 Meat processing 9.1 Introduction The science of sensory analysis is relatively young when compared with the traditional sciences such as physics and chemistry. An early systematic sensory test was the triangular test (circa 1940) which was used in Scandinavian countries. Parallel development was also in progress in the USA at about this time. The first book on sensory analysis was written by Tilgner1 in Polish and this text was later translated into Czech, Hungarian and Russian. The second book on sensory analysis was written in Japanese (Masuyama and Miura),2 whilst the third textbook, which most sensory analysts will recognise, was that published by Amerine, Pangborn and Roessler.3 This book was based on the lectures given at The University of California at Davis as part of their Food Science course programme. A very practical book by Jellinek4 is useful for teaching, and contains what are in effect menus of how to set up basic training courses as an introduction to sensory analysis. More recent books such as that by Meilgaard, Civille and Carr5 build upon previous works and include applications of difference tests that have been developed in the intervening period. Sensory analysis is very much an interdisciplinary subject and the aforementioned works cover in some detail the basis of human sensory perception related to thresholds of determination of basic tastes, the variance in individual sensory response and some examples of experimental design. The importance of good experimental design cannot be overemphasised in sensory experiments. Two useful texts are those published by Cochran and Cox,6 a general statistics book on experimental design, and that by Gacula, Jr and Singh,7 a statistics book aimed more specifically at sensory analysts. Many of the procedures used in sensory analysis are applicable to many different food 9 Sensory analysis of meat G. R. Nute, University of Bristol items, including meat. This chapter will outline the methods used in the recruitmentof sensory assessors,types of panelandtraining relatedspecifically to meatandwherepossible publishedexamplesof wherethe different typesof tests havebeenusedin meatresearch. 9.2 The sensorypanel As far asthe sensory analyst is concerned, sensory assessorsareeffectively the instrumentsusedto determinethesensoryattributesof a food item.Thefirst step in sensoryanalysisis to assemblea panel. Thereis theoptionof using members of staff if therearesufficient numbersavailable. If this option is chosen, it will benecessaryto impressuponlinemanagersandindividuals thatit is anessential partof their dutiesto attendpanelsessions. Thedisadvantageof this approachis that, whilst a considerableamount of time andeffort is devoted to timetabling the sessions to ensureeveryoneis available, therecanstill be problems of non- attendance at panels.This raisesthe issueof missing data which is a major problem in meat tastingif it hastaken up to two yearsto produce an animal. Thereis alsotherelatedproblemof pre-conditioning thepanel.Thiscanoccurin small companiesandresearch groupswherethe assessorshavea good ideaof what the researcher is working on. An alternative to the in-housepanelis the recruitmentof an external panel. Thesepeoplearepaid to attendsessionsandoftenreceive a bonusto encourage full attendance. The advantages and disadvantagesof this type of panelhave beenaddressedby Nally8 who describeshow theyoperate andtheir costs.Some of thesectionson termsandconditionsof employmentgivenin herpaperdo not apply in the Euro zone.The advantageof this type of panelis that the sensory analyst cantakemoretime to train thepanel,andhold discussionsfor profiling without having to curtail sessions because assessors have other work commitments.The assessors are relaxedbecause their job is solely to attend the panelsessions. The disadvantageof this type of panelis the initial effort in advertising and setting up screening sessions for potential assessorsand the further training that occurswith meat.When assessors leavethere is often no quick way of recruiting assessors unlessa reservelist of pre-screenedassessors is kept and it remainsavailable. 9.2.1 Screeningcriteria and training Potential sensory assessorsare required to undergo a seriesof screening tests. Theseprocedures have beendocumentedby various standards organisations, notably The Bri tish Standards Insti tution (BSI), The International Standardisation Organisation (ISO) and The American Society for Testing Materials (ASTM). All these organisations publish methodsfor selectingand training sensory assessorsand give detailsof how to establish the basic taste acuity of assessors. As an example, assessors canbe screenedaccording to the 176 Meat processing methodsoutlined in the relevant BSI standard: BS 7667,Part1.9 This Standard outlines the methodsof assessingan individual’s ability to taste,assessand describe odours, assessand describe textures.Theseprocedures will highlight any

individualsthat are unlikely to be efficient sensory assessors. When these testshavebeencompleted it will be necessary to start training with meat.The methodsoutlined by Cross et al.10 for basic training in meat are useful in training assessors. Their methodsare basedon utilising research results that showvariations in sensory attributes.However, with the adventof BSE in the UK, it is no longer possible to usesteaksfrom animals over30 monthsof ageas examples, and consequently it has been necessary to modify some of their suggested materials andmethods. 9.2.2 Using samplesin training It is particularly importantto preparesamples carefully when training assessors and assessing consistencyof performance. A useful procedure for producing rangesof texture, juicinessand flavour in pork, for example, is to follow the methodsoutlinedby WoodandNute.11 Theproceduresarebasedon varyingthe endpoint cookingtemperatureof pork steaks.Threeendpointtemperatureswere used:65ºC,72.5ºCand80ºC.Thesteaks(1.90cm) werecut in triplicate to create a seriesof uniform samples,an importantaspectin reducingvariation. Eight- point category scaleswereusedfor texture, juicinessandflavour where: 1ˆ extremely tough,extremely dry, extremely weak 2ˆ very tough, very dry, very weak 3ˆmoderately tough,moderately dry, moderately weak 4ˆ slightly tough, slightly dry, slightly weak 5ˆ slightly tender,slightly juicy, slightly strong 6ˆmoderately tender,moderately juicy, moderatelystrong 7ˆ very tender, very juicy, very strong 8ˆ extremely tender,extremely juicy, extremelystrong Analysis of variances revealedhighly significant (p< 0:001) differences in texture related to endpoint temperature.Therewere means of 5.1, 4.5, 4.2 for 65ºC,72.5ºCand80ºC respectively, with a standarderror of the differences of means(s.e.d)of 0.153.Means for juicinesswere5.0, 4.3, 3.5 at 65ºC, 72.5ºC, 80ºCrespectively. Meansfor pork flavour intensitywere3.4, 3.5, 4.1 at 65ºC, 72.5ºCand80ºC respectively. This approachwastestedusingdifferent sources of pigs andwasfound to be consistentin all cases. Theassessmentof beefusesprocedures basedon modifying theconditioning period.To produceanexampleof extremetoughness,it is necessary to removea section of hot m.longissimusdorsi, vacuumpackand immediately plungeinto iced water, followed by blast freezing at ÿ40ºC. To producetender beef, it is necessary to vacuumpack a section of m.longissimusdorsi and condition at +1ºC for 20 days.Extremely tender beef can be produced by using m.psoas major, vacuumpacking andconditioning for 10 daysat +1ºC.Dransfield,12 has Sensory analysis of meat 177 publisheda study in which instrumental toughnesswas measured in 18 beef musclesandheatedin a waterbathto 60ºC,75ºCand90ºC. Theseresultscanbe usedto produce further examplesof toughnesswhen training assessors. 9.2.3 General conditions for the assessment of samples To conduct effectivesensory panels,assessorsneedto befreeof distractionsand the tests should be carriedout in a specialroom in which there is controlled lighting andgoodventilation. Assessorsshouldbeseatedat separate booths and should not be able to communicate with eachother during the assessments. Samples of food should be uniform in size and of the sametemperature at serving. Theyshould becodedby a randomthree-digitnumber andpresentedin cleanodour-freecontainers.If morethanonesampleis to beassessed, thencare is neededto ensurethat the assessors do not receivethe samplesin the same order, since this will introduce a bias. Assessorsare instructed to rinse their mouthsout with waterbetween eachsampleto removeall tracesof theprevious sample. 9.3 Sensorytests Therearea rangeof different typesof test: • differencetests • pairedcomparisontests • triangular tests • alternative forcedchoice/3-AFC tests • duo-trio tests • ‘A’-‘ not A’ test • ranking tests • two from five test. 9.3.1 Difference tests Diff erencetests aretests where theassessoris presentedwith a choicesituation, i.e., askedto select the odd sample or match the sampleto a referencefor example. A generalconsideration when using difference tests for meat is to understandthevariancesthatoccurnaturallyin meatandthecomplications that arisein the interpretationof the results.It is importantnot to biasthe test.This means that,when presenting samples,it is necessary to ensurethat the samples areat thesametemperature,cut thesamesize,presentedin thesame way and,if colour differences arepresent, presentthesamples underredlight to mask these effects. 178 Meat processing 9.3.2 Paired comparison tests(BS5929:part2:1982,ISO 5495)13 The paired comparison test is used to determine differences or preferences between two samples for a specified attribute, e.g., tougher or more tender. Thesedifferencesmaybedirectional or non-directional.A typical question in a directional test would be: ‘Which sampleis more tender?’. Here the method requires at leastsevenexperts or 20 selectedassessors. A typical questionfor a non-directional test would be: ‘Which of these two meat samples do you prefer?’ . Directional tests are one-sided (one-tailed tests) whereas non- directional testsare two-sided (two-tailed tests).It is necessary to balance the orderof presentationof samplesA andB asshown in Table9.1.SincetheBSI/ ISO standard was published, further work on the operationof the test was published by Thiemeand O’Mahony,14 They suggested that if assessors were exposed to the rangeof sampleslikely to be encounteredin the test, then the warmed-uppairedcomparisonwasthemostsensitive test compared to theduo- trio and ‘A’ ‘not A’ test. An investigation into the influenceof a decontaminationmethodusinglactic acidon broilers wasconductedby Van derMarel.15 Broilersweresubmergedin 1% (v/v) lactic acid for 15s, pH 2.4, 15ºC at three stagesduring processing. Carcasseswere then stored for two days after which samplesof thigh and drumstick were removedand then grilled for 30 minutes.Control and treated samples were presentedas a pair to eachassessor (12 assessors took part, 4 pairedcomparisons each)who were askedwhich samplethey preferred.This application (pooling replicate results) of the paired comparison was a non- directional test and the expectednumber of choices in a particular direction would be32/48. In this casetherewere26 responsesin thecontroldirectionand 22 in the treated direction. The assumption is that using lactic acid as a decontaminant would not be detectedby a trainedpanel. Table 9.1 Presentationof samplesin directionalandnon-directionalpreferencetests Directional test Non-directional Preferencetest Assessor Presentationorder Presentationorder Set1 Set2 Set1 Set2 1 AB BA AB AA 2 BA BA BB BA 3 BA AB BA AB 4 AB AB AB BA 5 BA AB AA BB 6 AB BA BB AA 7 AB AB AB BB 8 BA BA AA AB 9 BA AB BB AB 10 BA BA AA BA Sensory analysis of meat 179 9.3.3 Triangular tests(BS5929:part3:1984, ISO 4120-1983)16 In triangular tests, threecodedsamplesarepresentedsimultaneously, of which two are the same and one is different. Assessors are askedto selectthe odd sample. Al l six combinations are served (ABB,AAB,ABA,BAA,BBA,BAB). Some assessorswill receive two samplesof A andoneof B, whilst otherswill receive two samplesof B and one of A. If the number of assessorsis not a multiple of six then it is necessaryto presentthe six setsto eachassessoron several occasions.Theprobability of selecting thecorrectoddsampleby chance alone is 1/3. To analyse the test results, the number of correct replies at the agreed level of probability is comparedwith those in the referencetable and checked to see if the number of correct replies exceedsthat in the table of probability where pˆ 1/3. If the number is exceeded than the samplesare significantly different. In testson meat it is usually not sufficient to assumethat the difference between a pair of treatmentswill beconsistentacrossall animalsandtreatments andusuallythe testis repeated usingdifferentpairsof animals.The question of whether it is permissible to combine the results of triangular testshas been discussedby Kunert and Meyners,17 who stated that, if the experiment was properly randomisedandcontrolled, then the assessments are independent and have a successprobability of pˆ 1/3. Therefore, the sum of all correct judgements is binomial and the parameter pˆ 1/3 applies. This fulfils the criteria for the null hypothesis where A ˆ B, i.e., no difference across n replications. DacremontandSauvageot18 havereported that, in some specific areas,it is good methodological practice to apply replications in triangular tests. This approachwasappliedby Dransfieldet al.19 in a studyof bull versussteermeat. In anattemptto reducevariationbetween animals,pairsof twin bulls (dizygous) wereobtainedandoneof the pair castratedat 80 days.Four different cooking procedures were used: roasting, casserole, mince and gri l l ing using m.longissimus dorsi, m.supraspinatus, m.gastrocnemius and m.psoas major respectively. The results showed that bull meat could be significantly distinguishedfrom steermeat. Later work by Dransfield et al.20 on twin lambs from two different breeds,Dorset Down and Suffolk crosses,and comparing entires andcastrates,showedthat52/106assessmentsdifferentiatedthesexesin the DorsetDown comparisonand49/110in Suffolk crosses.Both resultswere significant (p< 0.001). In trials on lamb from the same experiment, but unpaired andusingstandard attribute tasting,no significant differencebetween ram and castrate lamb was observed. The inference is that, in the highly controlled twin situation, there is some difference that enabledassessorsto identify ram from castrate, but this differencecould not be established in the unrelatedlamb system often encountered in sensorytesting.It is important to rememberthat thetriangular test is usedfor differenceonly, it is not permissible to askassessors to identify the ‘odd’ sampleon somecriteria, e.g., flavour. 180 Meat processing 9.3.4 Alter native forced choice,3 – AFC21 This test is similar in theway samples arepresentedto thatof thetriangular test with oneimportantdifference:the ‘odd’ sample is alwaysthe samethroughout the test.The probability of selecting the ‘odd’ sampleis still pˆ 1/3. This test hasapplicationsfor estimatingthe sensory thresholdof individualsandgroups of assessors.This approach hasbeensuccessfully utilised in studies on ‘Boar taint’ by Annor-Fremponget al.22 incorporating theascending methodof limit s methodin conjunctionwith 3-AFC. Using a model system in which individual samples of androstenoneandskatolewereusedin a neutrallipid base,assessors wereaskedto sniff thesamplesandindicatethe‘odd’ sample.Theconcentration on subsequent testswas gradually increased in the ‘odd’ sampleuntil it was detected.This approachwassuccessful in showing how individual responsesto androstenoneandskatolevaried.It alsoenabledagroupthreshold responseto be established,effectively the sensitivity thresholdof the panelasa whole. The range of sensitivity of individual assessors varied from 0.018 to 0.143ggÿ1 for skatole with a group threshold of 0.026ggÿ1, and 0.250 to 1.000ggÿ1 for androstenonewith a group estimate of 0.426ggÿ1. In both series of trials, two different individuals had very low thresholds for androstenoneand skatoleand were excluded from further trials. Inclusion of thesesuper-sensitive individualswould influenceany paneltest for usingthese compounds. Including non-sensitive assessorsin a panel just to make up the numbersalsopresentsa problem.Thesesituations highlight the needto screen assessors beforecommencinga

sensorytrial, particularly whenthe responseto an individual threshold for a compoundis unknown. 9.3.5 Duo-trio test (BS5929:Part 8:1992; ISO 10399,1991)23 The duo-trio test is an intermediate betweenthe duo (paired) and the trio (triangular) test andis statistically lesspowerful thanthetriangle test. In this test the assessorreceives one samplemarkedas a reference sample and two other codedsamples and areaskedwhich of the two samplesmatches the reference sample. The probability of selectingthe correctsampleby chance is 1/2. The presentation order for the duo-trio test is shownin Table9.2. Studieson the influenceof chill ing method,eitherwateror brine chilled, on theeating quality of chickenbreastandthigh meatswereinvestigatedby Jankey and Salman.24 They usedthe duo-trio approachand gavebetween 20 and 25 assessorssamplesof deepfried chickenpieces.Assessorswereableto detectthe difference between chicken piecesfrom the two chill ing treatmentsin both breastand thigh meats.Instrumental sheartestsdid not reveal this difference, althoughit was thought that textural differenceswould be the likely outcome from the chill ing treatments. 9.3.6 ‘A’-‘n ot A’ test (BS5929:part5:1988)25 This testis usedfor evaluating sampleshavingvariationsin appearance (whenit is diffi cult to obtain strictly identical repeatsamples).It canbe alsousedasa Sensory analysis of meat 181 perception test, to determine the sensitivity of an assessorto a stimulus. Assessorsare askedto look, smell, touch or taste sampleA and remember everything aboutthe sample. The sample is thenremovedandreplacedwith a number of samples,(in some US textbooks, both ‘A’ and ’not A’ samples are presented).The numbersof ‘A’ and‘not A’ samples presented areunknown as far astheassessoris concerned.However, it is convenient to balancethenumber of ‘A’ and‘not A’ samplessothat,instead of calculating thechi-square,pˆ 1/2 tablescanbeusedto investigatedifferences.However, it is importantto addthe number of correct resultswhen ‘A ’ is recognised to the number of the correct results for ‘not A’. It is thetotal numberof correctresponsescheckedagainstthe total number of responsesthat areusedwhenusing pˆ 1/2 tables. Table 9.2 Presentationorder for the duo-trio test Constantreferencetechnique SampleA is the referencesample Presentationorder Assessor Set1 Set2 1 R AB R BA 2 R BA R BA 3 R AB R AB 4 R BA R AB 5 R AB R AB 6 R BA R AB 7 R AB R BA 8 R BA R BA 9 R AB R AB 10 R BA R AB 11 R AB R BA 12 R BA R BA Balancedreferencetechnique* Presentationorder Assessor Set1 Set2 1 RA AB RB AB 2 RA BA RB BA 3 RA AB RB AB 4 RA BA RB BA 5 RA AB RB AB 6 RB BA RA BA 7 RB AB RA AB 8 RB BA RA BA 9 RB AB RA AB 10 RB BA RA BA 12 RB BA RA BA * Sometimesreferredto asthe ‘alternatingreferencetechnique’. 182 Meat processing If using the chi-squared test approach then the results from the test are recordedfor eachsample andusedto construct a 2 2 contingencytable.The number of correctandincorrectresponsesdetermine whether ‘A ’ is recognised in a different way to ‘not A’ . Considerwhen a particular ingredientis usedin a meatproductand,for commercialreasons,it is necessaryto changesuppliers of this ingredient. The manufacturer wishes to know whether the replacement ingredient canbe identified from the original. Twenty assessorstakepart in the testandaregiven five samplesof ‘A’ andfive samples of ‘Not A’. Theorderof presentation is given below: Assessor Sample presentation order 1 to 5 A A B B A B A B B A 6 to 10 B A B A A B A A B B 11 to 15 A B A B B A B B A A 16 to 20 B B A A B A B A A B Havingcompletedthetest,theresultsareassembledinto a22 contingencytable: Sampleidentified as Samplepresented Total ‘A’ ‘Not A’ ‘A’ 60 35 95 ‘Not A’ 40 65 105 Total 100 100 200 The chi-squared index is calculated using the expression: X2 ˆ X i;j ; …Eoÿ Et†2 Et whereEo is theobservednumber in box i,j (in which i is thenumber of therow andj is thenumber of thecolumn); Et is thetheoreticalnumberin thesame box given by the ratio of the product of the numberfrom the row and the number from the columnto the total number. In this casethe X2 index is 12.53 andthe critical value 3.84at 5% probability. Therefore in this casethereis a significant differencebetweenthe original ingredientandthe replacement. 9.3.7 Ranking tests (BS5929:part 6 1989: ISO 8587:1988)26 Ranking tests are concerned with putting samples in order according to the strengthof stimulusperceived.Ranking testshavetheadvantagethatmore than two samples canbe comparedat the sametime, whereasonly two samplescan be compared in difference tests. However, the disadvantage is that inexact results can be obtained if the differences are very small or the samples themselves havewide variationsbetween them.In this test, assessorsarelikely to suffer from sensoryfatigueandthis limit s theusefulnessof this testfor meat. Assessors evaluatea numberof samples in random order and are askedto place them in rank order based upon a specified criterion. Assessors are Sensory analysis of meat 183 instructed to avoid tied rankings wherepossible. Results are then collatedand theranksumsfor individualsamplescalculated.Foranoverallcomparisonof all the samplesthe FriedmanvalueF is calculatedusingthe following formula: F ˆ 12 JP…P‡ 1† …R 21‡ R22‡ R2P† ÿ 3J…P‡ 1† where J is the number of assessors,P is the numberof samples,andR1, R2 are theranksumsgivento P samplesfor J assessors.If F is equalor greaterthanthe critical value corresponding to the number of assessors, the numberof samples andtheselectedlevel of significance,it canbeconcludedthat thereis anoverall differencebetween the samples. If anoverall differencehasbeenestablishedbetweensamples, theranksums of each samplecan be used to identify the significant differences between sample pairs as follows. Let i and j be the sampleswith Ri and Rj their rank sums. Using the normalapproximation, the two samples aredifferent if: jRi ÿ Rj j 1:960 JP…P‡ 1†p 6 for 5% level of probability Despite theproblemof sensory fatiguetherearestill opportunitiesto useranking tests in the meat area.Sheard et al.27 investigatedthe factors that affect the ‘white exudate’ from cookedbacon.A rangeof 20 photographs were takenof the different levels of exudate from bacon and assessors ranked these photographs in order of increasingexudate. The results revealeddifferences between dry cured, Wiltshire untempered and rapid untempered, Wiltshire temperedandrapid temperedbacon.Thedry cured baconhadthe least exudate and the rapid temperedbaconthe most. A second experiment examining just Wilt shireandrapidcuring methodson loins from the samepig showedthat the Wilt shiremethodhadthe least exudateandthe rapid methodthe most. 9.3.8 Two from five test28 This is a generaldifferencetest which canbe moreefficient statistically thanthe triangular testsincetheprobabilityof correctly guessingthetwo oddsamplesis 1/10 comparedto the triangular test andpairedcomparisonwhich are 1/3 and 1/2 respectively. Unfortunately thetwo from five testcanbeaffectedby sensory fatigue and this should be taken into consideration before this procedure is selected.Thetestconsists of presenting assessors with five sampleswherethree of the samples areA andtwo areB or threeareA andtwo areB. Thereare20 possible combinations of two from five samplesasshownbelow: AAA BB ABABA BBBAA BABAB AABAB BAABA BBABA ABBAB ABAAB ABBAA BABBA BAABB BAAAB BABAA ABBBA ABABB AABBA BBAAA BBAAB AABBB 184 Meat processing If thenumberof assessorsarelessthantwenty it is importantto selectat random from the above combinations, ensuring that there are an equal number of combinations that contain three As and three Bs. However, it has not been possible to find any applications of this testbeing usedin meatscience. 9.4 Category scales Category scalesareoftenusedto ratea numberof differentstimuli, e.g.,texture, flavour andjuiciness.Theyhavetheadvantagethat theyareeasyto useandcan covera number of attributes,aswell asup to six samples in a session. For the test to be successful it is necessary to have good experimental design.The resultscanthenbeanalysed,for example, usinganalysisof variance techniques to establishthe differencesbetween and within the samples. The useof these typesof category scalesis useful for determining thegrossdifferences in eating quality and is frequently usedin animal productionexperiments that require sensory data. However, this approach may not yield sufficient information if thereis a needto identify the individual characteristics of a food, in which case it is necessaryto derivea profile of thefood.Thereis oftendebateon how many scalepointsshould beusedin a category testandwhether thecategoryapproach is the most efficient in terms of reproducibility and discrimination. Work by Lawless andMalone29 examinedfour typesof rating scales,nine-pointcategory scales,line marking,magnitudeestimationanda hybrid category andline scale. Theyshowedthat all methodswereableto find significant differences between products. However, category scaleshad a small advantageover the other methods. The term ‘rating’ hasbeenintroducedasagainst‘scoring’. Thesetermsare often interchangedin sensory experiments on meat, but there are important differences between the two terms. Lawlessand Malone30 compared ratings scales for their sensitivity, replication and relative measurements. They concludedthat that in spiteof thesmall physical differences within thesamples givento assessors,assessorsusedwide rangeswithin thescales.This conclusion supports the view that rating scalesare relative. The term ‘scoring’ hasoften beenusedin sensory analysisof meatbecausemuchwork on meat hasinvolved carcassgradingandjudging. In thesescenarios it hasbeenpossible to produce photographicstandardsdepicting thevariousdifferencesbetweenthecategories andthenallocate a score. In meat tastingthis is very diffi cult to achievebecause of the difficulty of reproducing examples of meat at each scale point in a category scale. Thereis a furtheraspectto consideron whetherassessorsareaskedto rateor score a sample and this concerns the relationship between a physical measurement produced by an instrument and a psychological or sensory impressiongiven by an assessor.An instrument that gavedifferent values on different days for the same measurement would be quickly disregarded or repaired. Treatinga sensorypanelas an instrument of measurementhasat its Sensory analysis of meat 185 heart a belief that a particular point on a scaleof physicalmeasurementwill alwaysbe associated with a physical stimulus in an assessor.31 Psychological impressionsdependon a number of factors related to the other samples present in the testandthestimulusthat theygeneratein theassessor. They alsodepend on theintensityof thestimulusnot reaching thepoint whereresponseadaptation occurs i.e., the point at which an increasingintensity of the stimulus doesnot evokean impressionof increasing responsesin the assessor.32 In meat scienceexperiments,where the interest is in the major changes that occur, category scalesare widely usedand thereare many examplesof their application. In a studyon the influence of breed,feedandconditioning time in pork, Wood et al.33 used eight-point category scalesto show that conditioning time affectedthe tendernessof pork, with ten-dayconditioning producingmoretender pork thanone-day conditioning. Pork flavour wasalso increased after ten days and abnormal flavour decreased.Breed effects showedthat Durocs hadmorepork

flavour thanLargeWhites.In a studyby Sheard et al.34 on polyphosphateinjection at 3% and 5% concentration in pork, eightpoint categoryscaleswereusedby a panelof ten assessors to rate tenderness,juiciness,pork flavour intensity and abnormal flavour intensity. The resultsshowedthat tenderness increasedwith increasingconcentration of polyphosphate. Juiciness also increased with concentration to 3%, but increasing concentration beyond 3% did not increase juiciness perception. Pork flavour intensity decreased with increasing concentration of poly- phosphate.The responsesweresimilar in pork from both entires andfemales used in this trial. 9.5 Sensoryprofile methodsand comparisonswith instrumental measurements Therearevariouswaysof carryingout descriptiveanalysis of foods. Thereare two basicmethodsof profiling: fixedchoiceprofiling andfree-choiceprofiling. In the fixed-choicemethod,the assessorseachdevelopa vocabularyto describe the food undertest.Oneof the assessorsactsaspanelleaderandtheir taskis to discussthe words generatedby the other assessorsso that a consensuscan be agreed. Theagreedsetof descriptorsis thenused to describethe food. The free- choice methodinvolves the assessorsbeing given the likely rangeof samples during anumberof trainingsessionsto derive aprofile thatis uniqueto them.The assessorsthenusethis profile to describethe foodsin theexperiment.In bothof these methods,it is importantthat theexperimentsarewell designedstatistically since, if they arenot, it is unlikely that meaningful resultswill be obtained. The relationship between sensory and instrumental results is an area of considerableinterest. Relating the two is particularly importantin suchareasas new productdevelopment. Sensoryanalysis can help set the parametersfor a new formulation, but instrumental measurements are needed to develop and ensure consistent productquality. Nute et al.35 haveexplored the relationship 186 Meat processing between the sensory characteristics of ham and product composition. In this work 52 hamsamples wereobtained andsubjectedto sensory andinstrumental analysis. The hams were subdivided into three groups, traditional, modern tumbled and massagedhams,and cannedhams.A generaldescriptive profile covering appearance, texture and flavour was developed. The study used a methodof statistical analysisknown asGeneralisedProcrustesAnalysis (GPA), originally described by Gower,36 where the methodsof assessors’ usageof scalesare takeninto account in the analysis. Therearebasically threestepsin GPA analysis: 1. Translation. This is a methodof standardising the meanratings for each assessorfor eachattribute. This effectively removesthe variationbetween assessorslocationsalong an adjectival scale. 2. Rotation/reflection. This takes account of assessors’ usageof different adjectives to assess the samesensory stimulus. A good example is the confusion between the terms ‘bitter’ and ‘astringent’ as documented by Langron.37 3. Scaling. The overall variation among samples rated by eachassessor is standardisedandremovestheeffectof assessors ratingover differentranges of the adjectival scales. In this particular experiment all three steps were highly significant and demonstratedtheeffectivenessof GPA asdeterminedby a procrusteananalysis of variance. It should be mentionedthat the calculation of the degreesof freedomis differentfrom anormal ANOVA. With A assessorsandD descriptive adjectives, the degreesof freedomare; D(A-1)for translation, A-1 for scaling andD(A-1)(D-1) for rotation/reflection. Theoverall conclusionshowedthat thefirst principal axisaccountedfor 33% of thetotal variationandwasa contrast between gelatinousappearance andfirm texture. The second principal axis, accounting for 17% of the variation, was relatedto the appearanceandflavour of the productswhilst the third principal axis was related to colour, fatnessand saltiness. Examining the relationship between mechanical andsensorypropertiesshowedthat firmnessincreasedwith shearstrength,and that gelatinousand plastic appearancewas relatedto the amountof boundwater in the hams. In studies on the effectsof fatty acid composition and its effect on eating quality, Fisher et al.38 showedthat the flavour of meatfrom lambscomprising WelshMountain, Soay, Suffolk off grassandSuffolk off concentratescould be characterisedusinga flavour profile. A profile containing 12specific descriptors for flavour and five general descriptors adaptedfrom category scalesand converted to line scaleswasdeveloped.Lambmeatfrom Soaywascharacterised by significantly highervaluesfor ‘livery ‘and ‘fishy’ flavours.Otherdifferences between thelambbreedswererelatedto thedifferencesbetween thoselambson foragesystemscompared with thoseon concentratesystems. Savageet al.39 studied the changesthat occur in adhesion between meat piecesusing different concentrationsof a crude myosin solution. Mechanical Sensory analysis of meat 187 tests hadestablishedthat it waspossible to measure differences in total adhesive strength, butwhat wasrequired wasadescription of howthiswasperceivedby a trained sensory panel. A fixed profile using the descriptors shown in Table9.3 wasdevelopedover a numberof training sessionsusingthe sameassessorson eachoccasion. Usinganalysisof variance with myosin concentrationasa factor, for each individual descriptor, differences that were related to myosin concentration were revealed as summarisedin Table 9.4. Assessorswere able to differentiate differences in adhesion caused by increasing myosin concentration and showed that sampleswith higher levels of myosin were firmer when cutting and lesscrumbly. When eating,higher levels of myosin resulted in samples that were more rubbery, less easy to fragment and less tender. Table 9.3 Line scalesusedin a textureprofile of restructuredbeef steaks(eachline 100mm in length) Descriptor Anchor points Tactile Left point Right point Firmnesson cutting Nil Extreme Crumblinesson cutting Nil Extreme Fibrousparticleson cutting Nil Extreme Eating Rubberiness Non-rubbery Rubbery Easeof fragmentation Cohesive Readilyseparating Degreeof comminution Coarse Fine Tenderness Extremelytough Extremelytender Moistness Dry Wet Table 9.4 Effect of addedmyosinon the sensoryattributesof meatproducts % addedmyosin signf. lsd Sensorypanel 0 1.75 3.5 5.25 7.0 Tactile Firmnesson cutting 50.5 57.5 61.0 64.5 68.7 *** 4.2 Crumblinesson cutting 35.0 17.1 14.1 11.3 8.5 *** 4.1 Fibrousparticleson cutting 26.2 20.4 18.1 18.2 15.6 *** 3.5 Eating Rubberiness 49.3 48.9 53.6 59.4 60.0 *** 4.5 Easeof fragmentation 61.0 55.7 50.6 43.7 43.4 *** 4.2 Degreeof comminution 48.5 50.6 50.6 47.3 49.6 n.s. 4.0 Tenderness 60.4 61.6 60.7 56.4 56.4 ** 3.5 Moistness 50.3 57.9 58.1 58.8 56.1 ** 4.7 lsdˆ leastsignificantdifference;n.s.ˆnot significant. ** ˆ p< 0:01; *** ˆ p< 0:001. 188 Meat processing 9.6 Comparisonsbetweencountries Theuseof sensorypanelsin differentcountriesoftenleadsto theneedto compare resultsacrosscountries.Work hasbeendoneto investigateif resultsachievedwith one panel in one country are the same as in another country. Two early comparisonswerecompletedby Dransfield40 et al. Thefirst experimentcompared meatfrom beefanimalssuppliedby five researchinstitutes.Eachcountrysupplied loin steaksfrom ten animals and eating quality was comparedin Denmark, Ireland,the UK, FranceandGermany.The panelsin eachcountry found a wide variation in eatingquality and many of the steakswere very tough.A common eight-pointcategoryscalewasusedfor tenderness/toughness.Betweenthepanels tendernesswashighly correlatedwhilst flavour andjuicinesswerepoorly related. Theconcernin this experimentcentredon the fact thatsomeof thesampleswere very tough and could dominant the other sensory attributes. The second experimentby Dransfieldet al.41 concentratedon only one laboratorysupplying meat (UK) and producing two types of animal, Charollais cross steersand Galloway steers.Meat was exchangedbetweenBelgium, Denmark, the UK, France,Germany,IrelandandItaly. Two producttypeswereused,sirloin steaks and cubesof m.semimembranosusfor a casserolingprocedure.Again it was shownthattextureand,in thisexperiment,juicinesswerestronglyrelatedbetween countries,but againflavour could not be predictedaccuratelybetweencountries. The authorssuggestedthat different culinary practicescould haveaffectedthis result since the endpoint temperaturesthat the steakswere cooked to varied betweencountriesandit is known that this affectseatingquality. In a more recentstudy on lamb meatby Sanudoet al.,43 samples of lamb werepurchasedin Spainandoneloin from eachlambexportedto theUK. Both panelsusedtheir own methodsof sensory analysis,whereby UK usedeight- point category scalesandSpain used100mm line scales.The two panelsused the same descriptors and both panels achieved the same results and interpretation of the results. In this trial a hedonic scale for preferencewas included andit is interestingthat thepanelsagreedon termssuchaslambodour intensity, tenderness, juiciness,lamb flavour intensity. However, in hedonic (preference) ratingsthe Spanishpanelpreferred the Spanish lamb and the UK panelpreferredBritish lamb. 9.7 Conclusions Sensory analysis is an importanttool in meatscienceandis becoming accepted as a necessary part of meat quality experiments. Advances in computer technologyasameansof datacaptureandanalysisfacilitatesmoresophisticated statistical methods to be used by sensory analysts. As new instrumental technologiesaredeveloped,for example electronic noses,the interrelationships between these techniquesandsensorymethodsneedexploring.Work by Annor- Frempong43 on ‘boar taint’ hasalreadyshown it is possible to classify ‘boar Sensory analysis of meat 189 taint’ with an electronic nosein a way that is very similar to that obtained by a panel. A reviewby Schaller et al.44 identifies nineproduct areas, includingmeat andfish, where this technology is providingusefulinformation.Despiteall these advancesthe basic procedures outlinedearlier, where it is necessary to screen, train and monitor a panel, are still a vital requirement to produce effective sensory results. 9.8 References 1. TIL GNER, D.J. Anal i za organoleptyczna zywnosci , Warszawa: Wydawnictwo przemysluLekkiego I Spozywczego.1957. 2. MASUYAMA, G. and MIURA S. Handbook for Sensory Tests in Industry. Tokyo, Japan: JusePublishers, 1962. 3. AMERINE, M.A., PANGBORN, R.M. and ROESSLER, E.B. Principles of Sensory Evaluation of Food. New York, USA: AcademicPress1965. 4. JELLINEK, G. Sensory Evaluation of Food, Theory and Practice. Ellis Horwood, Chichester, UK. 1985. 5. MEILGAARD, M., CIVILLE, G.V. and CARR, B.T. Sensory Evaluation Techniques.Florida, USA, CRC Press1991. 6. COCHRAN, W.G. and COX, G.M. Experimental Designs, second edition. Chichester,UK., JohnWiley andSons Inc., 1992. 7. GACULA, JR,M.C. andSINGH, J. StatisticalMethodsin Food and Consumer Research, London,AcademicPressInc., 1984. 8. NALLY, C.L. Implementationof ConsumerTastePanels.Journal of Sensory Studies, 1987,2, 77–83. 9. BSI ASSESSORS FOR SENSORY ANALYSIS. BS7667, part 1. Guide to the selection, training and monitoring of selected assessors.1993/ISO 8586– 1:1993. London,BSI, 1993. 10. CROSS,H.R.,MOEN, R. andSTANFIELD, M. Training andtesting of judgesfor the sensoryanalysis of meat quality. Food

Technology, 1978 32, 48–52 and54. 11. WOOD, J.D., NUTE, G.R., FURSEY,G.A.J. and CUTHBERTSON, A. The Effect of Cooking Conditions on the Eating Quality of Pork. Meat Science, 1995, 40, 127–135. 12. DRANSFIELD, E. Intramuscular composition and texture of beef muscles. Journal of Science and Food Agriculture, 1977,28, 833–842. 13. BSI SENSORY ANALYSIS OF FOOD. PART 2. Paired comparison test. BS 5929,1982. London,BSI, 1982. 14. THIEME, U. and O’MAHONY, M. Modifications to sensory difference test protocols: The warmed up paired comparison, the single standard Duo- Trio andthe A-Not A testmodified for responsebias.Journal of Sensory Studies, 1990,5, 159–176. 15. VAN DER MAREL, G.M., DE VRIES, A.W., VAN LOGTESTIJN, J.G. and MOSSEL, D.A. Effect of lactic acid treatment during processing on the sensory 190 Meat processing quality and lactic acid content of fresh broiler chickens. International Journal of Food Scienceand Technology, 1989,24, 11– 16. 16. BSI SENSORYANALYSIS OF FOOD. PART 3. Triangular test. BS5929,1984 London,BSI, 1984. 17. KUNERT, J. and MEYNERS, M. On the triangle test with replications.Food Quality and Preference, 1999, 10, 477–482. 18. DACREMONT, C. andSAUVAGEOT, F. Are replicateevaluations of triangular testsduring a session goodpractice?Food Quality and Preference, 1997, 8, 367–372. 19. DRANSFIELD, E., NUTE, G.R. and FRANCOMBE, M.A. Comparison of eating quality of bull andsteer beef.Animal Production, 1984,39, 37–50. 20. DRANSFIELD, E., NUTE, G.R., HOGG, B.W. and WALTERS, B.R. 1990.Carcass and eating quali ty of ram, castrated ram and ewe lambs. Animal Production, 50, 291– 299. 21. ASTM (AMERICAN SOCIETYFORTESTINGAND MATERIALS) Standard practice for the determination of odour and taste thresholds by forced-choice ascendingconcentration seriesmethodof limits. Philadelphia, PA, USA, ASTM, 1991. 22. ANNOR-FREMPONG,I.E., NUTE, G.R.,WHITTINGTON, F.W. andWOOD, J.D. The problem of taint in pork:1. Detection thresholdsand odour profiles of androstenoneandskatolein a model system. Meat Science, 1997, 46, (1) 45–55. 23. BSI SENSORYANALYSIS OF FOODPART8. Duo-trio test. BS5929/ISO10399. London,BSI, 1992. 24. JANKY, D.M. and SALMAN, H.K. Influence of chill packagingand brine chilling on physicaland sensory characteristics of broiler meat. Poultry Science, 1986,65, 1934–1938. 25. BSI SENSORYANALYSIS OF FOOD. Part5. ‘A’ – ‘not A’ test.BS 5929/ISO 85881987.London,BSI, 1988. 26. BSI SENSORYANALYSIS OFFOOD.Part6. Ranking. BS 5929, 1989.London, BSI, 1989. 27. SHEARD, P.R.,TAYLOR, A.A., SAVAGE, A.W.J., ROBINSON, A.M., RICHARDSON, R.I. andNUTE, G.R. Factorsaffectingthecomposition andamount of ‘white exudate’from cookedbacon.Meat Science, 2001,59, 423–435. 28. MEILGAARD, M.C., CIVILLE, G.V. and CARR, B.T. Sensory Evaulation Techniques. BocaRaton, USA, CRC Press, 1991. 29. LAWLESS, H.T. andMALONE, G.J.The discriminative efficiency of common scalingmethods. Journal of SensoryStudies, 1986,1, 85–98. 30. LAWLESS,H.T. andMALONE, G.J.A comparisonof rating scales:Sensitivity, replicatesandrelative measurement.Journal of Sensory Studies, 1986,2, 155–174. 31. RISKEY, D.R. Use and abusesof category scales in sensory measurement. Journal of SensoryStudies, 1986,3/4, 217–236. 32. O’MAHONY, M. Sensory adaptation. Journal of SensoryStudies, 1986,3/4, 237–258. Sensory analysis of meat 191 33. WOOD, J.D., BROWN, S.N., NUTE, G.R., WHITTINGTON, F.M., PERRY, A.M., JOHNSON, S.P.andENSER,M. Effects of breed,feedlevel andconditioning time on the tendernessof pork. Meat Science, 1996,1/2, 105–112. 34. SHEARD, P.R., NUTE, G.R., RICHARDSON, R.I., PERRY,A.M. and TAYLOR, A.A. Injection of water andpolyphosphate into pork to improve juicinessand tendernessafter cooking.Meat Science, 1999,51, 371–376. 35. NUTE, G.R., JONES, R.C.D., DRANSFIELD, E. and WHELEHAN, O. Sensory characteristics of ham and their relationships with composition, viscoelasticity and strength. International Journal of Food Science and Technology, 1987,22, 461–476. 36. GOWER, J.C. Generalised ProcrustesAnalysis. Psychometrika, 1975, 40, 33–51. 37. LANGRON, S.P.The StatisticalTreatmentof Sensory Analysis Data.Ph.D. Thesis, University of Bath, UK, 1981. 38. FISHER,A.V., ENSER,M., RICHARDSON, R.I., WOOD, J.D., NUTE, G.R., KURT, E., SINCLAIR, L.A. and WILKINSON, R.G. Fatty acid composition and eating quality of lamb types derived from four diverse breed X production systems. Meat Science, 2000,55, 141–147. 39. SAVAGE, A.W.J.,DONNELLY, S.M., JOLLEY, P.D.,PURSLOW,P.P.andNUTE, G.R. Theinfluenceof varyingdegreesof adhesionasdeterminedby mechanical tests on sensoryand consumeracceptance of a meat product. Meat Science, 1990,28, 141–158. 40. DRANSFIELD, E., RHODES, D.N., NUTE, G.R., ROBERTS, T.A., BOCCARD, R., TOURAILLE, C., BUCHTER, L., HOOD, D.E., JOSEPH,R.L., SCHON,I., CASTEELS, M., COSENTINO, E. and TINBERGAN, B.J. Eating quality of European beef assessedat five ResearchInstitutes.Meat Science, 1982,6, 163–184. 41. DRANSFIELD, E., NUTE, G.R., ROBERTS, T.A., BOCCARD, R., TOURAILLE, C., BUCHTER, L., CASTEELS, M., COSENTINO, E., HOOD,D.E.,JOSEPH,R.L. SCHON,I. and PAARDEKOOPER, E.J.C. Beef quality assessedat European Research Centres.Meat Science, 1984,10, 1–20. 42. SANUDO,C.,NUTE, G.R.,CAMPO,M.M., MARIA, G.,BAKER, A., SIERRA,I., ENSER, M. andWOOD,J.D.Assessmentof commerciallambmeatquality by British andSpanishtastepanels.Meat Science, 1998,48, 1/2, 91–100. 43. ANNOR-FREMPONG,I.E., NUTE, G.R.,WHITTINGHAM, F.W. andWOOD, J.D. The measurementof the responsesto different odourintensitiesof ‘boar taint’ using a sensory panel and an electronicnose.Meat Science, 1998, 50, 139–151. 44. SCHALLER, E., BOSSET, J.O. and ESCHER. F. Electronic Noses and Their Application to Food. Lebensm.-wiss. u.Technol., 1998,31, 305–316. 192 Meat processing 10.1 Introduction On-line monitoring of quality for meat processing involves two main activities. Firstly, individual carcasses or primal cuts are selected whose meat reaches a required standard for premium products such as cured hams or in-flight meals. Probes, ultrasonics and video image analysis (VIA) are available. Obtaining access to interior muscles, and variation between and within carcasses are the main problems. Being able to predict meat quality from on-line measurements has great commercial potential, especially for tenderness and water-holding capacity (WHC), but we can allow no contamination, only imperceptible damage, and measurements must be very fast to keep pace with line speeds. Secondly, for the processing of comminuted meat, information from on-line sensors is used for process control in emulsion formation, curing or cooking. Operating conditions are relatively simple if the product can be accessed in homogenised batches or in a continuous stream. There is usually ample time for integrated measurements. 10.1.1 Apparatus Despite the tremendous commercial advantages offered by on-line monitoring of meat quality, relatively few methods are available as off-the-shelf purchases. Apparatus that may be simple to build, develop and test in a laboratory with skilled operators and convenient operating conditions is seldom profitable to develop commercially for use in severe industrial conditions. Developers of scientific apparatus usually think in terms of hundreds or thousands of units to be manufactured, not ones and twos. The meat industry is reluctant to spend 10 On-line monitoring of meat quality H. J. Swatland, University of Guelph much unlessapparatusis proven beyonddoubt. Thus,smallmarketsandlack of vision combinein a viciouscircle to perpetuatevintagetechnology suchasglass pH electrodes. However,a few meatprocessors havecommissioned their own technologyandaresecretly reapingtherewards.Commercialsecretsareseldom publicised in research papers,so this chapter can offer only an academic perspectiveon the subject. Apparatuscomesin severalformats. VIA is remote. The camerais located some distance from the side profile of a carcass or a sectioned rib-eye. Ultrasonictransducers,however,areplacedin contactwith thesample,usuallya carcass.Orthogonality must be maintained to form an imageof soundwaves reflected from muscle-fat boundaries. Spectrophotometric methodsmay be remote, asfor a plateof comminuted product placedin a colourimeteror near- infrared (NIR) spectrometer. But, using optical fibres (Kapany, 1967), spectrophotometric methods may be adaptedasprobesto pushinto the carcass or form awindowagainstacomminutedproduct(MacDougall andJones,1980). Optical fibres pushedinto meatdo not give the same reflectance spectrumas obtained with a conventional reflectometer (Fig. 10.1). When pushedinto a carcass,the probe may be combined with a depth detector to give a spatial dimension to the data.For example, reflectancemay be plottedversusdepth in thecarcass. This is calleda transect.A thin probeminimisestissuedistortionbut supports only a smallopticalwindow.This reducesthevolumeof tissuethrough which reflectanceis integrated, sothatnon-muscle tissues at theopticalwindow maycreateanomalousspectrawhich do not represent musclequality (Brøndum et al., 2000).Electromechanicalprobes havea long history for predicting meat toughness.A torqueprobeis currentlyavailable (Jeremiah andPhillips, 2000). Fig. 10.1 Reflectancespectraof pork measuredwith optical fibres (a) andwith a reflectance(b). Line c is line a raisedto the third powerof wavelength. 194 Meat processing 10.2 Measuring electrical impedance Muscle hasa relatively low electrical resistance while fat hasa high resistance. Muscle contains continuous electrolytes with a relatively high conductivity, while fat is dominatedby globulesof insulating lipid. This enablesthedepth of subcutaneousfat to befoundalong a transect,overall lipid contentto bedetected electromagnetically, andexudative meatto be detected by high conductivity. Electrical impedancemeasurementswerefirst madein Englandin the1920s and1930sasDFD (dark, firm, dry) pork becamea problemwhenshipping of pigsby rail to newcentralisedabattoirs replacedlocal slaughtering.Penetration of curing ingredientsfor traditional dry curing is dangerously slow but, when diffusion is furtherreducedby a paucityof extracellular fluid, it mayallow deep spoilage. Banfield (1935) found the main factors to be: (i) curing salt concentration,(ii) volumeof pickle pumped into the meat,(iii) intrinsic texture andmoisture content of the meat, (iv) ambienttemperature,(v) fat-freesurface area for pickle penetration, and (vi) volume of meat relative to pickle. Penetration of curing salts was monitored on-line by testing the electrical resistance of the meat (Callow, 1936). This led to the discovery of pH-related variability in the resistanceof freshpork (Fig. 10.2),which now we mayuseto placepork on a scalefrom DFD to PSE(pale,soft, exudative). 10.2.1 Biophysical source Skeletal muscle is composedof myofibres. Theseare extremely large cells, althoughreaching only about0.1mm in diameter theymaybemany centimetres in length. Like all other cells,myofibresaresurrounded by a plasmamembrane with strongdielectric propertiesanda capacitance of approximately1 Fcmÿ2. Thus, the cell membrane is a very effective insulator, and when meat probe Fig. 10.2 The

relationshipof impedanceat 50Hz to the ultimatepH of freshpork discoveredby Callow in 1936. On-line monitoring of meatquality 195 electrodesareinsertedinto the muscle of a recently slaughteredcarcass, strong overall capacitanceis detectable. 10.2.2 Polarisation For metalelectrodesin contactwith electrolyteswithin andbetweenmyofibres, anelectrodedischargesionsinto thefluid while ionsin thefluid tendto combine with anelectrode.This maycreate a chargegradientacrossanelectricaldouble layer sothat theelectrode-electrolyte interfacebehaves asa voltagesource,and as a capacitor in parallel with a resistor. The magnitude of this polarisation dependson: (i) themetallic compositionof theelectrode;(ii) electrodearea;(iii) electrode insulation by adipose cells; (iv) current density and electrode separation; (v) post-mortem changes in electrolyte composition; (vi) temperature; and (vii) the frequency of the test current, such that resistance andcapacitancein parallel areusuallyinversely proportional to thelogarithm of frequency.Polarisation in meat probesmaybecancelled by usingAC instead of DC, and by using separate source and detectorelectrodes. For example, with four electrodes,two supply the testcurrentandtwo detectit. 10.2.3 Resistance, capacitance and anisotropy Impedanceis determined by resistanceandcapacitance(capacitive reactance), but these maybein seriesor parallel(Gielenet al., 1986).Capacitance(CS) and resistance(RS) in seriescircuit are relatedto their equivalents in parallel as follows, Rs ˆ Rp=…1‡ …2fCpRp†2 …1† Cs ˆ Cp…1‡ …1=…2fCpRp†2† …2† As well asthe intrinsic dielectric anisotropyof meatcausedby myofibresbeing parallel (EpsteinandFoster, 1983),other factorsareinvolvedin makingon-line measurements. Plate electrodesmay be used for excised or comminuted muscles,but carcassmeasurements require probes.A pair of probeelectrodes may be inserted in three different planesrelative to the longitudinal axesof myofibres. When electrodes and myofibres are coaxial, myofibres may be compressedconcentrically around the electrodesto increasecapacitance from membranes.But if electrodesopen up channels of extracellular fluid along myofibres, this shorts the test current and reducesthe current density on membranes.Thus, online useof electrical probesrequiresstandardisation of electrodeplacement relative to myofibre orientation. 10.2.4 Electrode penetration Depth of electrodepenetration may determine the areaof electrodecontact and thecurrentdensitybetweentheelectrodes.Contactareashould becontrolled by 196 Meat processing an insulatedsleevecovering the baseof the electrode so that exposure to the meatis constant. Surfacewetnessonacarcassmayvary andit maybenecessary to dry the carcassat pointsof measurementto avoid surfacefluid shortingthe electrodes.Even if the distance between electrodesis set by a manufacturer, electrodesmay becomebent. Moving the electrodescloser together decreases resistance, but may increasecapacitance. 10.2.5 Freezing Freezingobscuresany initial differencesin impedance, probably because ice crystalscut throughcell membranesto createa continuous pool of electrolytes when the muscleis thawed. This providesa methodfor the detectionof meat that hasbeenfrozen and thawed, relative to meat that hasneverbeenfrozen (Salé, 1972). 10.2.6 PSE detection Pioneer research was undertakenby Rowanand Bate Smith (1939), but their discoveries lay dormant until the late 1970s, when attempts were made to developbettermethodsthanglasspH electrodesfor sorting anddetecting PSE pork carcasses.Several commercial systems becameavailable in the 1980sto measure the electrical properties of pork, such as the MS-Tester and the Carnatest. As well as pork, impedancetesting may be usedto identify PSE turkey meat(Aberle et al., 1971).The MS-Tester measuresthe dielectric loss factor of pork usinga frequency synthesisercombined with ananalogto digital converter. With conductivity and dielectric constantr , the dielectric loss factor d d =r …3† is found from the cotangentof the measuredphaseangle(PfütznerandFialik, 1982).The TestronMS-testerusestwo parallelscalpelblades25 mm apart at 15 kHz (Kleibel et al., 1983). DFD, normalandPSEcategoriesareseldomdiscreteandusuallyoverlapasa continuum. Separationis further complicatedby the non-linear relationshipof impedance with meat quality, as shown for the MS-Tester by Seidler et al. (1987). When capacitance in parallel (Cp) and resistance in parallel (Rp) are relatedto frequency (f), the quality factor (Q) is definedas, Qˆ 2 f CpRp …4† The other term in commonuseis the dissipationfactor, D ˆ 1=Q …5† The MS-tester may be capable of differentiating between normalandPSEpork as early as an hour or less post-mortem(Kleibel et al., 1983), but this is not alwayspossible (Schmittenet al., 1984;Fortin andRaymond,1988). On-line monitoring of meatquality 197 10.2.7 Adenosinetri phosphate Adenosinetriphosphate(ATP) providesenergyfor muscle contraction and the maintenance of ion gradients across membranes such as those of the sarcoplasmic reticulum. The conversion of extensible living muscle to inextensiblemeatis determined by the length of time that anaerobic glycolysis canmaintain ATP levels from stored glycogen.Impedanceoften appears to be correlatedwith pH, asin Fig. 11.2,but a morefundamentalrelationship maybe between capacitance and ATP concentration. If lactate-induced damageto ion pumps in cell membranesis postulatedasthe primary causeof the decreasein impedance as the pH declines post-mortem, then DFD beef with a relatively high pH should havehigh impedance.This doesnot appear to be the case. In beef, Cp maybecorrelatedwith ATP, r ˆ 0:8, whereascorrelationsof Cp with pH areweakerandsporadic in occurrence(SwatlandandDutson,1984).Thus, the postmortemdecline of Cp is probably determined more by the leakageof ATP-driven ion pumps thanby a direct effect of pH on cell membranes. 10.2.8 Electromagnetic scanning Whenan animalor carcassis passed at a constantvelocity througha magnetic field, skeletal muscles createa measurable perturbationin the magnetic field. For live animals, this principle wasusedin theEMME (modelSA-1, electronic meat measuringequipment, EMME Corp., Phoenix, Arizona), then in the TOBEC (total body electrical conductivity) HA2 for measuringadiposity in humans. The manufacturerof the TOBEC (Agmed Inc., Springfield, Illinois) thenestablisheda subsidiary (Meat Quality Inc.) to produceequipmentfor on- line evaluation of the fat contentof meat, the MQI ElectromagneticScanner. A perturbation in a magnetic field is difficul t to standardise or expressin scientific units. Thus, a phantom sampleis usedfor standardisation. Carcass shapes arecomplex, so electromagnetic scanning is well suitedfor the analysis of boxed beef. The Emscan MQ27 system used in Australia uses a coil frequencyof 2.5MHz. Thephaseangle betweenthevoltageandthecurrent,and the amplitude of the current are measured at 50Hz giving a lean meat computationoutput at 20Hz. As a pork carcasspasses through the coil of the MQ25, a relative energy absorption curve is generated, and the curve is scaledfrom the height and position of the major peak. Predictions are possible to line speeds of 1,000 carcassesper hour. If temperature is taken into account, electromagnetic scanning results maybecombinedwith carcassweightto give a strongpredictor of total lean(R2ˆ 0.904). 10.2.9 Bioelectrical impedance A fourelectrode bioelectrical impedance analyser (RJL Systems Detroit, Michigan) hasbeendevelopedto predict carcasslean content. The electrodes are21-gaugeneedlesplacedin an anterior to posterior sequencealongthe full 198 Meat processing length of the animal’s back with a 10-cm separation between transmitter and detector electrodesat eachend.For lamb, prediction equations (R2ˆ 0.97) for total weight of retail cuts were developedusing resistance,reactance,weight, distance betweendetectorelectrodesandtemperature.Measured along the side of pork carcasses,the prediction of lean yield (R2ˆ 0.81) is lessaccurate than TOBEC, but may be usedfor both live animalsandcarcasses(Swantek et al., 1992). Marchello and Slanger (1992) found that the methodwas suitablefor robotic sorting of pork shouldersaccording to lean content. 10.3 Measuring pH ThepH of living skeletalmuscleis usuallyjust abovepH 7. It maydecreaseafter slaughterto pH 5.4 to 5.7 in normal meat.If initial glycogenis limited, the pH stayshigh andthemeatremainsDFD (asit is in thelive animal).If thepH decline is rapid (affecting muscleproteinswhile still warm) or extensive(giving a low ultimatepH), themeatbecomesPSE.Thus,thepH of meathasa profoundeffect on colour, firmnessandwater-holdingcapacity,aswell assubtleeffectson taste, tendernessand rate of post-mortemconditioning. The pH of meat may be measuredon-line with a gel-filled combinationelectrode,but the risk of broken glassmaybeunacceptable.Ruggedportableequipmentfor routineon-line usein commercialplantsis available(NWK Binär GmbH,Landsberg,Germany). An unofficial terminology hasdevelopedamongmeat scientists.Subscripts are appended to indicate time of measurement.The two classicalmeasuring timesare45 minutesand24 hourspost-mortem.Thesemaybe termedpH1 and pH2, respectively, or pH45 andpH24. Othersubscriptsmayappear,suchaspH30 for a measurement at 30 minutes post-mortem. The context usually shows whether the subscript is in minutesor hours.This may not be precise, but it is convenient. Working in a commercialenvironmentit is very difficul t to ensure the accuracyof timespost-mortem. 10.3.1 PSE in pork A pH1< 6.0 is typically takenas the critical point below which commercially importantPSEdevelopsin pork (BendallandSwatland,1988).ThepH1-indexis definedasthe percentof pH1 valuesbelow pH 6.0 at 45 minutespost-mortem. The following equations may be usedto relate the meanpH1 to the pH1-index: for meanpH1 > 6:33: pH1 ÿ index ˆ 37:8 …6:65ÿ pH1† …6† for meanpH1 < 6:33: pH1 ÿ index ˆ 110:3 …6:39ÿ pH1† …7† 10.3.2 Conditions of measurement Many factors affect pH measurementson-line, particularly the difficulty of establishing electrical contactwith the referencecell of a glasselectrodeif the meatis dry. Meat may be homogenisedin potassiumchloride and iodoacetate On-line monitoring of meatquality 199 solution to arrestglycolysis (Bendall, 1973). Corrections for temperature are required.Theeffectof temperatureis to lower thepH by 0.1–0.15unitsper10ºC rise in temperature and to raise it by the same amount per 10ºC fall in temperature(BendallandWismer-Pedersen,1962).This is caused by changes in the pK valuesof carnosine,anserine andhistidinebuffers in meat. 10.3.3 Light scattering Meatwith a high pH appears darkwhile meatwith a low pH appears pale.This is causedby differences in light scattering.Incidentlight is transmitteddeepinto meat with a high pH andvery little escapesto beseenby theobserver. Incident light haslimit edpenetration of meatwith a low pH andmostof it escapesfrom the meat to be seenas palenessby the observer. For measurementsmade by reflectancespectrophotometry therefore,meatwith a high pH hasdeeper bands of selective absorbance (becausethelight pathis longerthanin meatwith a low pH). Light scattering may be measured on-line for the direct prediction of the appearanceof the meat,for eitherPSEor DFD (Gariépy et al., 1994),or asan indirect way of measuring other pH-relatedproperties such as water-holding capacity (Andersenet al., 1999). 10.3.4 Biophysical source Three factorsmay contribute to high light scattering in meatwith a low pH. Firstly,

BendallandWismer-Pedersen(1962)proposed that light scattering at a low pH is causedby denaturation of sarcoplasmic proteins, similar to heat denaturationof eggalbumen (Bendall, 1962).Precipitatedprotein is detectable histologically in severe PSE pork (Bendall and Wismer-Pedersen, 1962). Secondly, anotherfactoris thatshrinkageof myofibrils at a low pH increasesthe refractiveindexdifferencebetween myofibrils andsarcoplasmsothatscattering from the myofibrillar surfacemay be increased (Hamm, 1960; Offer et al., 1989). Myofibrils account for approximately 80% of the volume of pork, declining to 50% as the pH declines post-mortem. Thus, even small optical changes in the myofibrils havea major effect. A third factor is that increased myofibrillar refractive index causedby low pH may increasescatteringby increasing the refractive deflection of light passing through myofibrils. Myofibrils are strongly birefringent, as indicated by the naming of A (anisotropic) and I (isotropic) bands,and this enablesthem to be investigated with polarised light. Measurementson individual myofibres show that the optical path difference(between rays following different refractive pathways allowed by birefringence)tendsto increase when pH is decreased. 10.3.5 Laser scanning Laser scanningof meat was introduced by Birth et al. (1978), basedon the Kubelka-Munk analysisof light scattering.Illuminating the uppersurfaceof a slice of musclewith a helium-neon lasergives: 200 Meat processing log MT ˆ Aÿ Br …8† whereMT is theradiantexcitanceonthelowersurface,A is theinterceptandB is theslope of a regression (light intensity versusdistance),andr is thepathlength throughthe meat.Birth et al. (1978)showed that Bˆ log2…S‡ K† …9† where S is a scatter coefficient (cmÿ1), and K is the absorptioncoefficient (cmÿ1). B may be called a spatial measurement of scattering,for the sakeof convenience.Birth et al. (1978)showedthat spatialmeasurementsof scattering arerelatedto meatquality. 10.4 Analysing meat properties usingNIR spectrophotometry NIR spectrophotometry hasmany certifiedapplicationsin food analysis (Norris, 1984),especially for the fat content of mince or groundbeef (Tøgersenet al., 1999).It is ideal for platesandcontinuousstreamsof comminutedmeatproducts (Isaksson et al., 1996), but hasalsobeenusedfor carcasses(Chen,1992;Chen and Massie, 1993). It may be usedto predict functional propertiesof meat in processed products and to detect previously frozen meat (Downey and Beauchene, 1997). 10.4.1 Apparatus Typical componentsare a tungsten-halogen source, a grating monochromator from 800to 1100nm,anoptical systemto directthelight throughor ontoaplate of comminutedmeatand a photometer. Multiple scanning and rotation of the samplehelp to averageheterogeneity, andsmoothed absorbance measurements at about100 wavelengths may be usedto make predictionsfrom a partial least squareschemometric calibration. Technical problemsoriginate from drying of the sample surface, pH-related changes in light scattering, metmyoglobin formation, and sampletemperature. Theseoften limi t the applicability of a prediction equation to situationsexactly the sameasthe calibration population. Because NIR spectrophotometry is sensitive to fat content, and fat content has manyeffects on product quality, it may be difficult to extractinformationthat relatesdirectly to protein functionality. 10.5 Measuring meat colour and other properties Theoxygenation of purplemyoglobinto redoxymyoglobin, andtheoxidation of oxymyoglobin to brown metmyoglobinarevitally importantfor the appearance of meatproducts, asis the formation of heat-stable,pink nitrosylhaemochrome in curing (Fox, 1987). This latter reaction is so sensitive to nitrite that even nitrite from spices and tap water may prevent browning in cookedproducts. On-line monitoring of meatquality 201 Carbonmonoxide mayhavea similar effect (evenfrom exposure of transported animals to traffic fumes). Myoglobin is also important in connectionwith oxidative rancidity. Haemoglobin, althoughminimal in properly exsanguinated meat, may inadvertently be introduced from bone marrow in mechanically deboned meat. 10.5.1 Spectrophotometry The Soret absorbance bands of deoxymyoglobin, oxymyoglobin, and metmyoglobin occur at 434, 416, and 410 nm, respectively (Bowen, 1949; Morton, 1975).The oxygenation of myoglobin causesa lossof the absorbance bandat 555nmandtheappearanceof two newabsorbancebandsat 542and578 nm with milli molarabsorptiviti esof 13.2 and13.3,respectively(Morton, 1975). Working on-line with muscle surfacereflectance is more difficult than the spectrophotometry of purified pigments in solution. Using reflectance spectrophotometry, RayandPaff (1930)foundthat542 and578nm absorbance bandswere of equal intensity. But many published studies are of artificially stabilised surfaces.Subsurfaceoxidation of myoglobin may produce strange results on-line (becausescattering is changed as well as the absorbance spectrum). From absorbance spectrophotometry of purified metmyoglobin, the secondaryreflectancepeakof metmyoglobin around 600nm mayencompass an additional small peak at 565 nm. If cut meat surfaces are exposed, product colour canbe measured on-line by VIA (Lu et al., 2000). Spectrophotometryvia optical fibres may be used to assessthe functional propertiesof comminutedmeat(SwatlandandBarbut,1990).Formixturesof pork adiposetissueandbeefmusclewith a low connectivetissuecontent,reflectanceat 1000nm may be correlated with lipid content (r ˆ 0.99), at 930nm with centrifugationfluid loss(r ˆ0.77),andat 1000nm with cookingloss(r ˆ0.99). Correlationsmay be weakenedwhen the meat is adjustedto a constantlipid content;for example,for pork musclereflectanceat 780 nm wascorrelatedwith pH (r ˆ ÿ0.80),at 690nmwith centrifugationfluid loss(r ˆ 0.74),andat 710nm with cooking loss (r ˆ0.63). Peak correlationswith functional propertiesare highly wavelengthdependent.In the first set of correlationsgiven above,lipid contentis themajorvariableandthestrongestrelationshipsareobtainedwith red or NIR. But if variationin lipid contentis cancelledsothatpH-dependentprotein propertiesaredominant,thenthe peakcorrelationsarewith shorterwavelengths. Thus,in experimentalstudiesaimedat finding the mostsuitablewavelengthsfor simple on-line sensors,the likely importanceof lipidrelated versuspH-related sourcesof varianceshouldbe considered. With regard to cost-effectiveness, full-range spectrophotometry must necessarily bemore expensiveandmorecomplex thana simplemonochromatic sensor. But in choosingthelessexpensive andmorerobust option,it is essential to know the whole spectral rangeof correlations.Sometimes, correlationsof reflectancewith a functional property are strong at a certain wavelength, but weak at an adjacentwavelength. If both wavelengths are encompassedwithin 202 Meat processing the broad-bandrangeof a simplesensor, thenthe results may be disappointing. But a narrow spectral rangeimplies weaklight intensity, thuseither increasing the costor the relative noiseof the photometer. 10.6 Water-holding capacity Water-holding capacity(WHC) may be definedasthe ability of meatto retain its own waterunderexternal influencessuchascompression or centrifugation. In this case, water-bindingcapacity becomestheability of themeatto bind extra wateraddedto a product.Waterabsorptionor gelling capacitymay be defined as the ability of meat to absorb water spontaneously from an aqueous environment. The basic mechanismis the effect of pH on the myofilament lattice. As pH declines towards the isoelectric point of muscle proteins, a reduction in the negative electrostaticrepulsionbetweenmyofilamentsreduces the water spaceof the myofilament lattice. The releasetime of this fluid, however, is highly dependenton timetemperatureinteractions, muscle structure andhandling. The usualmethodfor predicting WHC on-line is to exploit a correlation of WHC with pH and, indirectly, with light scattering(Jaud et al., 1992) or conductivity (Lee et al., 2000).The usualproblemis weak correlations,often from curvilinearrelationships.NIR reflectancemeasuredwith a probeat 30 min postmortem can predict 24 hour fluid lossesfrom pork, but the measurement takessix minutes(Forrestet al., 2000). 10.7 Sarcomere length Sarcomerelengthhassomeimportanteffectson meat quality. If a musclesetsin rigor mortis at a shortened length, there is a high degreeof overlap between thick and thin myofilaments.The meat is tough and hasa low WHC. A laser diffractometermay be usedto measure sarcomerelength, Sarcomere lengthˆ =sin …10† where is theanglesubtendedby the first orderdiffraction bandrelative to the opticalaxis.Because theanglesarerelatively small,sin ' tan (Rome,1967). However, this methodrequires the dissection of individual or small bundlesof myofibres,andis no more useon-line thanis light microscopy. Bulk meatwith high scattering from countlessmyofibrespresents a real challenge. With two plane polarisers (a fixed polariser and rotatable analyser), the maximum transmittance occurs when the analyseris rotated parallel to the polariser, and the minimum is when the analyser is perpendicular to the polariser. But if the polariser is at 0º, when the analyseris at 90º, then a birefringent musclesamples with myofibres at 45º between the polariser and analyserrotateslight sothatnow it maypassthroughtheanalyser.Thebrightest On-line monitoring of meatquality 203 bandsarethe A bands,wherethick (myosin)andthin (actin) filamentsoverlap. But maximumtransmittancenow is at an analyserangle >90º, becauseof the optical pathdifferenceof the myofibre. NIR is usedto minimisescatteringandenablesmeasurementsto bemadeon thin slices. The transmittanceof NIR polarised light increases as sarcomere length increases from 1.2 to 1.5m, it peaksat sarcomere length 1.5m, then decreasesas sarcomere length increases to 3.5m. Thus, if thereare no cold- shortened sarcomeres, thetransmission of polarisedNIR maybecorrelatedwith sarcomerelength (Fig. 10.3),andwith functionalproperties in meatprocessing. For example,NIR birefringenceis correlatedwith WHC andcooking lossesin processed turkey meat (r ˆ 0.8 and r ˆ ÿ 0.82, respectively; Swatland and Barbut 1995),anda probefor on-lineusehasbeendeveloped(Swatland,1996). 10.8 Connective tissue Connectivetissues suchaselastin andType I collagen arenotorious sourcesof meat toughness. Elastin is alwaysheat-stable, while Type I collagen may resist normal cooking if it is highly cross-linked, as in beef from an old cow. Gelatinised collagen is important in meat processing. It may be desirable in certain products, suchaspork piesandcookedhams.However, in excess,when it has beenaddedas a filler to a comminutedproduct, gelatin capsbecomea defect. 10.8.1 Carcassmeasurements Both elastin and collagen, as well as heatstablepyridinoline cross-links, are autofluorescent(Odetti et al., 1994).Whenilluminatedwith UV light at 370nm, Fig. 10.3 With polarisedNIR transmittedthroughpork, rotationof the analyser (degrees)affectsthe correlationof transmittancewith sarcomerelength. 204 Meat processing theyfluoresceblue-white from about400to 550nm.Measurementsmadewith a UV fibre-optic probemay be correlated with sensory tendernessof beef (Fig. 10.4;Swatlandet al., 1994). Themain problemis that connectivetissueis only onesourceof

beeftoughness.The probemay be effective for sorting carcasses in a population whereconnective tissuetoughnessis dominant, but may fail if someotherproblemsuchasshortsarcomerelength is dominant. 10.8.2 In meat processing Connective tissuelevels in groundbeef may be a problem if too many meat scrapswith a high content of tendon areworkedinto a product.The result may be a gritty texture for hamburger, or excessivegelatin formation in a cooked product. Elastin derived from elastic ligaments has virtually the same fluorescenceemission spectrum asType I collagenfrom tendonandligaments. This enablesfluorescence emission ratiosto be usedto predict total connective tissuelevels. Under experimental conditions, collagen fluorescence in comminuted mixtures of chicken skin and muscle may be measuredthrougha quartz-glass rod with a window onto the product (Swatland and Barbut, 1991). High proportionsof skin decreasethegel strengthof thecookedproduct(r ˆ ÿ 0.99), causing high cooking losses (r ˆ 0.99) and decreased WHC (r ˆ ÿ 0.92). Fluorescenceintensity may be strongly correlatedwith skin content (r > 0.99 from 460 to 510 nm) and, thus,may be strongly correlatedwith gel strength, cooking lossesand fluid-holding capacity (Fig. 10.5). Correlations would be weaker in a practical application, but still adequatefor feed-back control of product composition. Oneof theproblemsin calibration is pseudofluorescence – reflectanceof the upper edge of the excitation band-pass. This occurs because excitation and Fig. 10.4 UV fluorescencetransectsthroughbeefsemitendinosuswith high sensory toughness(line) and longissimusdorsi with low sensorytoughness(solid squares). On-line monitoring of meatquality 205 emission maximaare fairly close, and the filters and dichroic mirrors usedto separate excitation from emission are not perfect. Thus, the standard usedto calibratetheapparatusfor themeasurementof relativefluorescence shouldhave a similar reflectanceto meat.Cleanaluminium foil with a dull surfaceis a fairly close matchto meat. 10.9 Marbling and fat content Marbling is composedof clumps of adipose cells, mostly located between bundlesof myofibres.It is notoriously diffi cult to measure objectively. Unless elaborate precautions are taken using polarised light and spectrophotometric identification, VIA may fail to separatemarbling from connectivetissueand glisteningspecular reflectance.Marbling distribution is anisotropic (becauseit follows muscle fasciculi) and subjective grades may have a non-li near relationship to extractable lipid. Marbling may be detectedand distinguished from connective tissueusinga multichannelprobe(Swatland, 2000),but thereis little or no appli cation for meat processing. As increasing amounts of subcutaneousor intermuscularfat are comminutedtogether with lean muscle, reflectanceincreasesat all visible wavelengths until reaching the spectrum of 100%adiposetissue(FrankeandSolberg, 1971). 10.9.1 Yellow and soft fat Factors in the animal’s diet causing yellowing of fat (from carotene) and softening (low-melting point fatty acids)arereadilydetectablewith a fibre-optic probe(Swatland, 1988; Irie andSwatland,1992). Fig. 10.5 Spectraldistributionof the t-statisticfor the correlationof fluorescence emissionwith skin content(line), gel strength(solid squares)andcooking losses (emptysquares)in mixturesof chickenbreastmeatandskin. 206 Meat processing 10.10 Meat flavour On-line testingof meataromaand,hence,flavour is possible (Linforth, 2000). Thetechnologyfor thedetection of volatiles continuesto develop (Dickinsonet al., 1996; White et al., 1996).Chemiluminescencemay be usedto assess the conditioning of beef (Yano et al., 1996a) and for meatspoilage (Yano et al., 1996b.Semiconductorgassensors also aresuitablefor useon meat(Berdagué andTalou, 1993)andmaybeusedto identify varioustypesof meat(Neelyetal., 2001)andwarmed-overflavour (Grigioni et al., 2000). 10.11 Boar taint In North America, malepigs for meatproductionareusually castrated, despite deleteriouseffectson rateof growthandfeedefficiency. The primary reasonis therisk of boartaint in thefat. This is anunpleasantodourthatoccurswhenthe fat is heated.However, boartaint is only detectablein pork from youngmalesby a small percentageof consumers.Thus,the problemowes its notoriety to pork obtained from old boarsthat havebeenusedfor breeding, andit neednot be a problemin intact youngmalesslaughteredat a relatively light weight. A majorcauseof boartaint is theconcentrationof sexsteroidsin thefat, such as 5-androst-16-ene-3-one, commonly called androstenone. Androstenone smellsstrongly of animalurine.Othertesticular steroidssmell like musk. Other causesof boar taint include skatoleand indole, with a faecal odour produced from tryptophanin the gut. Carcassesmay be testedsubjectively on-line using a hot iron. Objective methodsareavailablefor skatole andandrostenone.Both requirea sample to be removedfrom the carcassfor analysis,but the methodsaresufficiently rapid to be consideredcommercially (Andersenet al., 1993). On-line testing for boar taint may be possible usingthe Alabaster-UV semiconductor system (Berdagué andTalou, 1993).The sensoris mounted in a stainless-steelchamber with a UV sourceandgasesareexposed to a cycle of ozoneandthenflushedby air. 10.12 Emulsions 10.12.1 Electrical method Theemulsifying capacityof meatmaybeevaluatedby progressivelyadding oil during the formation of an experimental meat emulsion (Cunningham and Froning,1972).Initially, theoil is trappedin a stable meat emulsionbut further additionof oil causestheemulsionto breakdown.Emulsionbreak-down maybe detected electrically (Webbet al., 1970).Electrodesarelocatedin an emulsion formedfrom salt-extractedmeat proteinsolution using a mixing propeller (Fig. 10.6). On-line monitoring of meatquality 207 10.12.2 Optical method During emulsionformation, the reductionin particle size causedby chopping haslittle opticaleffect.But theinclusionof air bubblesincreaseslight scattering, thusincreasing product paleness(Palombo et al., 1994).Scattering decreasesif battersarestoredor if thereis a redistributionof air from smallto largerbubbles. Thesechangesmay be monitoredusing fibre-optics,asin the gelation of whey proteins(Barbut,1996). 10.13 Measuring changesduring cooking 10.13.1 Temperature Many off-the-shelfmethodsareavailable. Iron-constantan andchromel-alumel thermocouples are in common use. A thermocouple uses two dissimilar electrical conductors to generate a thermoelectric voltage proportional to the temperature difference between the two end junctions. Junctions may be exposed or covered, and/or grounded. Alternatively, a thermistoris a resistive circuit component, usually a two-terminal semiconductor, whose resistance decreasesas temperature increases. Another method is to use a Callendar’s thermometer(platinum RTD probe)with a thin film or wire of pureplatinum. This hasahigh resistanceandfacilitatesmeasuringthechangein resistancewith temperature. Microwave cooking may be monitored with a temperature- sensitive fluorescent cap on a quartz optical fibre. Infra-red radiometers calibratedasthermometers areavailablefor remotesensingof temperature.The time constantis thelength of time thatasensor takesto readthetrue temperature of the sample. Heat conduction along wires to the sensor must be minimal. Signal transmitters may be requiredfor long wires. Fig. 10.6 Impedancechangesduring the formationandbreakof an emulsionasoil is added. 208 Meat processing 10.13.2 Colour changes Meatwith anappreciablemyoglobin concentrationchangesfrom redto greyish- brown when cooked(PearsonandTauber, 1984).The brown pigments formed during cooking include denatured globin nicotinamidehemichromes (Tappel, 1957),denatured myoglobin (Bernofskyet al., 1959),Maillard reactionproducts (Pearsonet al., 1962), metmyochromogen(Tarladgis, 1962) and haematin di- imadazole complexes(Ledward,1974).Failureof meat to brown is a common commercial problem, particularly with the nicotinamide-denatured globin haemachromesof cookedpoultry meat(Claus et al., 1994). Cooking increasesreflectance at most wavelengths, but especially around 560 nm (Fig. 10.7).Reductionbut not complete lossof myoglobinabsorbance around 560 nm also occurs.Between0 and 40ºC there are small changes in reflectance around the Soretabsorbance bandfor myoglobin but, for practical purposes, the colour may be regardedas constant. Above 40ºC, however, reflectance starts to increase,peaking at 70ºC, and then decreasingas the temperature is increased beyondthis. For eachwavelength, the slopefor the changein reflectance per degreeof temperature (R/t) is influencedby the magnitude of the initial reflectance. The slopeis high for reflectancepeaksandlow for valleys. This obscureswhat is really happening at different wavelengths. Correctionsmay be made by dividing the temperature slope (R/ t) for each wavelength by the mean reflectance for eachwavelength at all temperatures. This may be called the adjusted temperaturecoefficient for eachwavelength andis useful in finding the temperaturesat which majorchangesin colouroccur. Changesaround theSoret absorbance bandareparticularly complex (Fig. 10.8).To seehow thesechanges affectsubjectivecolourperception, chromaticity coordinatesmaybefoundfrom spectrausing the weighted ordinate method.The resultsare not correct (for reasonsevident in Fig. 10.1)but maybequiterevealing.For example,Fig. 10.9, Fig. 10.7 Progressivechangesin fibre-optic reflectanceaslambis cookedfrom 25º(a), to 50º (b), andto 80ºC(c). On-line monitoring of meatquality 209 shows that cooking of lamb (as in Fig. 10.7), causesonly minor changes in chromaticity coordinatesx andy, but major changesin paleness(Y). 10.13.3 Gelatinisation Initial heat-shrinkageof the endomysiumduring cookingcauses the expression of fluid from the myofibre, while later gelatinisationof the perimysium creates thecharacteristic textureof cookedmeat.Lossof collagen birefringencemaybe usedto monitor the gelatinisationof collagen (Fig. 10.10). Fig. 10.8 Adjustedtemperaturecoefficients400nm(a),430nm(b) and480nm(c) from the sameexperimentasFig. 10.7. Fig. 10.9 CIE chromaticitycoordinatesx andy andpaleness(luminosity,Y) calculated by the weightedordinatemethodfrom spectrasuchasthoseshownin Fig. 10.7. 210 Meat processing 10.14 Conclusion Thereare clearly manyways to obtain useful information for meat processing from on-line sensors, both in selectingcarcasses and in process control. The ready availability of software for multivariate analysisand neural networks makesit very tempting to adopt a strictly empirical approach– measuring a batchof knownsamples,thendeveloping a prediction equation for on-line use. This maybeunreliableif thereis anychangein the interactionbetween sample and apparatus, or in the natureof the samples evaluated. In the first category, simply moving the apparatus may necessitatea new prediction equation. In the second category, sampleswhose main variableis lipid content will not perform in thesameway assamplesdominatedby pH-relatedproteinfunctionality. The price of a trustworthy sensor is knowing how it works. Only then can the programmer anticipatethe unexpected. 10.15 Sourcesof furth er information and advice Furtherinformationonmeat sensorsmaybeobtained from Swatland(1995).For thoseworking with fibre-optic sensors, many of

the componentsand software conceptsarethesameasthose usedin microphotometry (Swatland,1998).Meat Scienceis the obvious journal to watch for further developments.My own on- goingstudiesusually appear in FoodResearchInternational which originatesin Canada. Fig. 10.10 Two extremesof gelatinisation– toughbeefperimysium(a) versus perimysiumfrom cookedturkey rolls with a crumbly texture(b). The optical path differenceof birefringence(nm) is affectedby thethicknessof thesample(sodifferences in absolutevalueof a versusb are irrelevant),but turkey sampleshowsearly gelatinisationstartingat 60ºCwhereasthe beef is unchangeduntil muchhigher temperatures. On-line monitoring of meatquality 211 10.16 References ABERLE E D, STADELMAN W J,ZACHARIAH G L andHAUGH C G (1971),‘Impedance of turkey muscle: relation to post mortem metabolites and tenderness’, Poultry Sci, 50, 743–746. 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The relation of browning intensity to chemical constituents andpH’, J Food Sci, 27, 177–181. PFÜTZNER H and FIALIK E (1982), ‘A new electrophysiological methodfor the rapiddetectionof exudative porcinemuscle’, Zbl VetmedA, 29, 637–645. 214 Meat processing RAY G B and PAFF G H (1930), ‘A spectrophotometric study of muscle hemoglobin’, Am J Physiol, 94, 521–528. ROME E (1967), ‘Light and x-ray diffraction studies of the filament lattice of glycerol-extractedrabbit psoasmuscle’, J Mol Biol, 27, 591–602. ROWAN A N andBATE SMITH E C (1939),‘Changesin the electricalresistance of muscleassociated with the onsetof rigor mortis’, Ann Rep Food Invest Board,London, 11–15. SALÉ P (1972),‘A ppareil de détectiondesviandesdécongeele´espar mesurede conductanceélectrique’, Bull Inst Internat Froid, Suppl, 2, 265–275. SCHMITTEN F, SCHEPERSK-H, JÜNGST H, REUL U and FESTERLING A (1984), ‘Fleischqualität beim Schweine. Untersuchungenzu deren Erfassung’, Fleischwirts, 64, 1238–1242. SEIDLER D, BARTNICK E andNOWAK B (1987), ‘PSE detection using a modified MS Tester compared with other measurementsof meat quality on the slaughterline’, in Tarrant P V, Eikelenboom G andMonin G, Evaluation and Control of Meat Quality in Pigs, pp 175–190,Martinus Nijhof, Dordrecht, Netherlands. SWANTEK P M, CRENSHAW J D, MARCHELLO M J and LUKASKI H C (1992), ‘Bioelectrical impedance: a nondestructive methodto determine fat-free massof live market swineandpork carcasses’, J Anim Sci, 70, 169–177. SWATLAND H J (1988), ‘Carotene reflectance and the yellowness of bovine adiposetissuemeasuredwith a portablefibreoptic spectrophotometer’,J Sci Food Agric, 46, 195–200. SWATLAND H J (1995), On-lineEvaluation of Meat, Technomic Press, Lancaster, Pennsylvania. SWATLAND H J (1996), ‘Effect of stretching pre-rigor muscle on the back- scatteringof polarized near-infrared’, Food ResInternat, 29, 445–449. SWATLAND H J (1998), ComputerOperation for MicroscopePhotometry, CRC Press,BocaRaton, Florida. SWATLAND H J (2000),‘Connective andadiposetissuedetection by simultaneous fluorescence and reflectancemeasurementswith an on-line meat probe’, Food ResInternat, 32, 749–757. SWATLAND H J and BARBUT S (1990), ‘Fibre-optic spectrophotometry for predicting lipid content, pH and processing loss of comminuted meat slurry. Internat J Food Sci Technol, 25, 519–526. SWATLAND H J and BARBUT S (1991), ‘Fluorimetry via a quartz-glassrod for predicting the skin contentandprocessingcharacteristics of poultry meat slurry’, Internat J Food Sci Technol, 26, 373–380. SWATLAND H J and BARBUT S (1995), ‘Optical prediction of processing characteristics of turkey meat using UV fluorescence and NIR birefringence’,Food ResInternat, 28, 325–330. SWATLAND H J and DUTSON T R

(1984), ‘Postmortem changes in someoptical, electrical and biochemical properties of electrically stimulated beef carcasses’, Can J Anim Sci, 64, 45–51. SWATLAND H J, GULLETT E, HORE T and BUTTENHAM S (1994), ‘UV fiberoptic On-line monitoring of meatquality 215 probe measurementsof connective tissue in beef correlated with taste panelscoresfor chewiness’,Food ResInternat, 28, 23– 30. TAPPEL A L (1957), ‘Reflectancespectral studiesof the hematinpigmentsof cookedbeef’, Food Res, 22, 404–407. TARLADGIS B G (1962), ‘Interpretation of the spectra of meat pigments. I. Cooked meats’, J Sci Food Agric, 13, 481–484. TØGERSENG, ISAKSSONT, NILSEN B N, BAKKER E A andHILDRUM K I (1999),‘On- line NIR analysisof fat, waterandprotein in industrial scalegroundmeat batches’, Meat Sci, 51, 97–102. WEBB N B, IVEY F J, CRAIG H B, JONES V A and MONROE R J (1970), ‘The measurementof emulsifying capacityby electricalresistance’, J FoodSci, 35, 501–504. WHITE J, KAUER J S, DICKINSON T A and WALT D R (1996), ‘Rapid analyte recognition in a devicebasedon opticalsensorsandtheolfactory system’, Anal Chem, 68, 2191–2202. YANO Y, MIYAGUCHI N, WATANAB E M, NAKAMURA T, YOUDOU T, MIYAI J,NUMATA M andASANO Y (1996a), ‘Monitoring of beefageing usinga two-line flow injection analysis biosensor consisting of putrescine and xanthine electrodes’,Food ResInternat, 28, 611–617. YANO Y, YOKOYAMA K and KARUBE I (1996b), ‘Evaluation of meat spoilage using a chemiluminescence-flow injection analysis system based on immobilized putrescine oxidase and a photodiode’, Lebens Wissens Technol, 29, 498–502. 216 Meat processing 11.1 Introduction This chapter describes the main microbiological hazards associated with meat and meat products. Meat is associated with a variety of pathogenic microorganisms some of which we are relatively familiar with. Worryingly, the past two decades has seen the emergence of ‘new’ microbial agents capable of causing disease. These recent developments and the continued increase in the number of cases of foodborne illness have resulted in widespread concern for consumer safety. Many of the recently emerging foodborne pathogens are associated with meat from poultry, cattle and other animals, and they do not necessarily cause overt signs of illness in these animals. The appearance of these pathogens is, generally speaking, a global trend and is not restricted to particular geographic locations. The reasons for their emergence and spread are poorly understood and it is suspected that the shift to a global economy, international trade, and changes in the livestock industry may have contributed to these recent developments. No doubt, some of this is also due to improved surveillance, reporting and methods of detection. The first principle of HACCP (conducting a hazard analysis) includes determination of the food safety hazards likely to occur and these may come from a variety of different sources. The list of hazards associated with meat and meat products includes protozoal parasites, helminths, arthropods, viruses, prions and bacteria, arguably the most important of these categories. Many bacteria are common inhabitants of animal intestines and their presence may be transient or long term. In addition to livestock being a source of infection, through internal carriage or hide contamination, pathogens may be introduced at any point in slaughter, processing, packaging, distribution and preparation of 11 Microbiological hazard identification in the meat industry P. J. McClure, Unilever Research, Sharnbrook food.Thebacteriaandmainprotozoal parasitesconsideredto behazardsin meat andmeatproducts arediscussed. Understandingthe origin of thesedifferent pathogensand their fate during processingis essentialfor control of thehazardsandmanagingtherisk posedby their presence. The analytical methodsusedto detectthe presenceof many of these pathogenshave advanced significantly in recentyears.Theseimprove- ments in detection and characterisation methodologies now allow for the trackingof differentpathogensthroughprocessing,enabling identificationof the origin of these agents.Thesedevelopments alsoallow links to bemadebetween apparently unrelated (e.g.sporadic) cases.The specificmethodologiesusedfor enumerationand detectionof particular pathogensare not within the scopeof thischapter,but thegeneralapproachesandrecent advanceswill bediscussed.A number of futuretrends li kely to impacton thehazardsassociatedwith meatand meat products arealsodiscussedin this chapter. Geneticevolution will continue to contribute to the appearance of new pathotypesor pathovars of microorgan- ismsandthis will result in pathogensthat possessnew combinations of known andunknown virulencefactors. 11.2 The main hazards 11.2.1 Salmonellae The genusSalmonella is subdivided into over 2000serotypes or serovars, based onuniqueantigenic structure. Furthersubdivision is possible through phage-and biotyping. Salmonellae are primarily intestinal parasitesof humansand many animals, including rodents,wild birds and domestic animals. Recently, the nomenclatureof salmonellaehasbeenrevisedsincemoderntaxonomic methods suggested that all serotypes of Salmonella probably belonged to one DNA- hybridisation group. S. enterica was originally subdivided into seven sub- groups, S. enterica subspp. enterica, salamae, arizonae, diarizonae, houtenae, bongori and indica. S.enterica subsppbongori has since been elevated to specieslevel. Only serotypesof subsp.enterica arestill named(e.g.S.enterica subsp. enterica serotype Typhimurium or S. Typhimurium or simply Typhimurium) indicating that the named serotype is a member of subsp. enterica. Although many salmonellae are potentially pathogenic in animals, the responseto infectionby thesameserotypein differentanimalsmaybedifferent. Althougha largenumber of serotypeshavebeenidentified, lessthan10%have beenisolatedfrom manandotheranimals. Salmonellaearemost often isolated from cattle andpoultry. Serotypesareclassifiedaseitherhostadaptedor non- host-adapted, depending on their host range and the majority show no host specificity. Host adaptedserotypesrarely causediseasein otherhosts.S.Dublin is traditionally host adaptedto cattlebut in some casehasshowna tendencyto spreadto swineandwasoriginally isolatedfrom achild. Thisserotypecancause severe disease(septicaemia, osteomyelitis,andmeningitis) in someindividuals. 218 Meat processing Salmonellosis in animals Generally speaking, younganimals are more susceptible to salmonellosis than older ones.There are a numberof factors that predispose animalsto clinical salmonellosis and these include poor sanitation, overcrowding, parturition, transportation and concurrent infections with other pathogens(e.g. parasites, viruses, etc).Many animals,particularly swineandpoultry arefed contaminated feed without developing any apparent clinical symptoms.Feed is usually contaminated through meat and bone meal, fish meal or soybeanmeal with organisms entering these materials during or after processing. Wild birds and rodents alsoprovide a sourceof contamination from faecescontaminating feed or buildings,andother possible sourcesincludecontaminatedpoultry litter and watercourses. Salmonellosis in cattleusually begins asan entericinfection, commencing with colonisation of theintestineandinvasionof theintestinalepithelium.This canbe followed by septicaemia, abortion,meningitis, pneumonia or arthritis, afterentryinto thebloodstream. Thetwo most importantserotypesin cattleare S.Typhimurium and S.Dublin. Typhimurium is foundworldwide andDublin is found mainly in Europe, westernUS andSouthAfrica. Antibiotic resistant strains of Dublin are now spreadingto the north-eastern US.1 Persistently sheddingcarrier animalsare thought to be the primary reservoirof Dublin, with most infections occurring when animalsare on pasture.Unlike Dublin, diseasecausedby Typhimurium is usually self-limiting, since persistent sheddersarenot thenorm. Typhimurium is knownfor primarily enteric disease stateswhereasDublin causesprimarily septicaemia. Themostimportant mode of transmissionfor Typhimurium is thefaecal-oral route.Both serotypescause seriousdiseasewith mortality rates sometimes as high as 50–75%. Other serotypesthat have causedinfection in cattle include Anatum, Montevideo, Newport andSaint-paul. In sheep, serotypes associated with diseaseinclude Abortus ovis, Dublin, MontevideoandTyphimurium. Infection in flocks resultsfrom introduction of infectedsheepand ingestion of the organism.Dublin and Typhimurium cause enteritis,septicaemiaandabortion, similar to the conditionsobserved in cattle. For sheepand goats, Typhimurium infection can come from a variety of environmentalandanimalsourceswhereas cattlearetheusualsource of Dublin. The serotypes most frequently associated with disease in pigs are Choleraesuis and Typhimurium and other serotypes that can causediseasein susceptible animalsincludeAnatum, Derby,Heidelberg, NewportandPanama. Choleraesuis causesparatyphoid, Dublin causes enteritis andmeningoencepha- litis and Typhimurium and other serotypes causeenteritis and septicaemia. Heidelberg canalsoproduceseverecatarrhalenterocolitis. In poultry, serotypes causing disease include Agona, Bareilly, Hadar, Oranienburg,Typhimurium, Gallinarum and Pullorum. The last two of these causefowl typhoid and bacillary white diarrhoea. Pullorum is now rarely isolatedin theUnitedStatesandnorthern Europe,dueto successful eradication programmes,but is of increasingimportance in Latin America, theMiddle East, Microbiological hazardidentification in the meat industry 219 the Pacific Rim, Africa and some partsof southern Europe. The incidence of Gallinarum has also beenreduced due to changes in husbandry and through eradication of Pullorum, with which it sharescommon antigens. In the areas where Pullorum has been eradicated, Typhimurium is often found, causing paratyphoid. Typical conditions of paratyphoid in poultry include enteritis, diarrhoeaandsepticaemia. During 1985/1986,S.Enteritidis PT4emerged asa ‘new’ problemin poultry in Europe. In 1993,thefirst outbreakof PT4occurredin theUS,andthenumber of isolations from eggsandthe farm environmentof laying flocks suggests that eggshavehada majorcontribution to thedramaticincrease in associatedhuman illness.Enteritidis is aninvasiveserotypeandhasachievedprominencebecause of its association with poultry eggs.Although eggshavebeenrecognisedasa sourceof infectionfor Typhimurium,theincidenceof foodpoisoningcasesfrom this sourcehasalwaysthought to havebeenlow. S. Typhimurium DT104 has recently emerged in cattle populations in particular parts of the world and causes severediarrhoea, with an associated mortality rate of 50–60%. Long-term carriage(up to 18 monthsfollowing an outbreak)hasbeenobserved in manyspeciesincluding cattle.2 Salmonellosisin man Non-typhoidal Salmonella spp.are one of the most commonly reported food- bornepathogensin industrialisedcountries.Symptoms of humansalmonellosis include nausea,vomiting, diarrhoea,abdominal crampsand fever, with illness lasting for 3–12 days.3 Associated clinical conditions also include reactive arthritis, Reiterssyndrome, septicarthritis andsepticaemia. Certain serotypes are being increasingly reported as the cause of salmonellosis. In 1989, Typhimurium, Enteritidis, Heidelberg,

Hadar and Agona accounted for 57.9% of all serotypes isolated from human infections and accounted for 46.5% of isolations obtainedfrom poultry, in the US. One serotype that hasincreasedsignificantly in recentyears is S.Enteritidis. Before 1990,Typhimurium wasthemost commoncauseof reported salmonellosisin a number of geographic regions. In 1990, this serotype was overtaken by Enteritidis and is now a major cause of human food poisoning in many countries.4 In recent years in the UK and westernEurope, the predominant phagetype responsible for egg-bornesalmonellosis is PT4 whereasin the US, although there is no predominant phage type associated with egg-borne infection, PT8 and PT13aare the most commonly isolatedphagetypes.5 The emergenceof other phagetypes,suchasPT6 in the UK, continuesto occur, as doesthe emergence of other typessuchas S. Typhimurium DT104, which is now appearing in Europe, north Americaandelsewhere.6 Themain reservoir of this pathogen,which often exhibits resistance to multiple antibiotics, is thought to be cattle, but therearereports of increasing incidence in poultry, sheep,pigs andgoats.This is in contrast to S. Enteritidis, which is mainly associatedwith eggsandpoultry. The invasivenessof DT104 in humansdoesnot appear to be anydifferentto othersalmonellae,butanincreasein occurrenceof severeillness 220 Meat processing has been reported, with higher proportions of those infected requiring hospitalisation. 11.2.2 Escherichia coli Like salmonellae, theprimary habitat of E. coli is theintestinaltractof manand otherwarm-bloodedanimals.Many E. coli arecommensalorganismsandcause no harmbut there aresome typesthat arepathogenicto manandotheranimals andthese arenot regardedaspartof thenormalflora of thehuman intestine. E. coli is also commonly found in externalenvironments(e.g.soil andwater)that havebeenaffectedby humanandanimalactivity. E. coli is divided into more than170serogroupsbasedon thesomatic(O) antigens,andover50 flagellar (H) and 100 capsular (K) antigens allow further subdivi sion into serotypes. Serogrouping and serotyping are used with biotyping, phage typing and enterotoxin production to distinguishstrains able to causeinfectious diseasein manandanimals. Therearemany typesof diseasecaused by E. coli andthesedependon the virulence factors present. The known virulence factors include adhesins and colonisation mechanisms, haemolysin, ability to invade epithelial cells and production of a number of toxins including heatlabile enterotoxins,heatstable enterotoxins, cytotoxic necrotising factors andverocytotoxins(or Shigatoxins, Stx1 and 2). The adhesionand colonisation factors include fimbrae, haema- glutinnins and specific adhesins suchas the F4 (K88) antigen. The encoding genesof theseand other virulence factors may be carried on transmissible plasmidsor on the chromosome. Thereare currently six recognised virulence groups comprising enteropathogenic E. coli (EPEC), enterotoxigenic E. coli (ETEC), enteroinvasiveE. coli (EIEC), verotoxigenic E. coli (VTEC or Shiga- like toxin producing E. coli or SLTEC, which include enterohaemorrhagic E. coli or EHEC), enteroaggregativeE. coli (EAggEC) anddiffuselyadherentE. coli (DAEC). Disease in animals E. coli infectionsoccurfrequently in manyfarm animals, includingpoultry.7,8 In youngeranimals,there areprincipally two typesof diseasewhich aresystematic colibacillosis, causedby a range of O-serogroupsand enteric colibacillosis, causedby a few host-specific enteropathogenic strains.In olderanimals, a third groupof diseases,causedby a numberof O-serogroups,causesmastitis in cows and sows.Other, sporadic infections, suchasurinary tract infections,can also occur. Enteric colibacillosis involves oral infection, followed by site specific adhesion to intestinal mucosa,allowing colonisationandreleaseof toxins,which causesdamageto intestinal cells or other organs. Colibacillary diarrhoeais an acutediseaseandoccurs mostfrequentlyin calves,lambsandpiglets,soonafter birth andis mainly caused by ETEC.TheOK groupsin calvesandlambstendto be thesame,whilst theOK groupsassociatedwith pigsarerarely isolatedfrom Microbiological hazardidentification in the meat industry 221 other species. In cattle, commonserotypesinclude O8, O9 andO101. In pigs, the most common serotypeis O149 and other commonly isolated serotypes includeO8, O138, O147andO157.Thereappears to havebeenlittle changein the serotypesthat causecolibacillary diarrhoea or their virulence factors, in recent years. Other forms of entericcolibacillosis arecolibacillary toxaemia in pigs, associated with a few serotypes that causeshock in weanersydrome, haemorrhagic colitis andoedema disease.Theseformsof diseasearethoughtto relate to production of enterotoxin, endotoxin or a neurotoxin. Systemic colibacillosis is causedby invasive strains and involves their survival and multiplication in extra-intestinal sites.This occurs frequently in calves, lamb and poultry, but not in pigs, and develops by passageof E. coli from the alimentaryor respiratory mucosato the bloodstream.From there,a localised infection, such as meningitis or arthritis in calves and lambs or air sacculitis andpericarditis in poultry, or a generalisedinfection(colisepticaemia) can develop. O78 and O2 are commonly isolated from poultry, and these serotypesarerarelyobservedin human isolates.Strainscausingcolibacillosis in calvesbelongto relatively few serotypessuchasO15:K,O35:K,O137:K79,and O78:K80.The lastof theseis themostfrequently isolatedandis alsoassociated with similar conditionsin lambsandpoultry. Bovine mastitisis still an important diseaseandcanrangefrom mild forms, which causeclots, milk discolorationandudderswelling, to severe illness that canresult in deathof the affectedanimal.Mastitis is caused by a largenumber of serotypes that are not easily distinguishedfrom strains in normal faeces. Endotoxinandnecrotising cytotoxin arethought to play significant rolesin this disease. It is generally thought that VTEC do not causeovert diseasein animals,but thereis increasingevidenceof illnesscaused by someVTEC in neonatal calves andolderanimals.9,10Bovine VTEC strainssharemany of thevirulencemarkers with VTEC strains causing infection in man, but in Germany, the intimin- positive strains(thosestrainscausingattaching andeffacinglesions,encoded by the eaegene)arethought to be restrictedto the stx1 genotype, only capable of producing Stx1. In Brazil, however, a recentstudyhasshownthat 60% of the VTEC strainsisolatedfrom cattlepossessbothstx1 andstx2. SerogroupsO5 and O118aremainly associatedwith diseasein calves,serogroupsO26, O103and O111causediseasein calvesandhumans,but O157is generally considered to be carriedby healthyanimalsandonly associatedwith diseasein humans. Disease in man Worldwide,the importanceof diarrhoealandother diseasescausedby E. coli is immense,particularly in children in developing countries. In developed countries, the incidence of foodborne illness associated with E. coli is also significant andappears to be increasing. More worryingly, recentyears have seen the emergence of particularly virulent E. coli, suchasE. coli O157:H7 (the predominant VTEC serotype), that are able to causeserious illness in man, with low infectious doses, e.g. fewer than 100 cells. The severity of 222 Meat processing disease caused by VTEC can vary from asymptomatic carriage to haemorrhagic colitis (HC), to life-threatening conditions suchashaemolytic uraemic syndrome (HUS) in children and thrombotic thrombocytopaenic purpura(TTP) in adults.HUS is themostcommon causeof acuterenalfailure in children. For the other pathotypesof E. coli, suchas EPEC,ETEC and EIEC, clinical studies suggest that more than 105 EPEC are necessary to produce diarrhoea,108 ETEC are necessaryfor infection and diarrhoeaand 108 EIEC are required to producediarrhoeal symptoms in healthy adults. EPECcausea bloody diarrhoeain infants(commonly referredto asinfantile diarrhoea),which in somecases maybeprolonged;ETEC causeself-limiting diarrhoea,vomiting andfever, andtravellers’ diarrhoea;EIEC causeshigella- like dysentery;EAggECcausepersistent diarrhoeain children, particularly in developing countries; andDAEC causechildhood diarrhoea. EventhoughtherearemanyE. coli responsiblefor diseasein animals,most of the E. coli pathogenic in man are not the same as those causingillness in animals.Indeed,the principal reservoir for many humanpathogenic E. coli is believed to be man. However, this is not true of VTEC, including E. coli O157:H7, where the main reservoirs are thought to be cattle and other ruminants.11 Dairy cattle, particularly young animalswithin herds,havebeen identified asa reservoirof E. coli O157:H7 andother VTEC, andthis serotype hasalso beenisolatedfrom otherruminantssuchassheepandgoats.Henceraw foodsof bovineor ovineorigin arelikely to bevehiclesof E. coli O157:H7 and other VTEC through faecal contamination during slaughter or milking procedures. In one survey,four per cent of cattle were contaminatedprior to slaughter, andafter processing,30%of the carcasseswerecontaminated.12 The most frequently implicated vehicle of infection for E. coli O157:H7 is undercookedgroundbeef. Surveys of raw meatsfor sale haverevealed E. coli O157:H7 in 2–4% of ground beef, 1.5% of pork and poultry, and 2% of lamb.13,14 Other studies suggest contamination rates for VTEC in someraw foodsof between 16 and40%.The incidenceof E. coli O157:H7-relatedillness is worldwide. Humaninfectionswith VTEC O157:H7areundernationwide surveillance in a numberof countries, but detection of other non-O157VTEC types is more difficul t andperformedonly by specialist laboratories.Humansarelikely to be more exposed to non-O157VTEC becausethesestrains aremore prevalentin animals and as contaminants in foods. The growing number of non-O157 serogroups associatedwith human diseasenow includeO26,O103, O111, O118 and O145.15 It is thought that both horizontal gene transfer and intragenic combination are important for evolution of VTEC. Particular regionsof the globeshowpatterns of emergencethat appear to be unique, e.g.20–25%of E. coli O157 isolates in Germanyare sorbitol +ve. The most commonnon-O157 serotypes in GermanyareO26:Hÿ, O103:Hÿ, O111:Hÿ andO145. In Italy, the HUS casescaused by O26 strainsnow outnumber thosecausedby O157:H7. Studiesin animalsdemonstratethatsomeof these serogroups, suchasO118,are alsoprevalent in farm animals, andarea likely reservoir. Microbiological hazardidentification in the meat industry 223 Humanpathogenicstrainsof VTEC vary in their ability to causeillness,and this depends on virulence attributes and other unknown factors.16 Pathogenic VTEC O26, O103and O111 belongto their own lineagesand possessunique profiles of virulencedeterminantsthataredifferent from thevirulenceprofile of E. coli O157:H7, which is said to contain a more complete repertoire of virulence traits. This may explain why E. coli O157:H7 is the predominant VTEC serotype. One of the problemsthat is becoming increasingly recognised is that the terminologyusedto describe diarrhoeagenic E. coli is complex andby no means definitive. Since it was first recognisedthat E. coli could causediarrhoea, an array of virulencefactors havebeendiscoveredanda number of categoriesof diarrhoeagenic E. coli havebeenproposed,generally basedon the

presenceof non-overlappingvirulencefactors.However,EPECstrainsandEHECstrainsare often regroupedunder the nameof attaching/effacing E. coli (AEEC) on the basis of the ability to produce commonattaching and effacing lesionsin their hosts. Therearealreadya number of documentedstudiesdescribing isolatesthatdo not fit neatly into any of the recognisedcategories of diarrhoeagenic E. coli. This should not besurprising consideringthat thevirulencefactors areencoded on ‘pathogenicity islands’ , bacteriophage, transposons and transmissible plasmids. Some of theseelements havealso beenfound in other members of theEnterobacteriaceae. Therefore,we shouldanticipate that therewill beother combinationsof known and currently unknown virulencefactorsappearing in the group of organisms we currently call E. coli, and other members of the Enterobacteriaceae. 11.2.3 Campylobacter jejuni C. jejuni wasnot recognisedasa causeof humanillnessuntil the late1970sbut is now regardedas the leading cause of bacterial foodborne infection in developedcountries.17 It is oneof 20 speciesandsub-specieswithin the genus Campylobacter and family Campylobacteriaceae, which also includes four species in the genusArcobacter. Despitethe huge number of C. jejuni cases currently being reported, the organism does not generally trigger the same degree of concern asE. coli or salmonellae, sinceit rarely causes deathand is rarely associatedwith newsworthy outbreaks of food poisoning. It is amongthe most common causes of sporadic bacterial foodborne illness. C. jejuni is associatedwith warm-bloodedanimals,but unlike salmonellaeandE. coli does not survive well outside the host. C. jejuni is susceptible to environmental conditions and does not survive well in food and is, therefore, fortunately relatively easyto control. Food associated illness usually results from eating foods that are re-contaminatedafter cooking or eating foods of animal origin that are raw or inadequately cooked. The organism is part of the normal intestinal flora of a wide variety of wild anddomestic animals,andhasa high level of association with poultry.18 The virulenceof the organism, assuggested 224 Meat processing by the relatively low infectious doseof a few hundred cells andits widespread prevalencein animals,areimportantfeatureswhich explainwhy this relatively sensitive organismis a leadingcauseof gastroenteritis in man. Campylobacteriosis in animals C. jejuni is a commensalorganismof the intestinal tract of a wide variety of animals.19 In cattle, younganimals aremore oftencolonisedthanolderanimals, and feedlot cattle are more likely to be carriers than grazing animals. Colonisation of dairy herdshas beenassociated with drinking unchlorinated water.Day-old chickscanbe colonised with asfew as35 organisms,andmost chickensin commercial operations are colonised by four weeks. Reservoirsin the poultry environmentincludeinsects,unchlorinateddrinking waterandfarm workers, but probably not feeds, since theseare thought to be too dry for survival of campylobacters. It hasbeenproposedthat C. jejuni is a causeof winter dysentery in calvesandolder cattle,andexperimentally infected calves have shown some clinical signs of diseasesuch as diarrhoeaand sporadic dysentery. Nevertheless,the aetiologyof naturally occurring diseasein animals remainsunconfirmed. C. jejuni is, however,a known causeof bovinemastitis, and the organisms associatedwith this condition have beenshown to cause gastroenteritis in personsconsuming unpasteurisedmilk from affectedanimals. Othercampylobacters,suchasC. fetus, areknown to causeabortionsin sheep andcattle andsomestrainsof C. sputorumareknown to causeporcineintestinal adenomatosis and regional ileitis in pigs, but theseappearto be host-specific diseases. Campylobacteriosis in man C. jejuni and C. coli are the most common campylobacters associatedwith diarrhoeal diseasein man and are clinically indistinguishable. Also, most laboratories do not attempt to distinguish between the two organisms.It is thought thatC. coli constitute 5–10%of cases reported ascausedby C. jejuni in the US. Campylobacteriosis in man is usually characterisedby an acute,self- limit ing enterocolitis, lasting up to a week. A small proportion (5–10%) of affectedindividuals suffer relapses.Symptomsof diseaseoften include fever, abdominal pain anddiarrhoea,which may be inflammatory, with slimy/bloody stools,or non-inflammatory,with watery stoolsandabsenceof blood. Reactive arthritis andbacteraemiaarerarecomplicationsandinfection is also associated with Guillain-Barré syndrome, an autoimmune peripheralneuropathy causing limb weakness. This condition is thought to be associated with particular serotypes (e.g.O:19, O:4 andO:1) capable of producing structuresthat mimic ganglioside motor neurons. Thereare a number of pathogenicity determinants that havebeensuggested for C. jejuni, including motility, adherence,invasion andtoxin production, but little is known aboutthemechanismcausingdiseasein man. There is considerable evidence that poultry is the main vehicle for transmitting Campylobacter enteritis in man.Poultry typically haspopulations Microbiological hazardidentification in the meat industry 225 of 104–108 C. jejuni per gram of intestinal content and more than 75% of chickens and turkey often carry the organism in their intestinal tract. It is estimatedthat 30% of retail poultry is contaminatedwith C. jejuni at levelsof 102–104 per gram. Also, serotypesassociated with poultry are also frequently associatedwith illnessin humans. Prior to 1991, Arcobacter butzleri and A. cryaerophilus were known as aerotolerant Campylobacter. These organisms have been associated with abortions and enteritis in animalsand enteritis in man.Although both species areknown to causediseasein man,most humanisolatescomefrom thespecies A. butzleri. Thereis very little knownabouttheepidemiology,pathogenesis and real clinical significanceof Arcobacters,but it is thought that consumption of contaminatedfood mayplay a role in transmissionof this groupof organismsto man. Although Arcobacters have never been associated with outbreaks of foodborne illness, they have been isolated from domestic animals, poultry, groundpork andwater. 11.2.4 Yersinia enterocolitica Surveillance datasuggestthat Yersinia enterocolitica is an increasingcauseof gastroenteritisin man in Europeand the US.20 The main causeof yersiniosis during the 1970sand 1980swas thought to be milk and the main serotype associatedwith diseasewasO:8. Sincethen,O:3 hasbecomethe predominant serotype in developedcountries.The main reservoir of this serotypeandother important serotypes, such as O:9, is pigs and consumption of pork is an important risk factor for infection. Y. enterocolitica is a component of the intestinal flora of redmeatanimals,particularly pigs. Poultry is known to carry significant levelsof yersinias.Although meatandmeatproductsfrom goatsand sheephaveneverbeenimplicated in outbreaks of foodborne yersiniosis, small ruminantscanharbour the pathogen. Y. enterocolitica causesgastroenteritis in manandcanalso causepersistent arthritis. Infection doesnot, however, alwaysresult in diarrhoea.Yersiniosis is usually characterised by abdominal pain, accompaniedby fever, with or without diarrhoea. Because of its ability to multiply at refrigeration temperatures, Y. enterocolitica is of specialinterest to particular areasof thefood industry. There is relatively little known aboutthe mechanisms of pathogenicity but the genes for invasion of mammaliancells lie on thechromosomeandall theother known pathogenicity determinantsare found on a plasmid. The other member of this genusthatcancausegastroenteritis is Y.pseudotuberculosisandlargeoutbreaks of gastroenteritis causedby this organism havebeenreported in Japan. Disease associated with Y. pseudotuberculosis resembles typhoid and is often fatal. Y. enterocolitica is not known to causediseasein animals.Y. pseudotuberculosis is rarely associated with infections in cattle and sheep, with those in cattle manifesting aspneumonia or abortion. 226 Meat processing 11.2.5 Staphylococcusaureus Meat or meat productsare not thought to be a major sourceof S. aureus infectionin maneventhoughS.aureusis animportantpathogenin animals.The principle sourceof transmissionbetweenanimalsandmanis unpasteurisedmilk and cheesemade from unpasteurised milk. Outbreaksof staphylococcal food poisoning in man are frequently associated with improper food handling and temperatureabuseof foodsof animalorigin, but it is generally believed that the mainsourceof contaminationis foodhandlers.Nevertheless, strainsof S.aureus can becomeendemic in food processingplants and meatcan be contaminated from animalor humansources.S.aureushasbeenisolatedfrom cattlecarcasses and is also found in raw beef. There is a high correlationbetweencoagulase production and production of enterotoxins, of which there are at least seven heat-stable typesassociatedwith food poisoning. In animals,S.aureuscauses a number of differentdiseases.The mostrelevant diseasefor transmission of the organism to manis bovine andovine mastitis. 11.2.6 Listeria monocytogenes Listeriosis is an atypical foodborne diseasethat has attracteda great deal of attention sincethe early 1980s mainly because of the severity,high mortality rate and non-enteric nature of the disease. Listeriosis is caused by L. monocytogenes, which is found in many environmentsandis frequentlycarried in theintestinal tractof many animals,includingman.L. monocytogenes is often found in healthy animals andhumans, with a carrier rate of 10–50%in cattle, poultry andswine.The organism hasbeenisolatedfrom a variety of foods, at levelsof 13%in raw meat,3– 4%raw milk and3–4%of dairy products.21 Some of the major outbreaks in man havebeenattributedto meatproducts suchas pork tongueandmeatpaté. Foodsassociatedwith outbreaks havelargely been refrigerated, processedand are ready-to-eat. The diseasein man is commonly associated with meningitis, septicaemia and abortion. Recent outbreaks, however, havebeenassociated with a milder form of diseasecharacterised by gastroenteritis and flu-like symptoms. In these recentoutbreaks, serogroup1/2 has been implicated whereasmany of the humanstrains isolated previously belongto serovar4b andto onemajor ribovar.Serogroup1/2 accountsfor most of thefood andenvironmentalisolatesandtogether,serotypes 1/2a,1/2band4b account for up to 96% of the isolatesin man. Host factors arelikely to play an important role in the susceptibility to listeriosis, together with presenceof virulence factors in the organism. Many individuals frequently ingest L. monocytogenes without any apparent ill effects.Although listeriosis is a severe disease, thenumberof cases,comparedto some of theotherfoodbornediseases, is relatively low. SinceL. monocytogenes is widely distributedin soil, vegetationand faeces, most animalsare exposed to it during their lifetime. L. monocytogenes is also commonly foundin largenumbersin poor-quality silage, andruminantsfed this material are more likely to develop listeriosis. As in humans, predisposing Microbiological hazardidentification in the meat industry 227 factors are importantfor diseasein animals. The clinical conditionsassociated with animallisteriosisaresimilar to thehuman disease,andincludesepticaemia, abortion, enteritis and meningoencepahalitis. Interestingly, the isolates asso- ciated with processed meats more often originate from the processing environmentthanfrom the animal itself. 11.2.7 Clostridium

perfringens Strains of C. perfringensare classified into 5 types, A–E, according to the extracellulartoxinsthatareformed.TypeA is responsible for almostall casesof foodbornediseasein humans.Type C very rarely causesfoodbornediseaseand results in necrotic enteritis, but is only a concern in individuals who are nutritionally impairedor whoseintestinalproteolyticenzymeactivity is reduced. TypeA C. perfringensis usuallypresentin thesoil atconcentrationsof 103–104/g. Theothertypesareobligateparasitesof domesticanimalsanddonotpersistin the soil. TypeA strainsoccurwidely in raw andprocessedfoods,but at numberstoo low to causeinfection.Theorganism is foundin thealimentarytractof nearlyall speciesof warm-bloodedanimals. C. perfringens is primarily associatedwith outbreaks of food poisoning involving handling problemsandmeat, meatproductsandpoultry arefrequently implicated in outbreaks. Illness usually results from ingestion of heavily contaminatedfood and typical symptomsare diarrhoeaand severeabdominal pain. Occasionalreportsof illnesswithin 2h of ingestion indicateingestion of preformed toxin. Sporulation of ingested bacteria is also associated with production of enterotoxin, which is destroyed by heating(e.g.60ºC for 10 min). In animals,type A causesyellow lamb diseasein sheepanda similar illness (toxin producedin thesmall intestine) in goats.TypeB is known to causelamb dysentery, and haemorrhagic dysentery in sheep,goats and calves. Type C causesenterotoxaemia in a varietyof animalspeciesandtypeD causesthesame disease,but apparentlyonly in sheep. TypeE is believed to causehaemorrhagic necrotic enteritis in calves. 11.2.8 Clostridium botulinum Strains of C. botulinumareclassified into several types(A–G) depending on the antigenic propertiesof the toxin produced.TypesA, B, E andF areresponsible for most casesof humanbotulism, whereastypes C and D causeillness in animals. The outbreaksof foodbornebotulism associated with meats, suchas home-curedhams, tendto occurmainly in Germany,France, Poland andItaly. The incidenceof foodborne botulism is extremely low, but the severity of diseaseandits heatresistancemeanthat it is the targetmicroorganismof many preservationprocessesusedfor foods.Sporesof C. botulinumarepresent in the soil andenvironment, but to a lesserextentthanC. perfringens. Sporesmay be present in meat, but this is usually at levels between0.1–10 spores/kg. The diseasein man is an intoxication and causesgeneralweaknessof limbs and 228 Meat processing respiratory muscles,andoften nauseaandvomiting. Like humans,botulism in animals almost always arises from ingestion of food contaminated with preformed toxin. Thereis evidencethat animals carry sporesandthis may lead to internal contamination andcontamination of meatprocessingenvironments. In Europe, occurrenceof spores is generally infrequentbutwhen it occurs, levels canreach 7/kg of samplewhereas incidence in meats in the US is muchlower, probably reflecting the incidence of meat-associatedbotulism in the two areas. 11.2.9 Other bacteria Other bacteria associatedwith meat animals include brucellae (e.g. Brucella melitensis) andBacillusanthracis, whichcancausediseasein manbutareregarded asa relatively low risk from meatandmeatproducts.B. cereus is a ubiquitous organismandhasbeenfound in raw beefandmilk, andthe organismis directly linked to dairy cows, being incriminated in abortionsand mastitis. Therefore, contaminationof carcassesof dairycowsis possiblebut is not thoughtto constitute a significantrisk in foodsof animalorigin. Foodborneillnesscausedby B. cereus generally results from improper handling of foods. Other organisms,such as Corynebacteriumpseudotuberculosis, MycobacteriumparatuberculosisandPas- teurellaspp.areresponsiblefor diseasesin animalsandhavebeenlinkedto disease in humansbut transmissibilityfrom animalsto manhasyet to beproven. 11.2.10 Parasites Giardia duodenalis and G. lamblia G. duodenalis is oneof the most commonprotozoal infections in man,causing diarrhoeal disease in infants and young children, in both industrialised and developing countries. The parasiteis also found in many domestic animals including cattle,sheepandgoats,particularly younganimals.Thereis evidence of zoonotic transmission,but themajor sourcesof contamination arethought to be wateror food contaminatedwith water that hasbeenin contactwith faecal material.22 Cryptosporidium parvum C. parvumhasa wide spectrum of animal hosts,including cattle, goats, other farm animals andman. It is an intracellular parasitic protozoan responsiblefor self-limiting diarrhoeal il lness in its hosts.23 Symptoms include watery diarrhoea, nausea, anorexia, abdominal cramps, fever and weight loss. The life-cycle is completedwithin one host and large numbersof oocystsare then transmitted, in faeces,to the environment, where they may survive for long periodsof time. In man,if individualsareyoungor immunocompromised,more seriousgastroenteritiscanoccurandthis canbefatal. In diarrhoetic younggoats and sheep, there is a high prevalence of C. parvum, suggesting a strong association between infectionanddisease.In surveyslooking for presenceof C. Microbiological hazardidentification in the meat industry 229 parvum in animals, oocystswere found in calvesat levels of up to 22% of animals tested. The reservoirsandroutesof transmissionsuggest that meatand meat productsmay be a sourceof infection in humans.Sausageandtripe have beenshown to containC. parvumoocysts.23 Contaminatedwateris known to be thecauseof largeoutbreaks of disease.Poor diagnosisof diseasein manandthe small numbersof oocysts (100s) necessary to causeinfection mean that many cases of cryptospordiosismay go undetected. Other parasites Toxoplasmagondii is a protozoal parasite well known for causingabortionsin sheep. Theorganismis alsoknown to causeacuteprimary infection in manand is a particular risk to pregnant women.Consumption of raw or undercooked mutton is thoughtto be responsible for transmission to man. Trichinellaspiralis is reponsiblefor trichinellosis,which,in man, beginsasan acute gastrointestinalcondition andis followedby fever andmyalgias.Chronic illness may result since 10–20% of casesdevelop neurologic or cardiac symptoms.Illnessin manresultsfrom consumption of rawor undercooked pork, wild boaror horsemeat, with mostcasesoccurringin Europe. Taeniasaginata also causesoutbreaksof diseasein Europethroughconsumption of infectedbeef. Cyclosporaspp.causevery similar diseaseto C. parvumandarealsosimilar in otherrespectssuchasbiology andpathogenesis,but thereis only onespecies, Cyclospora cayetanensis, known to causeillness in man. This speciesis not known to haveanyotheranimalhost.Othermembers of thegenuscausedisease in other animals. Echinococcusgranulosusis anotherparasitethatcancauseinfection in man. The larval stage is foundin sheep,goats,cattle,pigsandman. Thefinal hostfor the parasiteis the dog. Contamination of meatis not thought to occurdirectly; the main routeof infection is throughcontamination of eggsfrom dogs. 11.2.11 Other agents Transmissiblespongiform encephalopathies(TSEs) Scrapie hasbeenprevalent in sheepandgoats in particularpartsof theworld for many years.This diseaseis regardedastheprototypeof TSEs, foundin humans andother animals. TheseTSEscauseprogressive degenerative disordersof the nervous systemandresult in death.Thereis no doubt that theseare infectious diseasesbut the nature of the infectious agentsremains elusive.Theoriesabout the causative agentvary and there is continuous debateaboutthe presenceof nucleic acids and the importance of a protease resistantprotein (prion theory), derived from a normalhostprotein. In the early 1980s,an epidemic of bovine spongiform encephalopathy (BSE) began in the UK, and the recycling of infectedcattle material is thought to havecontinueddriving this epidemic. The recentemergenceof a new variantof Creutzfeldt-Jakobdisease(vCJD) in humansin theUK hasled to thebelief that this newdisorderis relatedto the 230 Meat processing transmissible agentcausingBSE. The working hypothesisis that transmission hasoccurred throughcontaminated material entering the food chain. This, in turn, has focusedattention back on scrapieas a potential sourceof infection, despitethe fact that large quantities of contaminated material must havebeen consumedwithout any apparent ill effects. It is not known how many vCJD casesare likely to emergeasa consequenceof the BSE epidemic and thereis still much to learnaboutall aspectsof this groupof diseases. Viruses Virusesarenot generally consideredto betransmittedto manvia meatandmeat products, althoughcaliciviruses infect humansand other animals.Within the family Caliciviridae, thereare four distinct genera comprising vesiviruses and lagoviruses,which containa broadrangeof animal virusesand Norwalk-like viruses(NLV or smallroundstructured viruses) andSapporo-like viruses, which until recently haveonly beenassociatedwith man.NLVs arethemain causeof gastrointestinal illness in restaurantsand institutions.Recent datasuggest that NLV infections oftenoccurin calvesandsometimesin pigs.24 Thesignificance of this recentfinding is unknownat the presenttime. 11.3 Analytical methods This sectionof the chapterprovidesa brief overview of the typesof methods availablefor detectionof foodbornepathogens.Detaileddescription of methods for eachof thepathogensdiscussedabovearenot included.Conventionalmethods for the detectionand characterisationof bacteriaassociated with foods rely on specific media. Thesemethodstend to be relatively cheap, sensitiveand can provide both quantitativeand qualitative information. However, they can be lengthy procedures,are labour intensive, rely on multiplication of the target organismanddo not usegeneticinformation,which canbe usedto discriminate betweenclosely relatedorganisms. Nevertheless, there have beenadvancesin recentyearsthat facilitate someof theseconventionalproceduressuch as the introduction of chromogenicor fluorogenic media, removing the need to do further sub-culturingand biochemicalsteps.Modifications to particular media havealso beenmade to improve performanceand cut down someof the other stepsinvolved in conventionalculture methods.Other improvements include availability of automatedcolonycounting,usingimageanalysis,andavailability of automatedbiochemicalidentificationsystems.Theseadvancesprovideresults directlycomparableto conventional testsbutmaketesting muchmoreconvenient. Relianceon particular methodsfor the detectionof pathogenscan lead to problems where atypical typesor responsesare evident. For example, E. coli O157:H7 isolatesareroutinely distinguishedfrom otherE. coli becauseof their inability to ferment sorbitol. This meansthat sorbitol +ve E. coli O157:H7 strains,suchas thosefound in Germany, would go undetectedduring routine testing.Selective media,becauseof their inclusion of inhibitory agents,may Microbiological hazardidentification in the meat industry 231 also underestimatetargetorganismsif they areinjured. In suchcases, inclusion of a recovery stageis critical to the detection procedure. Alternativeapproachesfor thedetectionof specific microorganismshavealso beendeveloped in recentyearsandtheseincludeflow cytometry, impedimetry, immunological techniquesandnucleic acid basedassays. Flow cytometry is an optically-based approach that can detect low numbers of cells (e.g. 102–103 bacteria) rapidly (within

minutes), but food matrices can interfere with the techniqueand distinction betweenlive and ‘dead’ cells can be problematic. It has been used for the enumeration of viruses in water and is also used to enumerateCryptosporidiumoocysts. Impedimetry is basedon changes in the electrical conductivity of liquid mediacausedby growth of the targetorganism. Althoughthis methodis not ‘rapid’, it is convenient for high throughputsinceit is full y automated and can deal with multiple samples simultaneously. Specificity is dependenton the mediausedto grow the targetorganisms. Immunological methodsarebasedon the specificbinding of an antibodyto anantigen. Theadventof monoclonalantibodiesnow providesa consistentand reliable source of characterised antibodies. Immunoassaysare divided into homogeneous and heterogeneousassays. There is no need for markers with homogeneous assays,sincetheantibody-antigencomplex is directly measurable and the test time is short. Examples of this type of assay are agglutination reactions, immunodiffusion and turbidimetry, and testsare availablefor most pathogens. Heterogeneous assays are more complex procedures and use immobilised antibodies on a variety of supports and reportingsystems.These precedurescanbecarriedout without theneedfor specialequipment.Detection limit s arebetween103–105 cell/ml for most pathogens.Direct detection in foods is not possible and enrichment is required. Immunoassayscan also detect bacterial toxins. Automated immunoassays are also now commercially available. Developments in genetically-based techniquesin recentyearsprovidea step- changein analytical capability for detection andcharacterisation of pathogens. Thesetechniquesarebasedon the hybridisationof targetDNA or RNA with a specific DNA probe.Thespecificity of this probeis dependenton its nucleotide sequence.When hybridisation hasoccurred, detection can be via a numberof methods, similar to thoseusedin immunoassays.Commercial assaysare now availablefor a number of pathogens. Thedetectionlimit for bacteriais 103 cells, so enrichment is sometimesrequired. Alternatively, an amplification stepmay beused.Examplesof this arepolymerasechainreaction, involving denaturation of the targetDNA and annealing of primersto the single strand,followed by extensionof theprimersusinga thermostablepolymerase, or RNA amplification through the concerted action of enzymes(NASBAÕ). Use of amplification methodsrequirescleansamples,andavailability of commercial kits nowenables routine laboratoriesto carry out procedureswhich until recently wereregarded as complex and only carried out in specialist laboratories. Becausethese methodsare basedon geneticelements, resultsonly indicate the potential to produce toxin or expressvirulence.Therearealsoproblemswith falsepositives 232 Meat processing (e.g. ‘dead’ cells) and negatives (polymerase inhibitors or accessibility to the targetorganism). Molecular typing is alsopossible now, allowing identification to sub-species level, aidingepidemiological andtaxonomic studies.Thesetechniquesareoften referredto as fingerprinting methods. They include restriction fragmentlength polymorphism (RFLP), random amplified polymorphic DNA (RAPD), pulsed field gel electrophoresis(PFGE) andAFLPÕ which combinesPCRandRFLP. Whilst conventional methodsstill have an important role to play, molecular methodsare likely to becomemore commonly used.The next breakthroughin diagnostic methodology is likely to come from ‘DNA chip’ technology, which combines semiconductor manufacturing with molecular techniques. This technology will allow rapid and cheapanalysis of multiple sequences,using large arrays of nucleotides, making it possible to detect and type different organisms in the samefood sample. Thereare,however, significant hurdles to be overcome,with virusesandparasitesposingtheir own particular problems. 11.4 Future trends Foodborne pathogensthat have emerged in recent years sharea number of characteristics.Nearly all of these havean animal reservoir from which they spreadto man, i.e. theyarefoodbornezoonoses,butunlikeestablishedzoonoses, theydo not oftencauseillnessin theanimalhost.Anotherworrying trendis that thesepathogensareableto spreadglobally in ashortperiodof time.Manyof the emerging pathogensare becoming increasingly resistant to antibiotics and this hasbeenattributed, partly, to the useof antibioticsin animals. The practice of usingantibioticsin animalproduction is comingunderincreasing pressureand therehavebeenrecent legislative changes that address this issue in particular partsof the world. Unfortunately,it is likely that someof thesepracticeswill continuein thoseareas that arenot properly regulated or policed. New food vehicleshavebeenidentified in recentyears. Thesenew vehicles includefoodsthatwereoncethought to be‘safe’ suchaseggs,applejuice, fresh fruit, fresh vegetables and fermented meats. With consumer preferencesfor fresher, less heavily processedfoods likely to continue, it is possible that new food vehicles for foodborne diseasewill continue to emerge. Alternative processes, if incorrectly assessed, may also provide an additional sourceof infection. Continuedconsolidationwithin the food industry is likely to lead to increasingly largemarketsandwider distribution from centralisedmanufactur- ing operations. With increasing demand from increasing populations, we are likely to seemorereuseandrecyclingof waterandwaste,andthis mayhavean impacton the microbiological hazardswe haveto face. Fortunately, improved epidemiological capability, provided through better detection methods and better cooperation/coordination between different surveillance networks, is likely to allow quicker detection of geographically widespreadoutbreaks of foodborne disease.Molecular methodsare transform- Microbiological hazardidentification in the meat industry 233 ing taxonomyandour understandingof thegenomesof particular pathogensand groupsof pathogens, suchas the Enterobacteriaceae. This hasalreadylet us gain some insight into evolutionary processes and should allow us to better anticipatethe potentialof microorganismsto incorporatenew genetic material anddevelopnewvirulencecharacteristics.Betterunderstanding of pathogenesis of foodbornediseaseandcolonisationof animalsmayalsoallow developmentof new interventionstrategies. With anticipatedincreasesin the averagelife expectancy,throughimproved medical treatmentof chronic diseaseandotheradvances,thereis likely to be an increase in theproportionof personswith age-relatedsusceptibility to foodborne disease.Also, there is likely to be a continuing increasein the number of immuno-suppressedindividuals,due to infection with HIV and other chronic illnesses. At thepresenttime we areseeinga decreasein thenumberof casesof some commonfoodbornepathogens,suchassalmonellae,in developedcountries like the US, UK and other partsof Europe. This is encouraging and suggeststhat some diseaseprevention strategiesmaybebeginning to takeeffect.Despitethis, the incidence of foodborne illnessesand deathscaused by unsafe food are increasing. The geneticplasticity of the microorganismsposesa seriousthreat for the future, andwill undoubtedly lead to the emergenceof novel infectious diseases.At the genetic and molecular level, the virulencetraits of pathogens clearly showusthatpathogenicitydoesnot ariseby slow adaptiveevolution but ratherby stepchanges. 11.5 Sourcesof further information and advice General articles describing members of the Enterobacteriaceae, such as salmonellae,E. coli andY. enterocolitica areavailable.3,20 Enterobacteriaceae andE. coli infections in animalshavebeenreviewed in a number of articles.7,8 Specific articles describing foodborne listeriosis, campylobacteriosis and the emergenceof E. coli O157:H7 arealsoavailable.11,18,21Foodborneparasitesare reviewed in severalarticles.22,23,25 A review of analytical methodsused in microbiology hasbeenpublishedrecently.26 11.6 References 1. McDONOUGH P L, FOGELMAN D, HIN S J, BRUNNER M A and LEIN D H, ‘Salmonella enterica serotype Dublin infection: an emerging infectious diseasefor theNortheasternUnitedStates’,J Clin Micro, 1999 372418–27. 2. BARLEY J P, ‘S.typhimuriumDT104in cattlein theUK’, VetRec, 14075. 3. D’AOUST J, ‘Salmonellaspecies’ in FoodMicrobiology– fundamentalsand frontiers, ASM Press,Washington, 129–58,1997. 4. RODRIGUE D C, TAUXE R V and ROWE B, ‘International increase in 234 Meat processing Salmonella enteritidis: a new pandemic?’ Epid Inf, 1990105 21–7. 5. MISHU B, KOEHLERJ,LEE L A, RODRIGUE D, BRENNER F H andBLAKE P et al., ‘Outbreaksof Salmonella enteritidis infections in theUnitedStates,1985– 1991’, J Inf Dis, 1994169 547–52. 6. CENTERSFOR DISEASE CONTROL AND PREVENTION, ‘Mult i-drug resistant Salmonella serotypeTyphimurium– United States’,Mor Mort Wkly Rep, 199747 308–10. 7. LINTON A H andHINTON M H, ‘Enterobacteriaceaeassociatedwith animals in healthanddisease’, J App Bact SymSupp, 198871S-85S. 8. WRAY C andWOODWARD M J, ‘Escherichiacoli infections in farm animals’ in Escherichia coli: mechanismsof virulence, edSUSSMANM 1997,49–84. 9. DEAN-NYSTROM E A, BOSWORTH B T and MOON H W, ‘Pathogenesis of O157:H7 Escherichia coli in neonatal calves’ in Mechanisms in the Pathogenesisof Enteric Diseases, Plenum Press,New York, 47– 51,1997. 10. PEARSONG R, BAZELEY K J,JONESJ R, GUMMING R F, GREENM J,COOKSONA andWOODWARD M J, ‘Attaching andeffacinglesionsin the largeintestine of an eight-month-old heifer associated with Escherichia coli O26 infection in a groupof animalswith dysentery’, Vet Rec, 199925 370–2. 11. ARMSTRONG G L, HOLLINGSWORTH J andMORRISJ G, ‘Emerging foodborne pathogens: E. coli O157:H7 asamodelof entryof anewpathogeninto the food supply of the developedworld’, Epid Rev, 199618 29–51. 12. CHAPMAN P A, WRIGHT D J, NORMAN P, FOX J and CRICK E, ‘Cattle as a possible source of verocytotoxin-producing Escherichia coli O157:H7 infections in man’, Epid Inf, 1993111 439–47. 13. DOYLE M P and SCHOENIJ L, ‘Isolation of Escerichia coli O157:H7 from retail freshmeatsandpoultry’, Appl Env Micro, 1987 53 2394–6. 14. SEKLA L, MILLEY D, STACKIW W, SISLER J, DREW J and SARGENT D, ‘Verotoxin-producing Escherichia coli in groundbeef – Manitoba’, Can Dis Weekly Rep, 199016 103–5. 15. WORLD HEALTH ORGANISATION, ‘Report on a WHO working group meeting on shiga-like toxin producing Escherichia coli (SLTEC) with emphasison zoonotic aspects’,Bergammo, Italy, Rep no WHO/CDS/ VPH/94.136,1994. 16. NATARO J P and KAPER J B, ‘D iarrheagenic Escherichia coli’, Clin Rev Micro, 199634 2812–14. 17. TAUXE R V, ‘Emerging foodborne diseases: an evolving public health challenge’, EmerInfect Dis, 19973 425–34. 18. KETLEY J M, ‘Pathogenesisof entericinfection by Campylobacter’, Micro, 1997143 5–21. 19. STERNN J andKAZMI S U, ‘Campylobacter jejuni’ in Foodborne Bacterial Pathogens, Marcel Dekker, New York, 71–110,1989. 20. OSTROFFS ‘Yersinia as an emerging infection: Epidemiologic aspectsof yersiniosis’, Contrib Micro Immunol, 199513 5–10. 21. FARBER J M and PETERKIN P I, ‘Listeria monocytogenes, a foodborne pathogen’, Micro Rev, 199155 476–511. Microbiological hazardidentification in the meat industry 235

pathogen’, Micro Rev, 199155 476–511. Microbiological hazardidentification in the meat industry 235 22. TREESA J ,‘Zoonotic protozoa’, J Med Micro, 199746 20–4. 23. HOSKIN J C and WRIGHT R E, ‘Cryptosporidium: an emerging concern for the food industry’, J Food Prot, 199154 53–7. 24. VAN DER POEL W H M, VINJÉ J, VAN DER HEIDE R, HERRERA M-I VIVO A and KOOPMANSM PG, ‘Norwalk-like calicivirus genesin farm animals’, Emerg Inf Dis, 2000 6 (1). 25. GOODGAME R W, ‘Understanding intestinal spore-forming protozoa: cryptosporidia, microsporidia, isospora and cyclospora’, Ann Intern Med, 1996124 429–41. 26. DE BOER E and BEUMER R R, ‘Methodology for detection and typing of foodborne microorganisms’, Int J Food Micro, 199950 119–30. 236 Meat processing Part III New techniques for improving quality 12.1 Introduction This chapter refers to computer models that simulate beef cattle production. Such models consist of mathematical equations and instructions which mimic the roles, interactions and influences of the various inputs to beef cattle production. The chapter recognises that modelling is a term which refers to both building and using models, and that beef cattle production includes the complex interactions between the physical environment, financial environment, management, feed supply, and animal reproduction and growth. The chapter considers the challenge faced by model builders in dealing with such complexity, overviews possible applications, and gives an example of a simple beef production model. Pasture and animal scientists started to model beef cattle production after computers first became available for research in the 1960s. A rapid expansion in the range, scope and role of models followed in response to the even more rapid expansions in the power and accessibility of computers. Insight into the progress and philosophy of modelling pasture and animal production are obtained from recent reviews.1, 2 Models have been a valuable aid to research, extension, and management at the farm, industry or government levels because of the following three attributes. 1. If each equation in a model is regarded as a hypothesis pertaining to a specific process or component, then a model can be regarded as a collection of hypotheses, derived from past research that can be further modified and developed through new research. In this way, a model becomes a repository for past research and a precursor for future research.3, 4 Model construction is now a common activity that gives research direction and focus. 12 Modelling beef cattle production to improve quality K. G. Rickert, University of Queensland, Gatton 2. Models provide a quantitative description of the many interacting components which may have conflicting responsesin a beef production system.4 This is a powerful and uniqueattribute that greatly exceeds the analytical capacityof the human mind. For example with beef cattle, as stocking rate increases (the number of animals per unit areaof land), the liveweight and value per animal decrease,variable costs increase and productionper hectareat first increases and then decreases.5 A manager must balancethe trade-offs betweenprofit, risk, pasture degradation and premium prices.6 Similar trade-offs between productivity, stability and sustainability arecommonin farming systems7 anda model allowsusersto experience ‘virtual’ reality in managing grazing systems. 3. Models can give a quantitative extrapolation in space and time of information derivedfrom pastresearch and experiences.For example,by processinghistorical recordsof daily weather data, estimatesof variability in output can be expressed as probability distributions.8 Similarly, by processingthe historical weather for different land units in a region, and thereby estimating spatial and temporal variations in forage production, estimatesof safestocking ratescan be comparedagainsttrendsin actual regionalstocking ratesto indicateperiodsof overgrazing.9 Further, if the spatialmodelusescurrentweatherdataas input, the output is a nearreal- time display of pastureand/or animal production10 that can influence government or industrypolicies.All of these applicationsrely on a model’s ability to extrapolate information in temporal and spatialdimensions, and this attribute is fundamental to the role of modelsin information transfer.11 Today a wide range of models on different aspectsof plant and animal production are being used as aids to research, farm management, and to determine governmentor industry policies.1 12.2 Elementsof beef cattle production Beef cattleproduction deals with the conversion of climatic andedaphic inputs into plant products, which areconsumedby various classesof animals in a beef cattle herd to give meat for humanconsumption. This beef production system consistsof four interacting biophysical andbioeconomicsubsystems,which are manipulated through the management subsystem in response to the climate subsystem (Fig. 12.1).Thestructureandsignificanceof the varioussubsystems aredescribed in moredetail below. The climate subsystem is largely outside the managementsubsystem but it directly affects the four subsystems influenced by a manager. For example, rainfall supplies soil water for plant growth, may causesoil erosion, and influences the rate of waste decomposition in soil. Further, prevailing temperature,humidity and radiation influenceplant growth, and the incidence of plantandanimalpestsanddiseases.Climatic inputsalsodisplayseasonaland 240 Meat processing year-by-yearvariations anda managermust devisestrategiesto copewith these variations. Indeed, matching the farming systemto the level andvariability of climate inputs is a big challengefor a farm manager.12 Seasonal variations in climate give rise to seasonalvariations in quality andtypeof foragewhich may trigger fodder conservation (e.g. hay) to offset periodsof forage deficiency. Wide year-by-yearvariations in climate inputs,often expressedasdroughts or floods which lead to major perturbations in foragesupply and market prices, needto be handledthroughskillful and resourceful management.13 However, long-term weather forecasts now give managersprior warningof likely climatic extremes.For example, in northern Australia seasonalforecasts indicate the probability of rainfall in the forthcoming three to six months exceeding the historical medianvalue, therebypermittingmanagersto makeanearly response to a likely distribution of rainfall.14 Also extremely hot or cold temperaturescan causedeathsin plants and animals, and computer models such as GRAZ- PLAN,15 coupled to weekly weather forecasts,give early warning of likely mortalities in susceptible classesof animals.In bothcases, recentimprovements in the reliability and skill of weather forecastingare helping farmersto cope with wide variations in climate. The land subsystem supplies water and nutrientsfor plant growth. Since it includes many of the ecological processes that sustain the whole system, both the managerand interest groupsin the wider community are keento keepthe Fig. 12.1 Interrelationshipsbetweenbiophysicalandbioeconomicsubsystems (rectangles)with the managementsubsystemof the farmer.The biophysicaland bioeconomicsubsystemscontainprocessesthat determinetheir status.The interface betweentwo subsystems(arrows)representsa conversionof materialsinto a new form. Themanageris constantlyrespondingto theclimatesubsystem,which impactsto varying degreeson the soil, pasture,animalandeconomicsubsystems. Modelling beefcattle production to improvequality 241 land subsystem in good condition. Land degradation through soil erosion, desertification, salinisation, acidificationandnutrient declineis a majorconcern in many of the world’s grazing landsand has led to the notion of landscape management. With thisapproach,managersin a regionwith acommonattribute, such as a river catchment, are encouraged to adopt strategies that enhance sustainable development rather than exploitation of the land subsystem. Landscapemanagementalso recognises that grazing lands produce food as well as ecosystemservices, suchas water and biodiversity that are needed to sustain thecitieswhere mostpeopleli ve. Preferredmanagementstrategiesfor a landscapemay arise throughdifferent managementoptionsbeing assessedby government agenciesor local communities, and computer models are often useful tools in this process.16 Plantswithin the foragesubsystemsupplydigestiblenutrientswhengrazedby cattle. Forageaccumulatesthroughplant growth and foragenot eaten,together with faecesandurinefrom cattle,returnto thesoil subsystemthroughthedetritus food chain.Thequality of forageon offer varieswith thegrowingconditionsand typeof plantspeciesin thesystem.New growthis themostdigestibleandthereis a steadydecline in quality as plant partsage,die and senesce.Sincetemperate grasseshave a higher digestibility than tropical grasses,grazing systemsin temperatezonestend to display higher animal performancethan tropical zones, Leguminousspeciestendto havehigherdigestibility thangramineousspecies.17 If a grazingsystemis basedon sown pasturesthe managermay selectto grow a mixedpasturewhich usually consistsof a few speciesthat are well suitedto a particular situation. This contrastswith native rangelandswhere the system consistsof manydifferent species,often including trees.Herea manageraimsto keepthepasturein goodconditionby maintainingadequateplantcoverto reduce soil erosion and a predominanceof desirable rather than undesirableplant species.18 In bothsownpastureproductionsystemsandnativerangelands,forage condition and animal performancecan be manipulatedby managementoptions such as the choice of stocking rate, type and amountof fertiliser application, periodsof grazingandconservation,level of supplementaryfeeding,and fire in the caseof rangelands.19,20 The cattle subsystem producesanimals for sale through the processes of reproductionand growth within a herd consisting of different animal classes. The number of differentanimalclasseson a farm largely dependson thequality of the pasturesubsystem and on the objectives of a manager. In essence, breeding cows produce calves and after weaning these move into different classesastheygrow andage(Table12.1).Usually youngfemalecattle(heifers) areselectedto replaceagedor culledcowsandarematedfor thefirst time when they reach maturity and a specific weight that depends on the breed and prevailing nutrition. Undergoodnutrition, heifers may be matedfirst at 15–18 months of age,but with the poorer nutrition in extensive rangelands,mating usually takesplace at 24–30months.Heifersthat arenot requiredfor replacing cowsmight besoldfor slaughteror for breedingpurposeselsewhere.Male cattle are commonly castrated before weaning although a small number of high- 242 Meat processing performing males may be retained to replaceaged bulls. Depending on the prevailing nutrition and markets, male cattle may be retained for one to three years after weaning, to be sold for slaughter or for finishing elsewhereon anotherfarm or in a feedlot. Thus,which marketto target,andhow the cattle shouldbe fed to meet the market, are key strategic decisionsfor a manager. Deciding when to sell specific groupsof cattle is a key tactical decision for a manager. The different classesof cattle in a beef herd have different nutritional requirementsbecausethey differ in weight andage.The term adult equivalent

(AE) relatesthe energy requirement of differentclassesto a common base,the energyrequirementfor maintenanceof an adult animal,suchasa non-lactating cow. The AEs of Table12.1 canbe determined from feedingtablesbut a first approximation for growing cattle is given by: AEˆ LW0:75=105:7 …12:1† Table 12.1 Classesof cattlecommonlyfound in beefcattleherdsin extensivegrazing systems.Adult equivalent,being the ratio of the energyrequirementof a classto the energyrequirementof an adult animal, is a coefficient for equatinganimal numbersin eachclassto a commonbase.Intensivegrazingsystemswith a higher level of nutrition will havefewer classessincecattlearesold at a youngerage Animal class Adult Age Comments equivalent years Cowsand 1.3 2–12 Managersaim to havebreedingcowscalve calves annually.Calvesareusuallyweanedat about6 monthsof age. Yearling 0.55 0.5–1.5 Heifersare femalesthat havenot hadonecalf. heifers Whenmatureat 1.5 to 2.5 years,dependingon 2-year-old 0.75 1.5–2.5 breedandgrowing conditions,somearemated heifers to replaceculled cows.Surplusheifersmay be sold for slaughteror asbreedingstock. Yearling 0.55 0.5–1.5 Steers,or castratedmales,aresold for finishing steers elsewhere,or for slaughter.Age andweight at 2-year-old 0.8 1.5–2.5 saledependson thelevel of nutrition theyexperi- steers ence,the specificationsof availablemarkets,and 3-year-old 1.0 2.5–3.5 on the price advantageof different markets. steers Within limits setby prevailingclimatic and 4-year-old 1.1 3.5–4.5 economicconditions,a managercantargeta steers specificmarketby manipulatingfeedsuppliesin the pasturesubsytem. Culled cows 1.0 3–12 Cowsno longersuitablefor breedingdueto age or infertility. Usually conditionedandsold for slaughter. Bulls 1.1 3–7 Male animalsfor matingwith cows.Onebull is requiredfor every20 to 25 cows. Modelling beefcattle production to improvequality 243 where LW andLW0.75 are the liveweight andmetabolic weight of animalsin a specific classand105.7is themetabolic weightof a non-lactatingbovine with a liveweight of 500kg/head.21 Themarketsubsystemrefersto thedifferentmarkets for beefcattleavailable to a manageralong with the prices and profit margins associated with each market. Specificationsfor marketsvary with location.In an extremecasethere is no specification, andall cattle aresold asbeefwith no separationof cutsat retail outlets.At theother extreme,individualanimalsarepreparedfor aspecific market and tracedthrough the supply chain, with carcasses being gradedfor quality and various cuts of meat separated and sold at prices that reflect consumer preferencesandthegrade. Farmersin countriesthatexport beef, such asUSA, Australia,CanadaandNew Zealand,commonly havea rangeof market options that arespecified in termsof age,gender,weight andfat thicknessof a carcass.However, the classificationschemeis not standardisedinternationally, although there is an international trend to reduce the allowable limit s for residuesof pesticideandgrowthpromotantsin exportbeef.Penaltiesfor farmers in not meetingspecificationsfor chemical residues areusually severe,including condemnationof all meatin the caseof excesschemical residues. 12.3 Challengesfor modellers The abovedescriptionof beef production is deceptively simple. In practicea model builder is facedwith thechallengeof expressing thecomplex interactions between components of the system (Fig. 12.1).Specific challengesinclude • how to match the primary purpose of the model to the most appropriate structure • how to handle natural variability in the biophysical components and the interfacebetweenthe subsystems,and • how to validatethe completedmodel. Answers to thesequestions are interrelated and reflect back to the history and philosophyof model building. 12.3.1 Matching purpose and structure Models of beefproduction systemsarecommonly built asaidsto research, farm managementor policy evaluation and their structure may be mechanistic, empirical or a combination of both.1 Empirical models estimate outputs by empirical equations developed from experimental observation of output in relation to oneor more influencingvariables,while mechanistic models reflect a theoretical understanding of the factorsthat control outputs. The relativemerits of mechanistic andempirical structures havebeenhotly debatedandthe choice of structureis a critical andoften difficult decision for a model builder.2,4,22,23 Mechanisticmodels, becauseof their strongertheoretical base,tendto be more 244 Meat processing versatile and are more likely to explain responsesthan empirical models, but theymaynot bemore accurate andoftencontainparameters thataredifficul t to determine in practical situations.Conversely, the robustnessof an empirical model depends on the rangeof experimental data usedin its derivation, and spuriousresults might occur if it is applied outside this range.Thus model builders shouldspecify the derivation and application of an empirical model, and users should adhere to thesespecifications.As a variation on the above distinction, some models combine both empirical and mechanistic elements, such as an empirical model being used to processand interpret the results previously storedfrom manysimulationexperiments with a mechanisticmodel. Researchmodelsarebuilt by researchersto analysethecomplex interactions in beef production systems. They can be regardedas a repository for past research sincethey collate and integrate informationfrom pastresearch.They are also a precursor for future research since gaps in knowledge and understandingare highlighted. Because research models focus on processes andtheir interactions,theyareoftenmechanistic in structureandhavea limit ed distribution. However, GRAZE is an exception to this statement, being a comprehensivemechanistic model of forageand animal growth that is widely distributed andwell documented.24 Sometimesa researchmodel evolvesinto a management or policy model, therebyreducingdevelopmentcosts. Models for farm managementare usually designedto evaluatemanagement options pertaining to one or more components of the system. They aid management by evaluating different scenarios thereby allowing preferred strategiesto be identified, but importantly, a manageris freeto acceptor reject the output. Developingthis type of modelrequiresconsiderable time andeffort, since to be acceptedby potential users, the packageneedsto operate in a convenientandreliablemanner,haveahighdegreeof validity or skill, andhavea commercialarrangementfor distributionandafter-salesservice.1 FEEDMAN25 is an example of many commercialdecisionsupport systemsthat focus on farm management.However,history suggeststhat experiencedfarmersdo not readily usesuchsoftwarefor commonroutinedecisionsunlessits useis clearlybeneficial and it is promotedby a trusted product champion.26–28 On the other hand, professionalfarm advisors who are paid to recommendpreferredmanagement optionsarelikely to usethesoftwareto justify arecommendation.Becauseafarm advisormayhavemanyclients,decisionsupport softwarethatis regularlyusedby a few farm advisorsmay still have a big impact on farm management.Both mechanisticandempiricalsub-modelsarewidely usedin managementsoftware. Policy modelsservegovernmentor industryleadersby estimatingoutcomesto possiblescenariosand initiatives in policy. Both mechanisticandempirical submodelsare usedin policy modelsdealing with pastureand animal production. Policy models range from those that provide a one-off analysisof a specific problemto thosethatprovidea regularongoingservice.An exampleof a one-off analysisthat influencedpolicy wasthe rejectionof a plan,basedon resultsfrom field researchover ten years,to constructfarm damsandusethe storedwater to irrigate crops to improve the forage supply in north western Queensland. Modelling beefcattle production to improvequality 245 Simulationstudiesbasedon long-termrecordsof climateshowedthattheplanwas not viable becauserainfall was too variable.29 Apparently the field study that supportedthe plan coincidedwith a run of high-rainfall years.An exampleof a regularongoingserviceis themonthlymapsof relativepastureyield, adjustedfor prevailing stocking rates,which are derived from a pastureproductionmodel operatingon a 5 5km grid for the Stateof Queensland.30 The mapsprovidean objectiveassessmentof droughtstatusfor governmentandindustry.Constructing and maintaining a policy model of this scale requiresan integratedteam of scientists,programmersandsupportstaff. As with managementmodels,a policy model’scredibility dependson its scientific baseandvalidity. 12.3.2 Coping with linkagesbetweencomponents With regard to Fig. 12.1, the statusof eachsubsystem is expressed by several differentterms,which reflect thepurpose of theoverallmodelandthestructure of the sub-models that simulate each subsystem. Since the subsystems are interdependent, they needto be linked in an appropriate manner,an issuein model building that is often called the interfaceproblem. As an illustration, simple expressionsof the statusof eachsubsystem might be: 1. climate subsystem – inputs of solar radiationand/or temperatureon plant growth andrainfall on soil watersupply; 2. land subsystem – amount of soil water (mm) available for plant growth in responseto daily rainfall runoff, drainageandevapotranspiration; 3. pasturesubsystem – yield (kg/ha)of leaf andstem,potentially for eachplant speciesin the pasture,in responseto daily plant growth lessconsumption andsenescence; 4. animalsubsystem – liveweight (kg/head)of eachanimalclass,in response to an initial liveweight andaccumulateddaily liveweight gain; and 5. economic subsystem – farm profit ($ or $/ha) in response to value of animalssold less variable costs. Interfacebetween climate, land and pasturesubsystems Mechanistic modelsoften estimate plant growth as the productof intercepted solar radiation and radiation use efficiency. Interceptedradiation dependson leaf areaof the forage,and radiationuseefficiency links the soil and climate subsystems,being dependent on prevailing climate,soil nutrient statusandsoil water supply.31 In practice,radiation interception and radiation useefficiency aredifficul t to simulatein pasturesin rangelandsthatareamixtureof C3andC4 speciesgrowingasspacedplantsundertreesin asemi-aridenvironment,andare grazed selectively by cattle. Under these complex circumstancesan empirical model basedon field observations can be a useful tool. For example, pasture growth (PGkg/ha)canbe estimated as: PGˆWUE WU …12:2† 246 Meat processing whereWUE is wateruseefficiency,anotherterm that links the two subsystems for aspecified site(kg/mm), andWU is wateruseoveraspecifiedtime step(e.g. mm/day). Equation(12.2)avoidsthe difficul ties associatedwith radiation interception by recognisingthestrongdirect relationshipbetween waterusevia transpiration and foragegrowth via photosynthesis,two gaseous transfer processes that are controlled by leaf stomata.It can be appliedat different temporaland spatial scales.32 On a daily time step, WUEbecomestranspiration efficiencyandWU is daily transpiration estimatedby a sub-model of soil water balance, but on monthly or seasonaltime step, WUE becomesrainfall use efficiency and effective rainfall (actual rainfall less runoff) is an approximation of WU. AlthoughWUE varieswith fertilit y statusof thesoil, seasonalconditionsandthe numberof treespresent, it is aparameter thatcanbedeterminedsimply for asite from measurementsof plantgrowthin relation to WU.

TheFEEDMAN decision support systemestimatesmonthly plant growth throughthis approach and the defaultvaluesof WUE for manydifferentsoil-forage combinations wereeither obtained from field experiments or by integrating output from a daily plant growth model. In either case,the default values can be customised to reflect local conditions. Interfacebetweenpastureand animal subsystems This interface must account for nutritional demands of different classesof animals,all of which havetheability to moveandselecta preferreddiet from a pasturethat exhibitswide spatial andtemporalvariation in yield andquality. In mechanistic terms,animalproduction is dependenton intakeof digestible nutrients, and once the amount and quality of diet is known, models for estimating different forms of production (e.g. liveweight change, milk production, wool growth) in different animal classesalreadyexist.33 Thus the interfaceproblem becomes how to estimate, either directly or indirectly, two interdependentterms, the amount (intake) and quality (digestibility) of diet. Actual intakeis usuallyless thana potential intake,which depends on thebreed and liveweight of animals, due to constraints arising from the amount and quality of forageon offer. Foragedigestibility declineswith age,is greaterin leaf than stem, and varies across species. Mechanistic models commonly simulatediet selectionby partitioning theforageonoffer into digestibility or age categorieswith animals thenselectingprogressivelyfrom high to low categories until their appetite is satisfied.34 Whilst this approach tends to mimic diet selectionin temperate pastures reasonably well, the descriptive functions are essentially empirical relationshipsderivedfrom field experiments.Theapproach has been less successful in rangelands with a more heterogeneousbotanical composition andswardstructure.35 However, a morerealistic algorithmfor diet selectionin heterogeneousforagesplaces plant speciesinto broad preference categories (e.g. preferred,desirable, undesirable, toxic, emergency and non- consumed) and then computesthe proportion of eachpreference classin the Modelling beefcattle production to improvequality 247 diet.36 Thealgorithmassumesthatananimalhasexperiencewith thevegetation, and has learned to avoid toxic species and non-consumed species. The ‘emergency’category accountsfor speciesthatareonly eatenafterthepreferred, desirableandundesirable speciesaredepleted. The above ‘mechanistic’ models are essentiall y based on ‘empirical’ expressionsderivedfrom diet selectionstudieswith parametersthat are rather abstract and site specific.To avoid thesedifficul ties, the FEEDMAN package usedthenotionof potentialliveweightgainto characterisetheseasonalvariation quality of different forages.Potential liveweight gain is the monthly liveweight gainof a standard animal(a 200kg cross-bredsteer,Bostaurusby Bosindicus) grazing the forageat a low stocking rate in a goodseason.It is a bioassayfor forage quality that canbe measured,but more importantly, it is meaningful to farmersand can be adjusted to reflect local experience and knowledge.With potential li veweightgain for a standardanimalgiven, the energy concentration of the forage can be estimatedand applied to different animal classes,after taking account of the impact of high stocking rate on reducing intake anddry conditions reducing foragequality.25 Because this approachusesa bioassayto characterise forage quality, and a mechanistic model to estimate animal performance, it canbe readily adapted to herdsof different species, breedsand classesof livestock. Interfacebetween animal and economic subsystems Operating profit of a beefcattleenterprise on a farm is given by: Gross profitˆNumber sold…Animal valueÿVariable costs†…$† …12:3† where Number_sold is thenumber of animalssold, Animal_valueis theaverage value of saleanimals,Variable_costsareaveragevariable or operatingcostsper animalassociatedwith different managementoptions.Comparison of the gross profit for differentmanagementoptionsindicatestherelative profitability of the options. Estimation of Variable_costs is a simple arithmeticexercise,but sincethere is wide variation in local costs,a modelmust allow a userto modify andrecall this information, and a usermust updatethe information as required. On the other hand,estimation of Animal_valueis a twostepprocesswhereanimals are first allocated to a market category (if more than one exists), each with a corresponding sale price that usually exhibits spatial and temporal variation. Thus,tablesof marketpricesfor usein thecalculationof Animal_valueneedto beupdatedregularly. Thedeterminationof marketcategoriesis locationspecific since there is wide national and international variation in the title and specificationsfor eachcategory. In countrieswith well developedbeefmarkets, categoriesmaybespecifiedby age,sexandbreedof cattle,by weightexpressed as liveweight or carcassweight, and by an indication of the degreeof ‘finish’ expressedas a condition score in live cattle or fat thickness for carcasses. However, markets are not necessarily mutually exclusive in that while a 248 Meat processing premium market may have narrow specifications,cattle suited to a premium marketmay alsobe suitedto a lower-priced market with wider specifications. Mechanistic modelsattemptto estimate animal growth and development,and the associated fat deposition.37,38 Condition scorehasbeenderivedempirically from the history and statusof animal performance,39 but neitherapproachhas beenapplied to a full rangeof marketspecifications.FEEDMAN usesa simple approach to estimateAnimal_value in that the characteristics of eachherd are compared againstentriesin a tableof markets,specifiedin termsof monthlysale price,andbreed, age,classandliveweightof cattle.The highestprice matchis thenselectedandusedto calculateAnimal_value. 12.3.3 Coping with natural variability On-farm complexity Creating a ‘user friendly’ presentationof software that mimics pastureand animalproduction ona farm is achallengebecauseamultidimensionalscenario must be described through a keyboard and monitor. The multi-dimensional scenario might consistof descriptionsof fields in thefarm,pasturesin thefields, number andclassof animalsin herds,grazingmanagementof herds,andperiod, type, and amount of supplementaryfeeding (Fig. 12.1). In addition, potential userscommonly prefer the software to have keystrokes and a screen layout similar to otherfamiliar software.Also, outputsmust beclear,easilyunderstood, and suitable for further analysis or storage. One approach used by model builders to meettheserequirementsis to consult with a panelof potential users on a regular basis and progressively modify the software in responseto suggestions from the panel.11 Such ‘ interactive prototyping’ is a time- consuming task that can lead to major changesin the layout of screensfor entering data and displaying results, but experience has shown that model builders, who know a package intimately, are not expertsin ‘user friendly’ presentations.In practice,therearetradeoffs between thecapacity of a decision support package to handlewide variations in farm productionsystemsand the needfor the package to be ‘user friendly’. Extensive help notes, default values for input parameters,andtrainingexercisesandexamplesall assista noviceuser in mastering a package. In addition to complexity due to on-farm variations mentionedabove,climateandpricesareoff-farm inputsthatdisplaywidespatial andtemporal variations. Climate In the caseof climate a usermay wish to evaluatemanagementoptionsover a range of seasonal conditions contained in historical records of climate. One approach is to useall historical dataasan input and thenexpresskey outputs, suchas farm profit, asa probability distribution. Anotherapproach is to usea probability distribution of historical annual rainfall to establish categoriesof ‘seasons’ that reflect natural variations,suchas: Modelling beefcattle production to improvequality 249 very dry, rainfall likely to be lessthanthis category in 10% of years; dry, rainfall likely to be lessthanthis category in 30% of years; median, rainfall likely to be lessthanthis category in 50% of years; wet, rainfall likely to be lessthanthis category in 70% of years; and very wet, rainfall likely to be lessthanthis category in 90% of years. The formerapproachdemandsaccessto a largedatabaseof historical recordsof climate,particularly if amodel is to apply to awide rangeof locations,eachwith a different climate history. The secondapproach, to select from the same comprehensive databasea relatively small numberof typical climatecategories for each location, thereby eliminates the need for regular access to a large database of historical records. Both approaches are an attempt to assess managementoptionssimulatedby themodel in termsof therisk or likelihood of certain outcomes.This is akeyattributeof modelsof beefproduction in variable climates,which is notobtainedby usingaverageor medianclimatedata. Indeed, if only medianclimate datais used,animalproduction at high stocking ratesis overestimated becauseyear-by-yearvariations andinteractionsare ignored.8 In addition to analysing historical records of climate, model users are frequentlyinterestedin evaluatingmanagementoptionsin relationto thecurrent statusof cattle andforageon a farm andfuture climatescenarios that arebased on long-termweatherforecasts.13 Currently long-term weather forecastsindicate the probability of rainfall in the next threeor six monthsbeingaboveor below median rainfall, and the skill of the forecasts is improving.40 To caterfor this requirement,modelsmust allow usersto enterpotential future rainfall. 12.3.4 Verifica tion and validation Model verification ensures that the computer programs on which a model is basedare free of ‘bugs’ andperformproperly within specific limi ts. Usually a model builder usesspecialinput dataand parameters to test componentsof a model and their interactions undera wide rangeof operating conditions. The program needsto be correctedif valuesof the variousvariablesandprocesses exceed an acceptable range. Problems may arisefrom a flaw in the algorithm describing a process,particularly as upper or lower limit s are approached,or from a typing error in the program code. A sensitivity analysis is another componentof verification that indicatesthe relative importance of accuracyin model inputs. Here a simulation experiment is designedto test the relative sensitivity of inputsandparametersthat influencea system.Obviouslyaccuracy is more important with sensitive than with insensitive inputs. The relative sensitivity of different inputs is indicatedby comparing the changein output caused by a specificchangein thedifferent inputs (e.g.percentchangein output after a 5, 10 or 20% changein an input parameter). Whilst verification is primarily the responsibility of model builders, simple exerciseson theselines give model users a good appreciation of the operation and limit ations of a model. 250 Meat processing Model validationrefersto how well a modelmimics the systemit is meantto represent.Validation is commonlydemonstratedby first instructinga model to mimic a wide rangeof scenariosthat havebeenactually observed,and then by comparingpredictionsfrom a modelagainsttheobservations.Thevalidationdata shouldbe independentof thedatausedin developinga model.Linear regressions of observationsagainstpredictionsarecommonlyusedto makethe comparisons. Theclosertheslopeandcoefficientof determinationfor a regressionareto unity, and the interceptto zero, the betterthe validity of

a model.However,thereare theoreticalandpracticalproblemswith validationbasedon regressionanalysis,41 and the confidenceof the model builders should be recognisedas a model undergoesdevelopmentand modification.42,43 Of course, serious users also developconfidencein a model throughlessformal validationsas they compare predictionsagainsttheir own observationsandexperiences.In practice,validation is anongoingactivity thatwarrantsconsiderableeffort by themodelbuildersand independentexperts, particularly when the model attempts to mimic large variation in productionsystemsandis usedasan aid to politically or financially sensitivedecisions.44 In essencea modelis ‘valid’ whenit sufficiently mimicsthe real world to fulfil its objectives,and when decisionsbasedon the model are superiorto thosemadewithout the model.45 12.4 Simple model of herd structure It is obviousfrom Fig. 12.1andTable12.1thatfor agivenfarm, thenumberand classof cattle in the animal subsystem depends on the amountand quality of growthin theforagesubsystem. Theseinteractionsarecapturedin thefollowing simple empirical model of herd structure in relation to broad management options.It alsoillustrateshow a modelthat incorporatesa few basicparameters canbe a powerful analytical tool. Thenotionof farm carrying capacity(CC) is agoodstarting point.This is the long-term safe stocking rate for a farm, one that does not causeecological deterioration of theproduction system.It is a vital conceptfor managedgrazing systems that incorporate the biological, commercial and social elements pertaining to good land care.It is commonly usedto quantify a farm for sale or leasing in Australia andtheUSA, andbecausedifferent classesof cattlehave differentnutritional requirements,it is commonly expressed asadult equivalents (seeequation (12.1)). In rangelandswhere foragegrowthis dependenton rainfall, carryingcapacity is largely dependent on the amount of forage growth andon the proportionof growth that can be eaten(utilisation, U) without causing degradation of the pasture. Thus,basedon the reportby Johnstonet al.32 CCˆ R WUE A U=I …AE† …12:4† where CC is farm carrying capacity, R is effective rainfall (mm/year, in subtropical climates this is annual rainfall less runoff), WUE is water use Modelling beefcattle production to improvequality 251 efficiency(e.g.5kg/ha/mm), A is areaof thefarm (ha),U is safeutilisation (e.g. 0.25)andI is annualintakefor anadultanimal(e.g.4000kg/year).Whilst WUE varieswith theinherentfertility of thesoil, fertili serapplicationsandpresenceof trees,it is simple to measure. On the other handU is not simply measured but studies haveshown it ranges from about0.1 in arid infertile environments to about0.5 in moist fertile environments.Although equation (12.4)demonstrates the derivation of CC from first principles, in practice farm CC is usually determined from local knowledge and experience.32 The next task is to determine herd structureor the distribution of carrying capacity acrossthe various animalclasses. Whenall cattle on a farm originatefrom the breedingcows(i.e. no off-farm purchases)the systemis characterisedby threeperformanceindicators, which underpin a simplebut versatile mathematical model of herdstructure. (1) Weaning rates refer to the number of calves weanedper hundred cows mated.This key indicator dependson the nutritional health statusof cows andon the numberandfertilit y of bulls. It commonly rangesfrom 95% in high-performing herds to less than 50% in herdsof poor performance, a value that will not sustain the herd in the long term. (2) Survival ratesrefer to the proportion of eachclassof cattle that survivea year. Mortality from poor health, accident or predators is common, particularly in extensivelymanagedbeef production systems. The animal classesmost prone to mortality are breeding cows and calvessoonafter weaning. Clearly high survival ratesaredesirableandsusceptible classesof cattle commonly receive special feeding to avoid mortality from poor nutrition. (3) Culling ratesrefer to the proportion of breeding cows culled annually for age,infertili ty, or other imperfections.Hence,if the effectivebreedinglife of a beef cow is about ten years, culling helps to maintain high weaning rates.The rate of culling, plus the mortality of breeding cows definesthe numberof replacement heifers required to maintain a constant numberof breedingcows. The following model, which is suitablefor a spreadsheet, providesa ‘steady state’ estimateof number in thevariousclassesof cattlein aherd(herdstructure, Table 12.1), in responseto a few key assumptions and parameters, and local knowledgeof performancecriteria. The modeldepends on four assumptions.46 First, all animal classeson a farm with breeding and growing cattle can be specified by a manager, and are related numerically to the number of cows mated,providedextra animalsare not purchased.Second,the overall carrying capacity of a farm, in termsof number of adult equivalents, is eitherknown or canbe estimatedby equation (12.4).Third, for simplicity, cowsandcalvesare regardedasasingle animalclassuntil thecalvesareweaned.Fourth, thenumber of cowsmated(CM) is fixed for eachsituationbecauseif onediesor is culled from thebreedingherdit is replacedwith a heifer. Thus the ‘n’ classesof cattle on a farm canbe represented as 252 Meat processing CCˆ A1CM ‡ A2CM ‡ A3CM ‡ . . . AnCM …12:5† andafter collection of termsandsimplification

CM ˆ CC= X Ai …12:6†

whereAi is a coefficientthat relatesthenumber of animalsin the ‘ i’ th classof cattle to CM, the numbersof cows mated.Ai is the product of four factors: Ai ˆ PFi CFi SRi BRi …12:7† wherePFi is a flag to indicateif the ith classof animalis present(1, present;0, absent); CFi is a factor to convert the ith classof animal to adult equivalents (Table 12.1); SRi is the proportion of the original number surviving in the ith class;andBRi is theratio of thenumberof animals in the ith classto thenumber of breederswhensurvival in the classis 100%. WR is weaning rate, expressedas a percentageof the number of calves weanedto numberof cowsmated.If half theweaners areassumedto befemale, it follows that BRiˆWR/2 for eachclassof steersin the herd,and for heifer cattleBRi is similar to steersuntil replacementheifersenterthe breeding herd. Replacement heifersenterthe breedingherdwhen two or threeyears of age by adjustingPFi accordingly. First deadcowsarereplaced(DEATHSˆ percen- tage of CM dying eachyear), then culled cows are replacedaccording to a specifiedculling policy (CULLˆ preferredpercentage of CM replacedeach year).If therearetoo few heifersfor theculling policy, all availableheifersare usedasreplacements andtheshortfall is notedby the lack of surplusheifers for subsequentsaleand a reducedratio for culling. If thereare too few heifersto replacethe deadcowsthe herdcannotbe sustained.Thus for culled cows: BRcull cowsˆ MAX…0;MIN…CULL;WR=2ÿ DEATHS†=100† …12:8† andfor any surplusfemales BRsurplus femalesˆ MAX…0; …WR=2ÿ CULLÿ DEATHS†=100† …12:9† Oncethenumberof cowsmatedhavebeencalculatedusingequation(12.6), the number of cattle in the remaining animalclassesis given by Ni ˆ CM PFi SFi Bri …12:10† wherei > 1 sincefor cows,beingclass1, NiˆCM. Table 12.2 illustrates the application of this model to four scenarios pertaining to breedingandgrowing beefcattleon extensive rangelands.Case1 represents a herd where disease and/or poor nutrition severely restricts performanceof the breedingherd and this limitation is removed in Case2. Case3 is similar to Case2 exceptfor a 50%increasein farm carrying capacity, which might occurthroughfarm developmentoptionssuchasbuying moreland, controlling woody weedsor sowing improved pasture. Case4 illustrates the effectson herdstructureof a further improvement in performance of breeding cowsalong with a reductionin ageof selling steersandmatingheifers,asmight Modelling beefcattle production to improvequality 253 occur from a further improvementin herd nutrition and management.Whilst Table12.2is astaticrepresentationthatignoresthetransitionalstatesthatwould occurwhen changingfrom Case1 to Case4, it showsthebroadimplicationsof managementoptions on herd structureand number of cattle for sale. It also illustratesthatsimple ‘spreadsheet’ modelscanbea useful first stepin selecting broadmanagementoptions that warrant a moredetailed evaluation. 12.5 Future developments Modelling pastureandanimalproduction hascome a long way in threedecades. Its futureasanaid to researchis assuredsinceit providesdirectionandcontext to researchprograms. While farmershavebeenslow to adoptdecision supportpackagesthat aid routine decisions,professional advisorswho needto give good adviceto many clients are more receptiveto new tools that assistin evaluatingmanagement options within complex systemsacross a wide rangeof environments. Future developersof farm managementmodels will probably regard farm advisorsor service agenciesratherthanfarmersastheprimarycustomers.Also, themodels will be more user-friendly through the use of improved graphics and visualisation techniques, and the provision of support and upgrades via the World Wide Web. The scopeand rangeof policy modelsare expandingrapidly becausethey providepolicy makerswith an objectiveassessmentof complexproblems.This Table 12.2 Herd structuresgeneratedby the simplemodelgiven abovein responseto changesin keyparametersthatmightoccurashealth,nutritionandmanagementimproves in a ‘closed’ herdconsistingof breedingandgrowingcattleon extensiverangeland Key parameters Case1 Case2 Case3 Case4 Farmcarryingcapacity(CC) adult equivalents 1000 1000 1500 1500 Weaningratio (WR) (% of cowsmated) 50 80 80 90 Cow mortality rate (DEATHS) (%) 15 5 5 3 Ideal culling ratio for cows(CULL) (%) 20 20 20 20 Age of steersat sale:years 4 4 4 3 Age of surplusheifersat sale:years 3 3 3 2 Simulatedresults Total numberof cattle in herd 1088 1121 1682 1700 Numberof breedingcows 421 303 455 532 Proportionof herdasbreedingcows(%) 39 27 27 31 Numberof culled cows 42 61 91 106 Proportionof breedingcowsculled (%) 10 20 20 20 Numberof surplusheiferssold 0 44 66 112 Numberof steerssold 99 114 171 227 Total numberof cattlesold 141 219 328 446 Proportionof salecattle in herd(%) 13 20 20 26 254 Meat processing trend will continue,but policy modelsare likely to expandfrom the traditional biophysical base to include socioeconomic componentsand estimatesof the impact of policies on the ‘tri ple bottom line’ – ecological sustainabilit y, profitability andsocialacceptability.47–49 Indeed,a future challengewill be how to better integratethe technologiespertainingto hardand soft systems,suchas pastureandanimalproductionmodelsbeingpartof participatoryactionresearch, andtherebyinvolving stakeholdersin defining andevaluatingpolicies.16,50 A globalnetwork of information for model developmentandprovensoftware modules is expanding through the World Wide Web. Model developers will have increasing access to libraries of algorithms, and computer operating environmentswhich will encouragemorerapiddevelopmentof newmodels and a rich set of sharedapplications and experiences.However, since models are repositories for information and results from past research, there remains a global need for scientists and government agenciesto organise creditable databases of information, which are critical to the future development of decision support systems and integrated policy

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In People and Rangelands:Building theFuture, D EldridgeandD Freudenberger (Eds), Proceedings of the VI International Rangeland Congress, Townsville, Queensland,Australia, 19–23July, 1999,2, 850–1. 258 Meat processing 13.1 Introduction Throughout the European Union (EU) consumers are requiring the food industry to provide them with an increasing range of safe, nutritious and healthy chilled foods of high sensory quality and an increased shelf-life. To meet the demand for healthier food of high sensory quality, the use of additives and preservatives is being reduced or eliminated and minimal processing techniques introduced. To increase food safety whilst maintaining or increasing storage life, a considerable amount of time, effort and money has been spent in adopting HACCP techniques, including the use of mathematical modelling of microbial growth, better packaging methods and improved temperature control within the chill chain. Nevertheless there is little, if any, sign within official statistics of significant reductions in the incidence of food-borne illnesses within EU countries. Over the period 1982–94 cases have risen by 330, 50, and 200% in Spain, Norway and the United Kingdom respectively. In one year, 1988–89, cases rose by 28% in Belgium, 75% in France and between 20 and 26% in Germany. Poultry, red meat and meat products together make up the largest single source of food poisoning in the EU. For example, 47% of the outbreaks in Belgium, 38% in Sweden and 45% in the UK were attributed to poultry and red meat. Wastage due to microbiological spoilage and poor appearance due to desiccation is also high from meat and meat products. There is no terminal step (such as cooking) to eliminate pathogenic organisms from many raw products such as red and white meat until it reaches the consumer. The consumer is relied upon to adequately cook the meat sufficient to kill any bacteria injurious to health prior to ingestion. Several of the pathogens present on meat are psychrotrophic and can grow at refrigeration 13 New developments in decontaminating raw meat C. James, Food Refrigeration and Process

Engineering Research Centre (FRPERC), University of Bristol temperatures. Centralised processingand preparation of these products is growing, increasing the distance and time between initial preparation and the consumer, thusincreasingtherisk of growth of pathogens. Ideally,someform of terminal step should be introduced, failing that any step that reducesthe microbial load would be advantageous to public health and of economic significance to the industry. That is provided sucha step did not changethe intrinsic natureof the food, i.e., the ‘raw’ produceor meat must remain ‘raw’ . It would be expected that improvementsto slaughteringprocedures should result in a significant reduction in bacterial contamination of carcasses.It is therefore very disappointingthat the last published scientific survey(Hinton et al., 1998)reportedthat‘It can. . . besafelyconcludedthatthere is little evidence of anymajorchangein thebacteriological quality of British beefduringthe last 10–15years’.Therewould seemto beno basisfor believing that thesituation is different in the UK from that of other EU member states.The main effect of introducing newprocedures,however,appears to be a changein thedistribution of contamination ratherthan a substantial reductionin total number(Jameset al., 1999).In thefew caseswherea generallylower microbial contaminationhas beenreported, thereductionswerequitesmall. For example,comparisonsof two dressing methods in New Zealand reported changes ranging from a 1.41 decreaseto a 0.5 log10 ColonyFormingUnits cm ÿ2 increase in bacterialcounts at different positions(Bell et al., 1993).The application of ‘strictly hygienic’ proceduressuchassurgical gloves anddisinfectedknives undernearlaboratory conditions have been found to have a significant effect on levels of contamination. However, attemptsat transferring laboratory technology into commercialoperations havemet with limit ed success. Many studieshaveshownthat at the time of slaughterthe muscletissueof a healthy animal is essentially sterile (Gill, 1979). The surfaceof the meat is contaminatedwith pathogenic and spoilage organisms during slaughter and subsequent handling. Exposedsurfaces of the hide, fleece and skin of cattle, sheepandpigs, andthefeathersof poultry arecoveredwith dust,dirt andfaecal matter. Further contamination can occur from exposure to intestinal contents, which like faecescontain salmonellas and campylobacters – the two most commoncausesof food-borne disease. If microbeson thesurfaceof meat could be eliminating or substantially reduced immediately after slaughter the risk of cross-contamination during processing would be substantially reduced.An efficient method of surface decontamination therefore offers substantial advantagesin termsof food safety,spoilageandeconomics. 13.2 Current decontamination techniquesand their limit ations Many decontamination techniques have beensuggested and studiedover the years. However, manyof these haveonly beenattemptedon a laboratoryscale. Methodsof decontaminating meat can be divided into thosethat rely on the 260 Meat processing activity of physicaltreatmentsandothersthatusechemicals to eitherremoveor destroythe microorganisms. 13.2.1 The problems of decontaminating raw meat Animal carcassesare not ideal shapesto decontaminate.Most decontamination treatmentsrely on physicalcontactand uniform coverageof the meatsurface. This is difficult, asthesurfacesof manyproduceandwholeanimalcarcassesare very irregular.For example,theoutersurfaceof a carcasshasmany crevicesand folds. Theseareasare very difficult to treat and provide protectionto attached bacteria.They slow down the penetrationof aqueousand gas treatmentsand causeshadowingproblemsfor radiationtreatmentssuchasultraviolet (UV) light. As well asprotectingbacteria,theseareasoften clog up with physicalcontami- nation,suchasdirt andhair, anddo not drain well. Pools of wateror chemical solutionslying in theseareascanhavea detrimentalaffectson thevisualquality of the meatandcausedifficulties in controlling the contacttime of treatments. Thereis much evidencethat the time at which products are treatedgreatly affectstheefficacy of decontaminationprocesses. The longerbacteriaresideon product surfaces,the moredifficult removalbecomes, becauseof the ability of bacteriato attach to tissue.Bacteriadiffer in their ability to attach to different surfaces and the time they requireto becomefully attached.The formation of bio-films may increase the resistance of bacteria to disinfectants such as chlorine. Surfactants such as ‘Tween 80’ have beenused to increase surface wetting,in theory allowing thedisinfectantto ‘get at’ thebacteria. ‘Tween80’ is not used for food production because it causes unacceptable organoleptic changes. Two surfactants, ‘Orenco Peel40’ and ‘Tergitol’, are usedfor fruits andvegetablesin the USA (ZhangandFarber, 1996). 13.2.2 The difference betweendecontamination methodsand treatments Thereis rarely any distinction made in the literaturebetween decontamination ‘methods’ (i.e., the method of applying a treatment) and decontamination ‘treatments’.This oftencloudsthepractical issuesof decontamination.Thereis often too much emphasisplacedon the treatment rather than the methodof application. Decontamination is not a matter of simply dipping or sprayingthe product with chemicals or water,or giving it a quick flashof light. For example, manyfactorsaffect theefficiency of aqueous spraysystems.In automatedspray cabinets thepositionandnumber of thesprays, theshapeof thespray,andspray pressures,all havea significant effecton thetreatmentirrespective of thenature of the substancebeing pumped throughthe sprays.Many studies haveshown that the methodof decontamination is often moreimportantthanthe treatment. Most abattoirshave relied in the paston manualsprays to washred meat carcasses; thus, automatedspray cabinets have been a natural development. Somestudies,however, haveshownthat a delugemethodof application where the carcassis passedunder a waterfall offers a more effective method of New developmentsin decontaminating raw meat 261 coverage(DaveyandSmith,1989).Theuseof watersprays is currently themost common methodof cleaningcarcasses.Many studieshavebeencarried out to optimise sprayingsystems and investigate their efficiency. Extensive related studieshavebeencarriedout in theUK by Bailey (1971),in Irelandby Kelly et al., (1981), in the USA by Anderson and coworkers on the CAPER system (Andersonet al., 1984), and in Australia by Smith and Davey (1990). In a number of these studies the effect of addingorganicacidsand chlorine to the water systems was evaluated. Together these studies provide essential informationon the parametersthat affect spray washing. Physicalparameters include spray pressure and flow rate, and nozzle type, configuration and the angle of spray.As well as thesephysical parameters variablessuchas tissue type, inoculation menstruum, inoculation amount, or temperatureof treatment all affect the resultof decontamination procedures. Heat treatments,with or without chemicals,arevery relianton themethodof application. To preventcooking the product,suchtreatmentshaveto providea uniform heating of all surfaces for a short period. This is not particularly difficult to achieve on a laboratory scale,sprayingor dipping small samples using hot water for example. Similarly, laboratory studiesusing steamhave shown that if very high temperaturesareappliedfor very shorttimes,followed by coolingthesurfacerapidly, highbacterial reductionscanbeachievedonmeat without affecting the surfaceappearance.However,successfully applyingsuch techniquesto carcasses in an abattoir,for instance,presentsmanyengineering challenges. 13.3 Washing Washing meat or produce with water can effectively remove physical contaminatessuchassoil, hairsandotherdebris,howeverits affecton bacterial numbersis marginal.Thetemperatureat thesurfaceandthemethodof applying the water are the two most important factors in bacterial removal.While it is generally accepted that washing is an effective method of removing visible contamination from meat carcasses, there is persistentcriticism that it may redistributebacteriaover thecarcass.At present,mostwashesutili secold water andtheevidenceis thatcold waterhaslitt le effecton microbial numbers.Trials on sheephaveshownthat washing led to bacterialcontamination of the dorsal area, which was uncontaminatedbefore washing (Ellerbroek et al., 1999). Contamination on the ventral areawas not reduced, an areamost likely to be contaminated during dressing operations.Residual water remaining on the carcasswas believed to enhancebacterial multiplication during storage. Cold waterwashing of beefcarcasseshasbeenshownby onestudyto be ineffective and tending to bring abouta ‘posterior to anterior redistribution’ (Bell, 1997). However, another study (Charlebois et al., 1991) found that there was li ttle differencein the distribution of faecalcoliforms beforeandafter trimming and washing on beef carcassesin threeabattoirs. 262 Meat processing Washingwith wateralone usuallyobtainsa reductionin microbial numbers of 1- to 2-log-units (10 to 102) on meat.Increasingthe temperatureof thewater increasesthe reduction.However, a sprayjet rapidly loses heatby evaporation. Studieshaveshownthat the maximumimpact temperatureon the carcassof a sprayplaced30cm awayandsupplied with waterat 90ºCis approximately 63ºC (Bailey, 1971). Abattoirshavealwaysbeenworriedabouttheeffectof hot water on theappearance of carcasses.However, studies(Smith,1992)haveshown that treatmentsof 80ºC for 10 s not only significantly reduce bacteriallevelsbut do so without any permanent damageto the surfacetissue. Automatedwashing systems for meatcarcasseshavelong beenseento bethe way forward.Themostcomprehensivepublicly documentedstudiesto datehave beenontheCAPER (CarcassAcquiredPathogenEliminationReduction) system developedin the USA and the Australian ‘Deluge’ system. The Australian systemdepends on the action of hot water solely to decontaminate.While the CAPER system has beendesigned as a two-stage process involving a water stageto removephysicalcontaminationandorganic acidsto sanitisethecarcass. Commercial spraycabinetssimilar to the CAPER system are available in the USA, while trials havebeencarriedout on a commercialversion of the deluge systemin Australia. 13.4 The useof chemicals Many studieshavebeencarriedout to testgroupsof chemicalsfor antimicrobial activity againstspecificpathogenicandfood spoilageorganisms.A wide range of chemicals are known which will destroy or severelylimit the growth of pathogenic and spoilage bacteria. However, the numberof chemicals that are likely to be approvedfor useon meatis severely limited (Table13.1), not least because of legal restrictions. While chlorine has been an accepted part of washing fruits andvegetablesfor manyyears,chemicalwashing of redmeathas not generally beenaccepted. The poultry industry hasutilised chlorine to keep chiller waterclean,which hashada knock-onaffecton microbialcounts,but its use in the EU is being stoppedfollowing health concerns. More recently trisodium phosphate (TSP) has beenusedfor poultry. There is also growing interest in the use of ozone and naturally occurring antimicrobials. The effectivenessof most chemical treatmentsdepends on concentration,application temperature andexposuretime. 13.4.1 Appl ication of chemicals Whenconsideringall chemicaltreatmentsthemethodof applicationmustalsobe considered.In many cases,theseare ‘drop-in’ additionsto the washingprocess ratherthanan

integralpart of the washingsystem.Most chemicalsareappliedin the form of aqueoussolutionsthereforeas with water treatmentsthe methodof applicationwill havea significantinfluenceon how effectivea treatmentwill be. New developmentsin decontaminating raw meat 263 Most of thechemicalsdescribedhavebeeninvestigatedin laboratorystudies by dippingsmallsamplesof meatinto solutionsof thechemicals. Immersion is a very effectivemethodof ensuring full coverageof a product. However, thereare a number of practical problems with immersion. Aside from the logistical problem of immersing a side or whole carcass, maintaining chemical concentration is diffi cult. As well asbeing lost throughspillageandabsorption by the meat,the activity of the solutionwill changeasthe chemicalreactswith the microorganismsandother organicmaterial. Acid solutions lose activity as the anions are easily bound by peptides and proteins releasedby the meat. Chlorine also reacts with organic material. Ozone and hydrogen peroxide in solution rapidly decompose.While immersion maybepracticalfor cutsof meat, (sub)primalsandpoultry carcassesit is unlikely to beadopted for treatingsides andcarcasses. Spraying is the most common way of applying chemicals to carcasses.Most studies haveusedmanual spray devices.The effectivenessof a manualsystem, whether it is using just water or a chemical spray, depends very much on the skill of theoperatorandwill vary from operatorto operator.Thismeansthatany results are difficul t to quantify. Even the effectivenessof automatedcabinet systems depends upon the influence of various physical parameters.These parametershave been coveredin the earlier section on spraying with water. Mostof thecabinetstudieshaveusedequipmentbasedon theCAPERsystemor onemadeby USCHAD Co.,thoughanumberof groupshaveusedpurpose-built systems. Table 13.1 Chemicalsinvestigated,with varying success,to decontaminatemeat Organicacids Lactic, acetic,fumaric, citric, ascorbic,formic, propionic, benzoic,sorbic Chlorine Gaseouschlorine,sodiumhypochlorite,calciumhypochlorite Chlorinedioxide Sorbates Potassiumsorbate,sorbicacid Polyphosphates (Trisodiumorthophosphate(TSP),sodium hexametaphosphate,sodiumtripolyphosphate,tetrasodium pyrophosphate) Ozone Hydrogenperoxide Potassiumchloride Lysozyme Disinfectants (Glutaraldehyde(1,5-pentanedial),Poly hexamethylenebiguanidehydrochloride(PHMB), Iodophor, Cetylpyridiniumchloride (1-hexadecylpyridiniumchloride) (CPC),Carntrol(activeingredientcoppersulfatepentahydrate), Timsen(40%N-alkyldimethylbenzylammoniumchloride in 60% stabilisedurea)) 264 Meat processing 13.4.2 Chlorine Thevariousformsof chlorineareprobably themostwidely usedsanitisers in the food industry. They include gaseous chlorine (Cl2), sodium hypochlorite (NaOCl), calcium hypochlorite (Ca(OCl)2), andchlorine dioxide (ClO2). Apart from ClO2, which has a different mode of action, these compoundsform hypochlorousacid (HOCl) in aqueous solution, andit is this form that is active againstmicroorganisms. The anti-microbial action of all chlorine compounds is dueto their oxidising affect.However, while chlorine is widely usedin the EU by the food industry to washvegetables,particularly saladvegetables,it is not permittedto beusedon meat. Despite this, scientific trials havebeencarriedout on its applicability. Many studies have shown that applying chlorine at concentrationsof 200 ppm and aboveto meatcarcasses can produce a 2 log (10)2 reduction in bacterial numbers.Thesereductionscanbe further increased by raising the temperature of the chlorine. Most pathogenscan be readily controll ed, though not eliminated, by chlorine but some would require concentrations higher than 200ppm. It is very unlikely that chlorine concentrationsabovethis level would be allowed legally for meat. Numerous concernsare increasingly being expressed about the use of gaseouschlorine andhypochlorite solutions.Amongthese arethe fact that they react with phenolic compoundsand the resultant chlorophenols can cause tainting at very low concentrations, as well as possible human health risks associated with chlorinated lipids and proteins. Chlorine dioxide has been proposedasa safealternativesince it doesnot reactin this way. Therearealso many practical problems in terms of control of chlorine levels, protection of delivery systems from corrosion, etc. 13.4.3 Organic acids Thereare many commerciallyavailableorganicacids. The effectsof different concentrations,temperaturesandmixturesof many of these havebeenstudiedon meatmicro-flora.Acetic andlactic acidhavebeenthemostwidely studiedof the organic acids, while propionic, citric and fumaric acids have also been investigated.Organicacidsarenaturallypresentin manyfoods,andarerelatively cheapastheyaretheprincipal productsof manynaturalfermentationreactions. Theeffectof organicacidsdepends on threefactors (Ingramet al., 1956);(i) the effect of pH, (ii) the extentof dissociation of the acid, and (iii) a specific effectrelatedto theacid molecule. In generaltheantimicrobial actionof organic acidsis dueto pH drop.The lower the pH the greater the effect. Lowering the pH, however, through theaddition of an inorganicacid is ineffective (Reynolds and Carpenter,1974). Dissociation of the acid is also a factor. Undissociated weak acids are 10 to 600 times as effective in inhibiting and kill ing microorganismsasdissociatedforms (Eklund,1983).Organic acidsaremainly undissociated when dissolved in water. They therefore have a stronger antimicrobial action than inorganicacids that are totally dissociated in water. Buffering the acids(throughthe additionof a solublesalt of the baseacid) will New developmentsin decontaminating raw meat 265 increase their effectiveness, as more undissociatedmolecules will be present. Evenunderthesameconditionsof pH andaciddissociationtherearedifferences in the antimicrobial actionof variousorganic acids (deKoos,1992),this is due to the natureof the anion (Smulders,1995). Washesandsprayscontaining organicacidshavebeensuccessfullyusedin decontaminating beef,lamb,pork andpoultry carcasses.Researchers agreethat organic acidscanreduce the numbersof pathogenicandspoilage organismson meat by typically 1 to 3.5 log microorganismsper g producing an extension of shelf life of 7 to 17 daysrespectively. In investigationswhere thetemperatureof theacid is varied,greaterreductionsin bacterial numbersareachievedat higher temperatures.However,in manycases the meat hasbeenimmersed in the acid mixture andit is difficult to separate the effect of the temperaturefrom that of the acid. Studieshavegenerally usedconcentrationsof between2 to 4% with someas high as24% andit is not clearwhat shouldbe the maximumconcentration.In some studies concentrations of 2% acetic acid were reported to produce discolouration on pork loins (Cacciarelli et al., 1983). In others, at 3% no adverse effects were found on lean samples but slight off flavours and grey discolourationwasreportedon fats (Andersonet al., 1979a).Overall, treatment with 2% lactic acidsolutionsapplied at a meatsurfacetemperatureof 37ºChave beendescribed as optimal (Anderson and Marshall, 1989). Someresearchers advocate a mixture, others singleacids. It is disappointingthat thereductionsproducedin commercial trials areoften significantly lower thanthose foundin laboratorystudies.In laboratorytrials the samples haveoften beeninoculated with high levels of bacteriaand in these situations the acids may be more effective. Also, producing an even surface coverageof acid is far easieron a small samplein the laboratorythan over a whole carcassin the abattoir. 13.4.4 Polyphosphates Trisodium phosphate (TSP) was developed in the US for the control of salmonellaonpoultry. TSP(Na3PO4) possibly worksby removinga thin layer of fat from the carcasssurfaceand in doing so removing the microorganisms attachedto the surface(Giese,1992),it thencauses ruptureof the bacterialcell membrane.Rupturedcells arenot protectedandsuccumb to the ionic strength andhigh pH of the medium. Thereareconflicting reportson thesensitivities of Gram-positive andGram- negative bacteria to polyphosphates. It has beenreported that Grampositive bacteriaaregenerally moresensitive to polyphosphatesthanareGram-negative bacteria (Leeet al., 1994),but TSPhasbeenreportedto bemore activeagainst Gram-negative bacteria, such as Salmonella spp., Campylobacter spp. and Pseudomonasspp.(Corry andMead, 1996).Thereareconflicting reportson its effectivenesson reducingmicroorganismson red meat tissues(Dickson et al., 1994;Gormanet al., 1995). 266 Meat processing 13.4.5 Ozone Ozone (O3) is a water-soluble naturally occurring gas that is a powerful oxidising agent. It is alsovery unstable, on exposure to air andwater it rapidly decomposesto form oxygen,hencegeneration is usuallyat the point of use.In general, bacteria are more susceptible than yeasts or moulds; Gram-positive bacteria are more sensitive than Gramnegative; bacterial sporesare more resistantthan vegetative cells. Temperature, relative humidity, pH, stageof microbial growth andorganicmatterpresenthaveall beenshownto affectozone antimicrobial action. Gaseousozonewasusedcommercially in the1940sto extendtherefrigerated storage life of meat (Ewell, 1943). The use of gaseous ozone in meat- conditioning coolershaslong beenacceptedby the FDA in the USA (Graham, 1997). However, meat pigments and fats are sensitive to oxidation by high concentrationsof ozone( 10ppm).Studiesusing ozonatedwaterhavereported conflicting results,somereporting advantages over other chemical treatments, othersshowing no advantages over washing with water alone (Reagan et al., 1996). 13.5 New methods: steam Steamat 100ºChasa substantially higher heatcapacity thanthesameamount of water at that temperature.If steamis allowed to condenseonto the surfaceof meatit will rapidly raisethesurfacetemperatureof themeat.Oneveryattractive feature of condensing steamis its ability to penetrate cavities andcondenseon any cold surface.The basis for why steamtreatment neednot cook raw meat while killing bacteriaandthepenetrativeability of gaseshasbeendealt with by Morgan et al. (1996a). Heat kills bacteriamainly by inactivating the most sensitive vital enzymes.Typically theheatof activation of theseenzymesis 8.38 to 50.28kJ(g.mol)ÿ1. The heatof activation for irreversible musclecooking is 209.5 to 419 kJ(g.mol)ÿ1, substantially higher. Only microgramsof enzyme need to be inactivated compared to the grams of muscle denatured during cooking. ‘For a square centimetre of surfacecontaminatedwith 100bacteria,15 milli on times asmuch heatis needed to cookthesurfaceto a depth equalto the length of a bacterium compared to the heat needed to kill all the bacteria’ (Morganetal., 1996a).Sincebacteriaarepresentonly on thesurfaceof themeat evenassuming that heatingratesare the sametheoretically the bacteria should die earlier thanthe meat would cook. In fact the meatwill take longersinceit requires conductive heat transfer through the muscle. Exposure times for chickenmeat in air-free thermally saturatedsteam at varioustemperaturesare shownin Figure13.1,an equivalent time in 100ºCwaterwould be about1000 ms. Water vapourmolecules are much smaller than bacteria,for example 2 by 10ÿ4m in diameter comparedwith 0.7 by 4m for Salmonella cells (Morgan et al., 1996a). Therefore steam is capable of reaching any bacteriain cavities. New developmentsin decontaminating raw meat 267

Although the velocity of steamis reduced by cavitiesof diameter lessthanthe mean free pathof the gasdensitythis doesnot restrictsteam reaching bacteria. In 140ºC saturatedsteam,the meanfree pathof the steammolecule is 0.4m, half thediameterof thesmallest cavity capableof containinga Salmonella cell. To preventcookingthe steammustcondenseon the surfacerapidly, andre- evaporateequallyrapidly. Gasesmoveby eitherflow or diffusion.Flow is rapid, motivatedby a pressuregradient. Diffusion is much slowerandmotivatedby a concentration gradientof the gasthroughother gases.During steam treatment air, andanyother non-condensable gaspresent, is concentratedby the inrushof condensing steamforming a layer around the product surface. This prevents steamflow, slowing condensationasthesteamdiffuses throughthe layer.Noncondensable gasescan come from threesources; gasesaroundthe meatwhen enclosedin the chamber; gasesenteringwith the treatment steam; and gases which have been desorbed by heat from the meat or other surfaces. The temperature at which water boils is a function of pressure. At atmospheric pressure, steam will initial ly be created at 100ºC. At lower pressures the generation temperaturewill be lower, at higherpressuresit will be higher. Two laboratorystudieson thedirectapplicationof steamthrougha hoseto a meat carcassreport conflicting results.In one study, direct treatment of pork carcassesshoweda reduction of total bacterialcountsof 6 log micro-organisms per cm2 (Biemuller et al., 1973).However, the steammarred the appearance of Fig. 13.1 Time for cookingto beginon broiler meatpiecesexposedto steamat various temperatures(adaptedfrom Morganet al., 1996a). 268 Meat processing thecarcasses.In contrast a study on beefcarcassesshoweddirectapplicationto be ineffective andto reduce storagelife (Andersonet al., 1979b). The effects of various steamtreatmentson the appearance, shelf-life and microbiological quality of chicken portions have been investigated at the University of Bristol (Jameset al., 2000a). Application of steamat atmospheric pressure(100ºC for 10s) on naturally contaminated chicken breastportions resulted in a 1.65 log10cfucm ÿ2 reduction in the numbers of total viable bacteria.However, in comparisonwith untreatedcontrols, this treatmentdid not extend the shelf-life. Steam treatment for up to 10s on chicken portions inoculatedwith analidixic acidresistantstrainof Escherichia coli serotypeO 80 resulted in a maximum reduction of 1.90 log10cfucm ÿ2. Overall, results indicated that significant reductions in microbiological numbers could be achievedon chicken meatusingsteam.However,the reductionsachievedwere lessthanwould be expected from the time temperaturecyclesachieved. Additional work at theUniversityof Bristol hascomparedsteamcondensation (100ºC for 8s), hot water immersionalone (90ºC for 8s), and chlorinatedhot water(250ppm,90ºCfor 8s) for treatinglambcarcasses(Jamesetal., 2000b).All threetreatmentsproducedcarcasseswith loweraerobicplatecountsthanuntreated controls(averagecountof 3.2log10cfucm ÿ2). Therewasnosignificantdifference betweenthesteamandhot watertreatmentswith both treatmentsreducingcounts by approximately1 log10cfucm ÿ2. Overall the chlorinatedhot water treatment reduced counts by 1.6 log10cfucm ÿ2. Although chlorine proved the most effective, the authorsfelt that current attitudestowards the use of chemicals relegatedits usein comparisonwith the other two treatments. Steamcan be produced undervacuumat temperaturessubstantially below 100ºCwithout substantially reducingits heatcapacity. Sub-atmospheric steam hasbeenshownto be an effective way of decontaminatingpoultry drumsticks and carcasses, surface temperatures of 75ºC for four minutes achieving reductions of the orderof 5.5 and3 log, respectively (Klose et al., 1971). EU andUK government fundedstudies, involving the University of Bristol, have been carried out on the use of sub-atmospheric steam pasteurisation systems for treatinga rangeof food products (Evans, 1999). During trials each food type wasinoculated with a pathogenanda spoilageorganism (Salmonella enteritidis andPseudomonas fluorescenson poultry, Escherichia coli O157:H7 and Pseudomonasfragi on beef and Yersinia enterocolitica and Pseudomonas fragi on pork). The sampleswere treated in a decontamination apparatus (developedaspartof thework,) at temperaturesbetween 55 and85ºCfor times between ten seconds and ten minutes and the reduction in microbial contaminantsdetermined.As anadditional treatment,organic acidswereadded before heat treatment and their effect quantified. The effects of three acids appliedat 10 or 55ºCwere investigated(acetic(0.15,0.23or 0.3M), lactic (0.1, 0.15or 0.2M), bufferedlactate anda mixture of aceticandlactic acids).Water appliedat 55ºCwasusedasa control. In theabsenceof acid or watersprays,steamat75or 85ºCfor 40secondswas required in orderto reducelevels of S.enteritidison chickenby 3–4 log cycles. New developmentsin decontaminating raw meat 269 Treatmentsof 75ºCfor tensecondsreducedY.enterocolitica onporkskinandE. coli O157:H7 on beefby 2–3log cycles.The addition of organic acidsincreased microbial reductions in all of the threemeatsinvestigated.The application of acids at high temperature (55ºC)andstrongermolarities wasfound to be most effective.Improvedeffectsof theacidswerealsofoundwhen thetimeof contact between the acid andthe food prior to steamtreatmentwasincreased.Contact timesof between four andsix minuteswererequired to achievereductionsin the pathogensstudied by 4 log10 cfu cm ÿ2 on pork skin andbetween5–6 log10 cfu cmÿ2 on beefor chickenskin. On all meatsacetic,lactic or a mixture of these acids were most effective, although when water was applied as control, reductions abovethoseachievedby steamalonewererecorded. This indicated that someof the actionof the acidswasto wash microbesfrom surfaces. Whensteamalone wasusedto decontaminatebeefsamplesthe shelf-life of samplesstoredat 0 or 10ºCin eithervacuumpacksor air wasextendedonly if the storagetemperature was maintained at 0ºC. When acids were applied in addition to steam treatment the storagelife of pork skin and chicken was extended.On thepork skin four acidswerecompared (0.3M acetic, 0.2M lactic, an acetic/lactic mixture andbufferedlactic). Of these acids,bufferedlactic was capable of retaining microbial counts below the pre-decontamination level for 14 daysif storedat 0ºCandfive daysif storedat 10ºC.Extensionsin thestorage life of decontaminatedchickensampleswhentreatedwith organicacids(lactic) andsteamwerealsofound.On theinoculatedandtreatedsamplesof poultry the levels of TVCs andpseudomonadsremainedbelow 6 log for 2–3 times longer than the control samples (for three days at 10ºC and 12 days at 0ºC). Total numbersof microbeson the treatedsamplesrequiredlongerperiodsof time to reach a set level. This was primarily because they had lower initial levels of contamination. The rate of growth of salmonellasurviving the heat treatment overthe20-daystorageperiodat0ºCwasnegligibleaswouldbeexpectedat this temperature.At 10ºCgrowth wasslow, but the overall increase did not exceed one log cycle during the five-day storage. This studyhasshown that re-contamination, after decontamination, of pork with Y. enterocolitica did not present a higher risk of increasedgrowth during aerobic storage(at 0 or 10ºC) on decontaminatedthanon untreatedpork when thenumbersof backgroundflora werelow comparedto the inoculatedbacteria. The risk was slightly greater when the samples were vacuumpackaged. On chicken, Salm.enteritidis grew well in aerobic conditions at 10ºC both on the decontaminatedandthe untreated meat. As E. coli O157:H7 hasa very low infectious doseand causesvery severe diseasethe consequencesof growth could be especially serious. In this study a storagetemperatureof 10ºCwasusedasa ‘worst case’.Whena high inoculum (3.6 log10cfucm ÿ2) was used,the multiplication was much more rapid on the decontaminatedbeef when vacuumpackaged. This was also the casefor the threeexperimentswith low inoculum, but therewasa greater variability in the results. Theseobservationsneedto beinvestigatedfurther,particularly asE. coli O157:H7 is known to beresistantto acids.However, it shouldbebornein mind 270 Meat processing that post-processrecontamination is likely to include mainly non-pathogenic (competitive) microorganisms, at least some of which are likely to compete successfully with E. coli O157:H7. In addition, raw meatshould be storedat temperaturessignificantly below 7ºC, which is the minimum temperature for growth of this pathogen. In all cases somedegreeof cookingwasapparent on the meatsinvestigated. On thechickenandbeeftheouter layer of musclewasslightly cooked, although theskin of thechickenwasbarelyaffected.With pork skin thesteamtreatment slightly influencedthe surfacecolour but did not affect consumeracceptability of thesamples.Whenacidswereaddedto thepork skin consumers wereableto detect an acid odour immediately after treatment,although the acid odour decreased during storage. Morgan et al. (1996a, b) have developeda device that enablesvery high temperature surfacetreatment of meat without cooking. This systemutilises very rapid cycling (for mill iseconds) of heatingandcooling usingsteamunder pressureand vacuumcooling. Meat samples are placedin a rotating chamber thatasit rotates is exposed to threeotherchambers, a vacuum, steam,andfinal vacuum.This allows temperaturesof up to 145ºC. Tests,using inocula of L. innocua on chicken meat, have shown that substantial reductions can be achieved. Subsequentwork showedthattreatmentat145ºCfor 25msproduceda 4 log reduction on raw chickenmeat. Treatment at 121ºCfor 48msproduced a 2.5 and1.9 log reductionon beefandpork samples,respectively. Themostsuccessfulsteamprocessyet, in termsof industrial application, has been that developed in the USA by Frigoscandia, the SteamPasteurisation System(SPS).Studieson this commercially available systemfor treating red meatcarcasseshavebeenconducted andpublished by KansasStateUniversity (Nutsch et al., 1995; 1996, 1997, 1998; Phebuset al., 1996a, b, c, 1997a,b, 1999;). Significant reductionsof the orderof 3.5 log-units for specificbacteria havebeenreported.The full commercial system(SPS400Steam Pasteurisation system) consistsof a threestagecabinet.Washedcarcassespassthroughanair- dryingstageto removeresidual waterfrom thecarcassbeforeanenclosedsteam treatment stagefollowedby spraycooling.Thefull unit is very large,‘the sizeof a subway car’ (Smith, 1996), and a single-steam unit (SPS 30 Steam Pasteurisationsystem) for small abattoirs hasalsobeenmarketed.Approval of the use of steampasteurisation as an antimicrobial step in the beef slaughter processwasgrantedby the USDA in 1995. Commercial evaluations of the SPShavebeencarried out in theUK undera MAFF LINK scheme,usinga SPSSC100 cabinet(Eveleigh,2000).Initial trials showed that both natural TVC and Enterobacteriaceae counts on carcasses produced in the abattoir involved in the study were too low to show any significant differences in process treatments before and after the SPS.Thus bacteriaweresurfaceinoculatedprior to treatment.TheTVC resultsshowedthat 85ºC had little effect, evenfor 12s, comparedto 90ºC, while there was little differenceat higher temperatures.This was taken to indicatethat therewerea number

of thermotolerant organismspresent.While results showedthat a 90ºC New developmentsin decontaminating raw meat 271 treatment for 8s would satisfyrequirementsfor an effective treatment with the least effect on carcasscolour, the participantschoseto carry out further trials using 90ºC for 10s, eventhoughtherewasa noticeable colour change. 13.6 Other new methods A whole rangeof more novel techniques,suchasmicrowaves(Patersonet al., 1995)ultra-violet light (Stermeret al., 1987)or visible light (MertensandKnorr 1992),havebeensuggested for treatingmeats, andin some casesdemonstrated to be viable alternatives. Most of thesemethodsdependon heatto destroythe bacteriapresentthough a numberof nonthermaltreatmentshavebeenproposed (Mertins andKnorr, 1992). Many of the alternative physical decontamination treatmentsrely on the effectof radiantenergy on surfacebacteria(Table13.2).Thesemethodsinclude ultraviolet radiation (UV), visible light, and lasers. Othersrely on the effect of electromagnetic fields andincludemicrowave,electricalstimulation (ES),high voltagepulsedelectric field (PEF)andoscillatingmagneticfield pulses(OMF). In additionhigh pressures, air ions andultrasoundhavebeeninvestigated. UV hasbeenusedto extend the storagelife of chilled meat.Many reports showthat exposure to UV canreducesurfacecontamination of meat by 2 to 3 log10CFUcm ÿ2 and it would appear to have no deleterious effects on the appearanceof the meat. Under high intensity UV, exposure times would be 1 log reductionin bacterial numbers.Few data,however, are currently availableon the process.Attaining very high surfacestemperaturesfor a very shortperiod using lasersmight also havemuchto offer in the future. The number of papers on the use of microwave energy for meat decontamination look promising. Papersreport that a 40 secondexposure can Table 13.2 Mode of antimicrobial action of different novel decontaminationtreat- ments Method Mode of actionon microbial cells Microwave Thermaleffect Ultraviolet light UV effect Pulsedlight UV (or thermal)effect Ultrasound Ruptureof cell membrane Ultra high pressure Denaturingof protein Pulsedelectric fields Ruptureof cell membrane 272 Meat processing reducebacterial countson chicken piecesby 2 log (Cunningham, 1978,1980). However, recentwork at the University of Bristol (Göksoy et al., 1999,2000) refute these claims. This work using domestic microwave ovens showed microwave heatingto be too unevenand unreproducable to surfaceheatmeat cutswithout cooking.Al thoughtherehavebeennumerouspublicationsclaiming a possible non-thermal antimicrobial affect of microwave exposure most reviewers of the literature have concluded that any destruction of micro- organismsin a microwave is purely thermal. Electrical stimulationappears to produce a small reduction in bacterial levels in laboratorystudiesonmodel foods. Reductionsof up to 6 log10CFUcm ÿ2 have beenreportedafter theapplicationof high voltagePEF(Zhanget al., 1994).The technique, however, is in its early stages and will require considerable development before it can be applied to small pieces of meat. Similarly the application of OMF appears to be an effective meansof destroyingbacteria, especially for treating liquid foods,but is not likely to haveapplicationsin the decontamination of meatin the nearfuture (MertensandKnorr, 1992). Ultrasound is effective only in a liquid medium and therefore has limit ed application for redmeatcarcassesthoughit mayproveuseful for treatingcutsof meat. Laboratory trials have shown that very high pressure processing is an effective methodof extendingthe chilled storagelife of highly contaminated minced meat (Carlez et al., 1994). It also significantly reduces the risk of survival of pathogenic microorganisms.The cost of high-pressureequipment that could processsubstantial quantities of meat, however,appears to limit its commercial uptake. 13.7 Future trends Meat carcassestypically contain between 101 and 104 microorganismsper g (James et al., 1999). To achieve any significant improvement in the microbiological condition of suchproducts we require a 4 log-unit reduction in total bacterialnumbers. To dateno adequate methodof achieving this has beenfoundwithout affectingthesensorial quality of meat.No treatment,asyet, can be relied upon to eliminate all pathogens.Typical reductionsfor non- chemical andchemicaldecontaminationtreatmentsareshownin Table 13.3and Table13.4, respectively. With the increase in commercial interest and use of decontamination treatments(particularly in theUSA) moreandmorestudiesarebeing carried out in operational abattoirsunlike much of the earlier work that was often on a bench scale. In the US commercial abattoirs are utili sing a wide range of decontamination treatments, often sequentially. While steamis beingapplied commercially in America,andundergoingtrials in the UK, for beefcarcasses,experimentalwork is still ongoingon its usefor othermeats. Much work at FRPERChasconcentratedon poultry while others have even applied it to delicatemeatssuch as fish. Despite the success and New developmentsin decontaminating raw meat 273 commercialrealisationof steampasteurisationsystemstherearestill holes in the understanding of thesesystems.To realisethe full potential of steamsurface pasteurisation it is necessaryto understandthe relationship between heating/ cooling cycles and appearance/quality changes for foods of interest. The conditions that will maximise bacterial reduction without significant quality changes need to be identified along with the engineeringunderstandingto produce those required conditions consistently over the surfaceof food when presented at industrial throughputs. While there are effective commercial systemsavailablethereis much evidencethat thesesystems still requirefurther developmentto achievefull efficiency. Many studiesstill concentrateon theefficacyof differentchemicals,oftenas combined chemical solutions. In the EU legal restrictions on the use of chemicals for treatingraw meat remain. Thus it is still unlikely that chemicals will find widespread application in the meat industry. However, chemical washing of fruits and vegetables is widespread and a growing research topic. Internationally, theleastcontroversial methodsof treatingmeatinvolve washing or someform of heattreatment. The adoptionof surfacedecontaminationtreatmentsby the meatindustry in the EU remains restricted by legislation on what should or should not be permitted. Meanwhile theadoptionof anE. coli ‘zero tolerance’ requirementin the USA, has effectively forced the American meat industry to use anti- microbial systems.Thus the introductionof efficient anti-microbial systemsin Table 13.3 Typical microbial reductionsachievedby non-chemicalmeatdecontaminationtreatments Treatment Log reduction(APCs) Water– cold 1–2 Water– hot 1–3 Steam 2–4 (6) Ultraviolet 0–2 Visible light 1–3 Microwave 1–2 Ultrasound 0–1.5 Table 13.4 Typical microbial reductionsachievedby chemicalmeatdecontaminationtreatments Treatment Log reduction(APCs) Organicacids 1–3.5 Chlorine 1–2 Chlorinedioxide 1–2 Trisodiumphosphate 1–3 Ozone 0.5–3 Hydrogenperoxide 2–3 274 Meat processing other countriesmay be required just to maintain current export markets.In responseto American policy, Australian and New Zealand plants are also investigating anddeveloping anti-microbial systems. It is debatablewhetherconsumerswill bewill ing to payextrafor saferfood. They logically believe that the food is alreadysafe.Processesthat eliminate pathogensshouldalso produce a substantial reductionin thenumberof spoilage organismsandhencean extensionof storagelife. This will help the economics of food production, allowing longer production runs,delivery to more distant markets,andreducedwaste.However, theintroduction of surfacepasteurisation systems does not directly improve profitability by cost savingsor increased throughput. Consequently, despitethe obvious advantages to the industry as a wholeandtheconsumer, it will beintroducedonly if it is cheap,reliableandhas low running costs.Atmosphericsteamsurfacepasteurisation hasthepotential to meetthese requirements. The majority of previousstudiesinto surfacedecontamination techniques havebeenconducted by laboratory-basedmicrobiologists interestedmainly in the effects of such treatments on specific bacteria.This research cannot be successfully scaled up to industrial usefulness becauseof the engineering problems in recreating the effective conditions asusedin the laboratory in an industrial environment. Involving food engineers and skilled microbiologists from theoutsethassignificantly greaterchanceof successful scaleup.Engineers building thelaboratoryequipment will befully awareof theconditionsusedand by direct interaction with microbiologists, have complete knowledge of the bactericidal effects. Becauseof the close collaboration and awarenessof the other disciplines’ limits, the construction of effective largescale equipment is possible. Particularengineeringchallengesexist in thedevelopmentof handlingsystems for nonlaboratorydecontaminationtreatmentof meats.For treatmentsto be effective,all surfacesneedto beexposedto thesteamenvironment.This requires non-contactor minimal-contacthandlingsystems.Most foodproductsaredelicate andrequiregentlehandlingto avoidbruisinganddamage.Handlingsystemsmust alsointegrateinto theindustrialline andthethroughputratemustbeequivalentto currentproductionrates.The handlingandtransportsystemswill differ for each producttype andwill be influencedby the treatmenttimesrequired. The main aim should be to concentrate on pathogens and harmful microorganismson real food surfaces. Typical spoilage organisms are less hardythanpathogens. Reductions in spoilage microorganismsshouldbeseenas a beneficial ‘ side-effect’ of pathogen destruction conditions. Since food poisoning results from ingestion of an infectious dose of pathogens, the absolute levelsof microorganismsremaining on productsafter treatmentshould be usedas the main measureof success. However, inoculation microbiology may be usedto evaluateprocess parameterrelationshipsfor specific products within eachscaleof processingsystem. Wherework hasbeendonewith realfood, it hasoftenlooked at reductionsin inoculated bacteriallevels as the measureof effectiveness. Whilst inoculation New developmentsin decontaminating raw meat 275 microbiology allows therelative effectivenessof differentprocessesandprocess variations to be evaluated, it is not a true representation of ‘real-world’ microorganisms.Inoculatedmicroorganisms areusually at much higher levels, differently attached, and in differing growth stages from microorganisms typically found on a food product during an industrial production process. Whilst inoculation microbiology is of usein developing equipment,more trials should be carriedout usingnaturallyoccurring contamination. Whilst this will involve greater experimentaleffort, the resultswill bedirectly applicableto the industrial problembecausenatural contamination on food will be considered at the technologydevelopment stage. In conclusion,any decontamination systemfor meatadoptedin the EU will dependon a perceivedneedby governmentandfood retailers,andwill probably require changes to current legislation. The EU Scientific Committee on Veterinary measures relating to Public Health havepublished views regarding decontamination for poultry carcasses(EU, 1998). It is probable that any decontamination systemfor redmeatwill needto addressthe recommendations of this report.The

Committee recommended that: 1. Antimicrobial treatmentshouldbe usedonly aspart of an overall strategy for pathogencontrol throughoutthe whole production chain. 2. Before any decontamination compoundor decontamination technique is authorisedfor useit shouldbe fully assessed. 3. The person/company proposing such a decontamination compound or decontamination techniquemustdemonstratethat all aspectsarecovered. 4. The person/organisation using a decontamination compoundor decon- tamination techniquemustdemonstratethat effectivecontrol of parameters critical for efficacy and safeuseare in place and that good practice and appropriateHACCP plansare implemented. 5. Basedon theconclusionsof their report,a frameworkis establishedfor the assessmentof decontaminationcompoundsor decontamination techniques proposed. 13.8 Sourcesof further information and advice An extensivereviewof decontaminationhasbeenpublished by JamesandJames (1997)at the University of Bristol andregularupdatesmade in 1999and2000. Goodgeneral reviewsof decontaminationandcontamination issueshavebeen published in recent yearsby Bolder (1997), Corry and Mead (1996), Dorsa (1997), Sofos et al., (1999), Bjerklie (2000). An overview of contamination and decontamination issuesinvolving poultry meathasbeendiscussed by Smulders (1999). Useful booksinclude those editedby Gould (1995), Smulders (1987), andEllerbroek(1999). Reviews of specific subjects include Jeyamkondanet al., (1999) on pulsed electric field processing,Kim et al., (1999)on ozoneapplications andMertens 276 Meat processing and Knorr (1992) and Palmieri et al., (1999) on non-thermal preservation methods(suchas pulsedelectric fields, pulsed light and oscillating magnetic fields). 13.9 References ANDERSON, M E and MARSHALL, R T (1989), ‘Interaction of concentration and temperature of acetic acid solution on reduction of various species of microorganisms on beef surfaces’, Journal of Food Protection, 52(5), 312–315. ANDERSON, M E, MARSHALL, R T, STRINGER, W C and NAUMANN, H D (1979a), ‘Evaluation of abeefcarcasscleaningandsanitisingunit’, Presentedat the 1979SummerMeeting of the ASAE andCSAE, PaperNo. 79-6014. ANDERSON, M E, MARSHALL, R T, STRINGER,W C and NAUMANN, H D (1979b), ‘Microbial growthonplatebeefduringextendedstorageafterwashing and sanitising’,Journal of Food Protection, 42(5), 389–392. ANDERSON,M E, NAUMANN, H D andCOOK,N K (1984),‘Design specificationsof a red meat carcasswashing and sanitising unit’, Presented at the 1984 Winter Meeting of theAmericanSociety of Agricultural Engineers,Paper No. 84-6546. BAILEY, C (1971), ‘Spray washing of lamb carcasses’, Proceedingsof the 17th European. Meeting of Meat Research Workers, Bristol, PaperB16, 175– 181. BELL, R G (1997),‘Distribution andsourcesof microbial contamination on beef carcasses’, Journal of AppliedMicrobiology, 82, 292–300. BELL, R G, HARRISON, J C L andROGERS,A R (1993),‘Preliminary investigation of the distribution of microbiological contamination on lamb and beef carcasses’, MIRINZ Technical Report927. BIEMULL ER, G W, CARPENTER, J A and REYNOLDS, A E (1973), ‘Reduction of bacteriaon pork carcasses’,Journal of Food Science, 38, 261–263. BJERKLIE, S (2000),‘Interventionoverview’, Meat Processing: North American Edition, June,94, 96–97. BOLDER,N M (1997), ‘Decontaminationof meatandpoultry carcasses’,Trendsin Food Science& Technology, 8(7), 221–227. CACCIARELLI, M A, STRINGER,W C, ANDERSON, M E and NAUMANN, H D (1983), ‘Effects of washingandsanitising on bacterialflora of vacuum-packaged pork loins’, Journal of Food Protection, 46(3), 231–234. CARLEZ, A, ROSEC, J, RICHARD, N andCHEFTEL, J (1994),‘Bacterial growth during chilledstorageof pressuretreatedmincedmeat’,Lebensmittel-Wissenschaft und Technologie, 27, 48–54. CHARLEBOIS,R, TRUDEL, R andMESSIER,S (1991), ‘Surfacecontamination of beef carcassesby faecal coliforms’, Journal of Food Protection, 54(12),950– 956. CORRY,J E L andMEAD, G C (1996), Microbial Control in the Meat Industry: 3. New developmentsin decontaminating raw meat 277 Decontamination of Meat, Concerted Action CT94–1456, University of Bristol Press. CUNNINGHAM, F E (1978), ‘The effect of brief microwavetreatment on numbers of bacteriain freshchickenpatties’,Journal of FoodProtection, 57, 296– 297. 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(1999)COSTAction 97 – Pathogenic microorganismsin poultry and eggs.8. NewTechnology for Safeand Shelf-stable Products, Luxembourg: Off ice for Off icial Publ ications of the European Communities. ELLERBROEK, L I, WEGENER, J F and ARNDT, G (1993), ‘Does spray washing of lamb carcasses alter bacterialsurface contamination?’, Journal of Food Protection, 56:5, 432–436. EUROPEANUNION (1998), Benefitsand Limitations of Antimicrobial Treatments for Poultry Carcasses, Reportof the Scientific Committeeon Veterinary Measuresrelating to Public Health,30 October 1998. EVANS, J A (1999),‘Novel decontamination treatmentsfor meat’, in Ellerbroek, L, COSTAction97 – Pathogenic micro-organismsin poultry andeggs.8. NewTechnology for Safeand Shelf-stableProducts, Luxembourg: Office for Official Publicationsof the European Communities,14–21. EVELEIGH, K (2000), ‘Carcassdecontamination’, Meat and Poultry 2000 – Seminar1, CampdenandChorleywood Food ResearchAssociation,UK, 17 July 2000. 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JAMES,C, NICOLSON,M andJAMES,SJ (1999),Review of microbial contamination and control measures in abattoirs, FRPERC, University of Bristol. JAMES, C, GÖKSOY, E O, CORRY, J E L and JAMES, S J (2000a), ‘Surface pasteurisation of poultry meat using steam at atmospheric pressure’, Journal of Food Engineering, 45, 111–117. JAMES, C, THORNTON, J A, KETTERINGHAM, L and JAMES, S J (2000b), ‘Effect of steamcondensation, hot water or chlorinated hot water immersion on bacterial numbers and quality of lamb carcasses’, Journal of Food Engineering, 43, 219–225. JEYAMKONDAN, S, JAYAS, D S and HOLLEY, R A (1999), ‘Pulsed electric field processingof foods:A review’, Journal of FoodProtection, 62(9), 1088– 1096. KELLY, C A, DEMPSTER, J F and MCLOUGHLIN, A J (1981), ‘The effect of temperature, pressureandchlorine concentration of spray washing water on numbers of bacteria on lamb carcasses’ , Journal of Applied Bacteriology, 51, 415–424. KIM, JG,YOUSEF,A E andDAVE, S (1999), ‘Application of ozonefor enhancing the microbiological safety and quality of foods: A review’, Journal of Food Protection, 62(9), 1071–1087. KLOSE, A A, KAUFMAN, V F, BAYNE, H G andPOOL,M F (1971),‘Pasteurisationof poultry meat by steam under reducedpressure’, Poultry Science, 50, 1156–1160. LEE, R M, HARTMAN, P A, OLSON, D G andWILLIAM S,F D (1994), ‘Bactericidal and bacteriolytic ef fects of selected food-grade phosphates, using Staphylococcusaureusas a model system’, Journal of Food Protection, New developmentsin decontaminating raw meat 279 57(6), 276–283. MERTENS,B and KNORR, D (1992) ‘Developmentsof non-thermal processesfor food preservation’,Food Technology, 46(5), 124–133. MORGAN, A I, GOLDBERG, N, RADEWONUK, E R andSCULLEN, O J (1996a), ‘Surface pasteurization of raw poultry meatby steam’,Lebensmittel -Wissenschaft und Technologie, 29, 447–451. MORGAN, A I, RADEWONUK, E R and SCULLEN, O J (1996b), ‘U ltra high temperature,ultra short time surfacepasteurisation of meat’, Journal of Food Science, 61(6), 1216–1218. NUTSCH, A L, PHEBUS, R K, SCHAFER, D, PRASAI, R K, UNRUH, J, WOLF, J and KASTNER, C L (1995), ‘Use of steam for reduction of Escherichia coli O157:H7, Salmonel la typhimurium and Lister ia monocytogenes populations on raw meat surfaces’, Food Safety Consortium, Annual Meeting, Agenda,Presentations and Progress Reports, 25–26 October, KansasCity, Missouri, 102–108. NUTSCH, A L, PHEBUS, R K, SCHAFER, D, WOLF, J, PRASAI, R K, UNRUH, J and KASTNER, C L (1996), ‘Steam pasteurization of beef carcasses’ , Cattlemen’sDay 1996,Report of Progress756, Agricultural Experiment Station, KansasStateUniversity, 1–3. 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‘Non-thermal methodsof food preservationbased on electromagnetic energy’, Rivista Italiana EPPOS, 27, 5–11. PATERSON,J L, CRANSTON,P M andLOH, W H (1995),‘Extendingthe storageli fe of chilling beef: microwaveprocessing’, Journal of MicrowavePowerand Electromagnetic Energy, 30(2), 97–101. PHEBUS,R K, NUTSCH,A L andSCHAFER, D E (1996a), ‘Laboratory andcommercial evaluation of a steampasteurisation process for reduction of bacterial populations on beef carcasssurfaces’, Proceedings of the 49th Annual Reciprocal Meat Conference, 49, 121–124. PHEBUS,R K, NUTSCH,A L, SCHAFER,D E andKASTNER,C L (1996b), ‘Eff ectiveness of a steampasteurisation process for reducing bacterial populationson beef carcasses in a commercial slaughter facil i ty’ , Food Safety Consortium, Annual Meeting, Agenda, Presentations and Progress Reports, October 21–22,KansasCity, Missouri, 198–202. PHEBUS, R K, NUTSCH, A L, SCHAFER, D E andKASTNER, C L (1996c),‘Effectiveness of steampasteurisationat reducingnaturallyoccurringbacterialpopulations at five anatomicallocationson commerciallyslaughteredbeef carcasses’, 280 Meat processing Food Safety Consortium, Annual Meeting, Agenda, Presentationsand ProgressReports, October21–22,KansasCity, Missouri, 203–206. PHEBUS, R K, NUTSCH, A L, SCHAFER, D E and KASTNER, C L (1997a), ‘Steam pasteurization to reduce bacterial populations on commercial ly slaughtered beef carcasses’,Cattlemen’s Day 1997, Report of Progress 783,Agricultural Experiment Station, KansasStateUniversity, 4–5. PHEBUS,R K, NUTSCH,A L, SCHAFER, D E, WILSON, R C, RIEMANN, M J, LEISING, J D, KASTNER, C L, WOLF, J R and PRASAI, R K (1997b), ‘Comparisonof steam pasteurisation and other methodsfor reductionof pathogenson freshly slaughteredbeefsurfaces’,Journal of Food Protection, 60(5), 476–484. PHEBUS,R. K., TRUAX, A., SPORING,S., RUEGER, S. A., SCHAFER, M., BOHRA, L. K., HARRIS, L. and RETZLAFF, D. D. (1999) Antibacterial effectivenessof a second generation steam pasteurization system for beef carcass decontamination. Cattlemen’s Day 1999, Report of Progress 831, Agricultural ExperimentStation, KansasStateUniversity. 4–6. REAGAN, J O, ACUFF, G R, BUEGE, D R, BUYCK, M J, DICKSON, J S, KASTNER, C L, MARSDEN, J L, MORGAN, J B, NICKELSON II, R, SMITH, G C and SOFOS,J N (1996), ‘Trimming and washing of beef carcassesas a method of improving the microbiological quality of meat’ , Journal of Food Protection, 59(7), 751–756. REYNOLDS, A E andCARPENTER, JA (1974),‘Bactericidal propertiesof aceticand propionic acidsonporkcarcasses’, Journal of Animal Science, 38(3), 515– 519. SMITH, G (1996), ‘Steam is the theme in the war on pathogens’, Meat Processing: North American Edition, 35(2), 32–34. SMITH, M G (1992), ‘Destruction of bacteria on fresh meat by hot water’, Epidemiology and Infection, 109, 491–496. SMITH, M G andDAVEY, K R (1990), ‘Destruction of Escherichia coli on sidesof beefby ahot waterdecontaminationprocess’, FoodAustralia, 42(4),195– 198. SMULDERS, F J M (ed.)(1987), ‘Eliminationof PathogenicOrganismsfrom Meat and Poultry’, Elsevier: Amsterdam-New York-Oxford. SMULDERS, F JM (1995),‘Preservationby microbial decontamination;thesurface treatment of meatsby organic acids’, in Gould, G W, New Methodsof Food Preservation, Elsevier: Amsterdam-New York-Oxford, Chapter 12, 253–282. SMULDERS, F JM (1999),‘Contaminationanddecontaminationof foodsof animal origin, with special reference to poultry meat’, in Ellerbroek, L, COST Action 97 – Pathogenic micro-organisms in poultry and eggs.8. New Technologyfor Safeand Shelf-stableProducts, Luxembourg: Office for Official Publicationsof the EuropeanCommunities, 4–13. SOFOS,J N, BELK, K E andSMITH, G C (1999),‘Processesto reducecontamination with pathogenicmicroorganismsin meat’, 45th International Conference of MeatScienceandTechnology (ICoMST’99), Yokohama,Japan, 45(2), 596–605. New developmentsin decontaminating raw meat 281 STERMER, R A, LASATER-SMITH, M and BRASINGTON, C F (1987), ‘Ultraviolet radiation – an effective bactericide for fresh meat’, Journal of Food Protection, 50(2), 108–111. ZHANG, Q, CHANG, F -J, BARBOSA-CÁNOVAS, G V and SWANSON, B G (1994), ‘Inactivation of microorganisms in a semisolid model food using high voltage pulsed electric f ields’ , Lebensmittel -Wissenschaft und Technologie, 27, 538–543. ZHANG, S and FARBER, J M (1996), ‘The effectsof various disinfectantsagainst Listeria monocytogeneson fresh-cutvegetables’, Food Microbiology, 13, 311–321. 282 Meat processing 14.1 Introduction The meat industry has trailed far behind other industries as far as process automation is concerned. The reason is that until recently the biological variation in the raw material made it very difficult to automate. However, the development of faster computer techniques, more sophisticated sensors and more advanced vision techniques has facilitated progress of automation in the meat industry during the last decade. In many industrialised countries there is an increasing shortage of labour. Compared to most other industries the working environment in the meat industry is characterised by noise, draft, humidity, cold and repetitive work under pressure. Dealing with the slaughtering of animals, separation and movement of the various components of the carcass, and disposal of waste is also both physically demanding and, for some, unpalatable. The meat industry is not, therefore, very attractive for prospective employees, especially young people. To overcome potential labour shortages and get better returns from its existing workforce, the meat industry has come under increasing pressure to automate the most labour-intensive parts of meat production. These pressures have been increased in Europe by relatively static overall consumption of meat over the last decade and the increasing pressure on margins in meat processing. Automation, however, always requires a high level of investment. A reasonable payback time is realistic only in industries with high production volumes and high labour costs. There is the additional risk that automation creates more repetitive and uninteresting work, exacerbating potential labour shortages. Profitable automation of processes in the meat industry requires a certain degree of uniformity in the raw material. This is the main reason why automation has come much further in the pig, poultry and lamb industries than in 14 Automated meat processing K. B. Madsen and J. U. Nielsen, Danish Meat Research Institute, Roskilde the beef sector.Automation has the potential to createend products of more uniform quality. If machineryis properlycleanedandsterilised,it alsobecomes possible to producesaferproducts.However,if these high hygienicstandardsare not maintained,automatedproduction may severelycompromisemeatsafety. In beef production the first use of robotic equipmentwas in splitting a complete carcassinto carcasssides.A numberof manufacturersproducesuch equipmentwhich replacesthisparticularlyarduousmanualprocess.However, the performanceof such equipmentis still not satisfactoryin termsof theaccuracyof splitting the carcassdown the centre of the spinal column, and the hygiene problemsassociatedwith the depositionof bonedust and other detrituson the ediblesurfacesof thecarcass.Theseproblemshavebeenhighlightedrecentlyby theBSEcrisis in Europe.During the1980sa very comprehensiveandambitious Australian developmentproject called ‘Fututech’ was startedwith the aim of automating thecompletebeefslaughteringprocess. For a numberof reasonsthis project fai led and was abandoned (Purnell , 1998). Other attempts at comprehensiveautomationof the beef slaughteringprocesshavebeenmadein theUSby theTexasBeefGroupandin theUK by theUniversityof Bristol. None of them has,however, yet resultedin commercialequipmentfor the industry (Purnell, 1998). Semi-automaticequipmentfor grading of beef carcasseshas been developedby companiesin Denmark, Germany,Australia and Canada. They are all basedon vision imageanalysis(VIA). Someof them are usedin daily productioneventhoughnoneof themhasyet beenapprovedby the EU. Automation of sheepand lamb slaughtering hasmainly beencarried out in Australia and New Zealand.The Meat Industry Research Institute of New Zealand (MIRINZ) has in particular been very active in this area. Several manual operations have beenmechanised,improving both process efficiency andhygiene,thoughlambproductionis still not fully automated(Templeret al., 1998).In contrast,automatedslaughtering andpreparation of poultry is carried out at very high line speeds,thoughit requiresbirds to be of uniform sizeand shape. Recentlyresearch using sensor-driven robotic techniquesto improve the cutting processhasbeencarriedout in UK andUS,althoughtheseprocessesare not yet commercialised(Purnell,1998). This chapter will , however, deal mainly with the automation of pig slaughtering processes. Denmark has for many years been a leader in the automation of primary and secondaryprocesses in pig slaughtering. This has beenpartly due to high labour costs,but is alsodueto theco-operativestructure of the Danish meat industry which has enabledjoint financing of the high developmentand investment costsof processautomation. 14.2 Current developments in robotics in the meat industry Standard robotshavebeenin usefor manyyearsin manyindustries.However, the meat sectorhasbeenreluctantto introducestandard industrial robots for a number of reasonsincluding: 284 Meat processing • the harshnessof the environment in the meatindustry • the speed,reliability andcostof the robots • the complexity of the processes involving handlingbiological materials. The use of dedicated automatic equipment has thereforebeen the dominant feature for themeatsector.However, standard modernmulti-axisrobots,usedin combination with advancedvision andhigh-speeddigital video techniques,have providedthe foundationfor developing dedicated automatic machinery for the meatindustry.Thesetechniqueshavespeeded up the developmentprocessand helpedto find solutionswhich were simply not possible a few yearsago. During the last few years industrial robotswith namessuch as ‘Clean Room Robot’, ‘Envirobot’ and‘Shiny Robot’ havebeen introducedto themeat industry. Industrial ResearchLtd., New Zealand, hasmarketing the Envirobot for handling organic products in harshenvironmentssuch as the food industry. It has been developed especiallyfor slaughterhousesin Australia andNewZealand,whereit is usedfor the critical so-called Y-cuts in connectionwith dehiding and cutting of lamb carcasses and for sawing through the breastbone on cattle carcasses. The Envirobot is madeof stainlesssteeland resistsharshcleaningmaterials and the corrosivechilled environmentin slaughterhouses(Purnell,1998). TheGermancompanyKUKA Roboter GmbHhaspatenteda cabinetfor their robots,which is capable of resisting the harshslaughterhouseenvironment. At presentit is installedat the Gilde HedOpslaughterhousein Norway andat the FACCSA slaughterhousein Spain. The robot, which performscertaincutsand jet-ink printing on pig carcasses,is guided by a vision camera. The KUKA robot seemsto providea cheapersolutionto theenvironmental problemspresentedby

slaughterhouseconditions than the Envirobot (Khodabandehloo, 1999). The German company imt-Peter Nagler GmbH has patenteda robot packaging system‘Ulixes Sortierer’ for high-speed packagingof hot dogs, bacon and similar products.This systemshould havegoodmarket penetration asit replaces what was a time-consuming and arduousmanual operation with significant potential hygiene risks (Wolf, 1999). Traditional industrial robots are increasingly usedfor packaging and palletisation in the food industry because productsat thatstagehavea very well definedshapeandareeasyto handlewith traditional robot programming solutions. 14.3 Automation in pig slaughtering Table 14.1 provides an overview of the handling of slaughter pigs from transportationof thelive animalsthroughtheslaughterprocessto thepackaging of thefinal products.Thepre-slaughterhandlingof theanimals is importantboth for animal welfare and for ensuring good meatquality. The transportation of animalsto the slaughterhousehasto be performedasgently aspossible. Often the pigs are delivered from the farmer in the samegroupsin which they are reared.At themostadvancedslaughterhousesthepigsareheldin thelairageand Automated meat processing 285 driven to stunningin these groups, thus preventing fighting and stress. CO2- stunning is becoming moreandmore widespreaddueto advantages with respect to animalwelfare andmeatquality. Equipment for automatic CO2-stunning of groupsof 5–6pigs, developedby theDanishMeatResearchInstitute (DMRI), is being installed in manyEuropeanandAmerican slaughterhousesat themoment (Christensenet al., 1997). Shackling and sticking of the stunned animalswill probably neverbe fully automated,as the animals are still alive at the time of these operations.Apart from thesetwo operationsandthegambrelling operation,all otheroperationson Table 14.1 Schematicoverviewof the pig slaughterprocess Processsection Main subprocesses Live animalhandling Transportationto slaughterhouse Unloadingof pigs Veterinaryantemorteminspection Restperiod in lairage Transferto stunning CO2 stunning/electricalstunning Sticking andbleeding Shackling Sticking andbleeding U N Surfacetreatment Scalding C Deshackling L Mechanicaldehairing E Gambrelling A Singeing N Rind scraping/polishing C Eviscerationandtrimming Carcassopening L Removalof secondaryorgans E Removalof stomachandintestines A Removalof pluck N Preparationfor splitting Carcasssplitting Inspectionandquality Veterinaryinspectionof carcasses measurements andcuts Carcassweighing Carcassclassification Downstreamprocesses Carcasschilling Sorting into quality groups Storageandtemperature Equilibration Secondaryprocesses Carcasscutting Boning andtrimming of cuts Packaging 286 Meat processing theuncleanslaughterline(scalding, singeing, scraping andpolishing) havebeen carried out automatically for severalyears. Dehiding, which is rarely done outsidethe Far East,is only partly automated. Carcasssplitting eitherby choppingor by sawinghasbeen automatedfor many years.A few years ago the Dutch company STORK MPS launchedthe F-line modular series of dedicated robots,which are now operational in a numberof countries.They havebeen installedin slaughterhouseswith line speeds of 600pigs perhour(or more)in asingleline layoutor 1200pigsperhour in adoubleline (Van Ochten,1999).In theF-lineconcept,thefollowing processeshavebeenautomated: • cutting of the pelvic symphysis • openingof the abdomen andthe thorax • removalof the fat end • neckcutting • removalof the leaf lard. The Danish companySFKDanfotechhas, in co-operationwith the Danish Meat ResearchInstitute (DMRI), developed a seriesof dedicated robots for automation of slaughterline processes. The robot series is manufactured as separate modules, each robot having its separatehydraulic station and PLC control. All robotshavecapacities for between360 and400 carcassesper hour andmaybeinstalled separately or asa line dependenton therequirementsof the slaughterhouse.The seriesof robotsconsistsof: • a measuringunit to determine the lengthof the pig carcass • throatcutter • fat enddropper andhamdivider • carcassopener • evisceration equipment • equipment for back finning • a carcasssplitting machine. All therobotsareoperationalin anumberof slaughterhouseseitherindividually or as more or less completelines (Anon., 2001). Automatic weighing of dressed carcassesin connectionwith carcassclassification is performed either semi- automaticallyor fully automatically(ultrasound,vision or opticalprobes)on most modernslaughterlines.Theonly two fully automaticclassificationsystemsarethe Danish CarcassClassificationCentredevelopedby the DMRI and the AUTO- FOM systemdevelopedby theDanishcompanySFK-Technology(Madsenet al., 1992;Brandscheidet al., 1997). 14.4 Casestudy: the eviscerationprocess The eviscerationprocess,which involves the cutting and removal of the pig’s internal organs,is one of the most demandingoperationson the slaughterline. Even when slaughterhousestry to easeindividual operatorstrain through job Automated meat processing 287 rotationanda practicaldesignof thework place,intestineandpluck removalare still the mostdifficult processesto manon the slaughterline.Until recentlythese operationshavebeencarriedout manuallyasno automaticequipmenthasexisted. Manual eviscerationat Danishslaughterlines with capacitiesof 360–400pigs perhouris normally carried out by threeoperatives. Thefirst operativecutsfree the intestinal tract from the abdominal cavity and then separates the pluck set andthe intestinal tract insidethe carcassby cutting the oesophagusclose to the stomach. Finally he lifts the intestines weighing about 10kg into a conveyor tray. The secondoperative loosens the diaphragm and leaf fat. The third operative cutsthepluck setloosefrom thethoracic cavity andneckandlift s the pluck setweighingabout5kg onto a conveyorhook.The evisceration process, particularly the cutting of the oesophagusclose to the stomachinside the carcass,risks causing contamination of the carcasswith pathogenicbacteria. Both from a working environment, a cost and a hygienepoint of view, the eviscerationprocessis anobviouscandidatefor automation. This hasbeendone successfully by the DMRI in co-operation with the Danish companySFK- Danfotech. The automatic evisceration equipment (Fig. 14.1) is capable of handling 360 carcasses per hour including the necessary cleaning and disinfection.The pluck setandthe intestinal tract are removedtogether by the robot, allowing separation to be done manually outside the carcass, thus improving hygiene comparedwith existing manual methods. The equipment also eliminatesthe heavywork of li fting the intestinal tract andthe pluck set. Basically, the automatic evisceration system consists of a measuring station andahandlingstation. Themeasuring stationmeasurestheposition of theelbow of thepig carcass, which is anatomically closeto wherecuttingoperationsoccur, allowing the handling station to identify where to cut into the carcass.The measuring station is positioned on the slaughter line prior to carcassopening. The handling stationcontainsseventools (asshownin Fig. 14.1): 1. A thoraxopener. 2. Units for fixing the carcass. 3. An integrated tenderloin cutter, resistance bracketand lung loosener. 4. Conveyor systems for transporting the pig carcassinto and out of the handlingstation. 5. A special unit cutting the intestinal attachment to the spine and cutting throughthe diaphragm at the spine. 6. An intestine shovellifting up the intestines. 7. Bracketsfor detachment of the diaphragm and leaf fat. A motorised knife integrated in eachbracketcuts throughthe diaphragm. A completecyclefor thehandling of acarcassconsistsof thefollowing steps: 1. The carcassarrivesat the handlingstation. 2. The carcassis pushedinto the machine by the conveyor system(4), data from the measuring stationare transferredto the handling station and the tools takeup their startingposition. 288 Meat processing 3. The carcassis held in the fix ing unit (2). 4. The intestineshovel(6) lifts up the intestineshangingout from the opened carcasstherebyexposing the insertion points for the leaf fat brackets. 5. The leaf fat brackets(7) arepushedinto the carcassandopened. 6. The thorax is openedby the thoraxopener(1). 7. The intestine shovel(6) is withdrawn.Intestineshangingout will fall down throughthe opening between the leaf fat brackets. 8. The knivesbuilt into the leaf fat brackets cut free the diaphragm. 9. The backcutter(5) is moved along thespineandpenetratesthediaphragm. The backcutteris thenmoved upwardsalong thespine andcutsthroughthe diaphragmandthe connectivetissuebetween spineandthe intestinal tract. (Operations9 and10 arecarriedout simultaneouslywith operations4 to 8). Fig. 14.1 Automaticeviscerationsystem. Automated meat processing 289 10. The tool containing the tenderloin knife (3) moves downwards. Having passedthe hind legs the knife is turnedin. The knife cuts the tenderloins alongthe spine.The knife is movedout. The tool is now placed on top of the diaphragm with a predetermined force thereby acting as resistance during the following leaf fat loosening. 11. The leaf fat brackets (7) are movedupwardsinside the pig. The brackets passbetween the leaf fat andabdominal wall therebydetaching the leaf fat completely. 12. The tool (3) continuesdownwards into the thoracic cavity of the carcass therebyloosening possible adhesions between the lungs and the thoracic wall. At thesametime thethorax is openedfurtherby thethoraxopener(1) to facilitate the detachment process. 13. Thetool (3) is taken out horizontally from thethoracic cavity of thecarcass, pulling the organs out. 14. The thorax opener(1) and the fixing units (2) are moved back to their startingpositions. 15. The carcassis pulled out of the handlingunit. 16. The tools are washedfirst in cold and then in hot water before the next carcassarrives. As mentionedpreviously, the machine is capable of handling360carcassesper hour. This implies a total operation cycle of 10 secondsfor eachcarcass.At presentthecutting anddivisionof thepluck setinto theindividual organs is also in the processof beingautomated by the DMRI. This is a difficul t taskas the pluck set is not very well defined. Automatic equipment for this purposeis expected to be availableby 2004. 14.5 Automation of secondaryprocesses The main secondary processesare cutting and boning of carcasses.These processesinclude: • carcasscutting • cutting of the middle • boning of the fore-end • hind-leg boning • boning andtrimming of bellies • boning andtrimming of the loin. 14.5.1 Carcasscutting Af ter chill ing andtemperatureequalisation for about20 hoursthecarcasshasa temperatureof approximately 2ºC. For further processing the carcassis most often cut into the primary cuts:hind leg, middle andfore-end. Fully automatic equipment performing this operation was developedby the DMRI and is 290 Meat processing marketed by the Danish company ATTEC. The equipment consists of a conveyor andthreestations: 1. a laying-down station 2. a measuring station 3. a sawingstationwith a hind leg sawanda fore-end saw. At the laying-downstationthe two half carcassesarepositionedhorizontally on a conveyor. Simultaneously the gambrel is taken off andthe hind feet aresawn off. Theconveyor bringsthecarcassto themeasuring stationwhereahooktakes hold of the pubic boneof eachhalf carcassand

brings it to a fixed position relativeto the hind leg saw.During this movement the position of theelbow of the two half carcassesis recorded. Theconveyor afterwardstakesthecarcassto the sawingstation.During transportto the sawingstation the fore-end saw is positionedaccording to therecordedpositionof theelbowof thecarcass.At the sawingstationthe half carcasses are divided into fore-ends,middlesand hind legs. 14.5.2 Cutting of the middle In many current slaughterlines the rib topsarecut off manually with a circular sawandtheloin andthebelly aresubsequently dividedmanually by abandsaw. Theseprocesses,however,cansoonbeautomatedfully. TheCanadiancompany LeBlanc is marketing equipment for splitting the loin and the belly automatically. QuebecIndustrialResearch Centre (CRIQ) recentlypresenteda prototype for cutting off the rib tops automatically (RobocutTM). During 2002 ATTEC will market equipmentfor cutting off the rib topsanddividing the loin andthe belly automatically. This equipment(Fig. 14.2)hasbeendevelopedby the DMRI. The equipment consistsof: • a conveyor • a measuringstation • a sawing station. Theconveyor is equippedwith a graspingdevice,which pulls therib topsout to their full length.This straightens out the backbone, simplifying the subsequent sawing off of the rib tops. After fix ing in the conveyor, the middle passes throughmeasuring stations,which measuresthe length and any inaccuracy in theearlier carcasssplitting. Basedon these measurements, thesawsareadjusted to cut off the belly from the loin andsubsequentlycut off the loin from the rib tops. 14.5.3 Boning of the fore-end Boning of fore-ends hasmost often beendonemanually. However, the Dutch companySTORK MPS is marketing equipmentfor press boning of fore-ends. The equipment has a tool consisting of two halves with indentations Automated meat processing 291 corresponding to the bonesin the fore-end. The fore-endis placedbetween the two halves.Thesearepressedtogether andthe meatis squeezedoff the bones. The disadvantageof usingthis methodis that thetexture of themeatis changed, andthemeatcancontainsplintersof bone.As a result,theuseof this equipment hasnot becomewidespreadin the industry. Against this backgroundthe DMRI hasdevelopedequipment which cancut off the riblet and neck-bone automatically from fore-ends (Fig. 14.3). The Townsendcompany will market the equipment during 2002. The equipment operatesasfollows: • a conveyor, equippedwith a grasping devicesimilar to that described in the previoussection,catchestheneck-boneof the foreend andstraightensit out to simplify the later removalof the neck-bone • the fore-endthenpassesa number of measuring stations andknives • the first knife loosensthe meatbehindthe neckbone • the next knife loosensthe deeperportion of the neck-bone • the riblet is cut free by a sword-like knife mountedin a 3-axis robot • thefore-end now passes a saw,which cutsoff theriblet andsaws throughthe first neck joint • finally, themeatis pulledoff theneckbonebeforethelastknife cutstheneck bonefree. The remaining processes of removing the shankbones,humerusand shoulder blade will becarried out by equipment which is currently beingdevelopedat the DMRI and is expected to be marketed by the middle of 2004. Fig. 14.2 Automatedsecondaryprocesses:cutting of the middle. 292 Meat processing 14.5.4 Hind leg boning Boningof hind legshasto bedonevery precisely asit is themostexpensive cut. For this reasonit is still most often done manually. However, in 1998 the JapanesecompanyMYCOM at the IFFA exhibition in Frankfurtdemonstrated equipment called Hamdas, which boneshind legsautomatically. However,this equipment has a low yield and it will probably take someyears before this processis completely or partly automated. 14.5.5 Boning and trimm ing of bellies Boningof belliesis alsomost oftencarriedout manually. It mayalso takeyears before this process is completely or partly automated. However, CRIQ has developedequipment which can cut the ribs off the belly by using a visionguidedrobot.Trimming of belliesis alsostill normally carriedout manually. At the beginning of 1990 the Danish companyLumetech marketed equipment which trimmed bellies by using water jets and vision guided robots, but the systemneverachievedwidespreadusein industry becauseof its high price. 14.5.6 Boning and trimm ing of the loin Boningof loins is anotherpredominantly manual process,particularly asloin is an expensive cut requiringa high degreeof accuracyandskill. It will probably takeanumberof yearsbefore this processis completelyor partly automated.Fat Fig. 14.3 Automatedsecondaryprocesses:boningof the fore-end. Automated meat processing 293 trimming of loins has, however, been automated for a number of years. A number of companiesare marketing so-calledloin pullers where the loin is pulled through a fixed shaped knife. The DanishcompanyCARNITECH has improvedthis concept by controlling theshapeof theknife with a computer. On the basisof information from measuring the thickness of the fat, a computer adjusts the position and shapeof the knife cutting off the fat, making the fat trimming of the loin more precise. 14.6 Future trends Within the next few years slaughtering of pigs aswell assecondaryprocessing will be partly automated.Fig. 14.4shows the layout of an automated slaughter line of the future.Thereare,however, a numberof issueswhich still needto be resolved beforeautomation canprogressto this point. 14.6.1 Automation and hygiene In automated, high-speedproduction,sterilisation of toolsandequipment will be of great importance in preventingcrosscontamination. This is an areawhich requiresmajor attentionin the future. In many cases the presentdisinfectionof machinerybetween theprocessingof individualproducts is not sufficient. More attention hasto bepaid at the designstageto theeaseof cleaning the tools that get into contactwith the products. Often a dedicated disinfectionsystemhasto be usedfor eachindividual type of equipment.Applicationof severalstepsfor washing and disinfection of automatic equipment has proved to be very effective. In addition, varying water pressures and temperatures helps to optimise cleaning.A possibility might also be application of lactic acid for disinfection of especially exposedtools. This disinfectionmethodis, however, not yet permittedeverywhere. 14.6.2 Automation and management With the increased automation of previously manual operations at slaughterhouses,it is also necessaryto focus on the new challengesfacedby line andsupervisory staff. Increasedautomation will influenceandchangethe currentrole of operatives,their level of responsibility andthequalificationsthey need.In the future: • Supervisorswill havefewerandmoredemanding operativeswho wantmore influence on their working situation. The supervisorwill therefore haveto spendmoretime on managementandestablishment of goodco-operationand training of the production team. • The quality of products will to a large extent dependon the automatic production equipment.Much moreattention will thereforehaveto bepaid to the surveillance and control of the automatic machineryin order to secure 294 Meat processing Fig. 14.4 Layout of an automatedslaughterline of the future. high yield andshortdowntimes.The operativeswill not only haveto monitor the automatic equipment andmakeminor adjustments, but mustalso check thequality of theproducts. This requireswiderknowledgebothfor operatives andfor productionmanagement. Automation will also change the present organisation and communication structure: • It may requireproductionteams of butchers, maintenance staff andmachine operatives working separately for the production manager.Payment of the employeeswill probablybeon a teambasis.This might easeintegrationand co-operation between the traditional trade groups, ensuring higher productivity andbetterquality of endproducts. • The supervisor will haveto act ascoachfor the productionteam. • Therewill be a requirement for fuller and more rapid communication with managementas well as a continuous dialogue with the production and maintenancedepartments. On thewhole,thechangefrom mainly manual craft-basedproduction to almost fully automated productionwill give the production management many new challenges. 14.7 Referencesand furth er reading ANON. (2001),Automatic slaughterline for pigs.Fleischwirtschaft International, March. BRANDSCHEID, W. et al. (1997), Bestimmung der Handelsklassen und des Handelswertes von Schweinchäl f ter mi t dem Gerät Autofour. Fleischwirtschaft 77(7). CHRISTENSEN, L. et al. (1997), New Danish developmentsin pig handling at abbatoirs. Fleischwirtschaft 77: 604–607. KHODABANDEHLOO, K. (1999), Advancing robots in the meat industry. Meat Automation No. 2. MADSEN,K. B. (1994),Automationin thePig Slaughterline. ECCEAMST course, September. MADSEN, K. B. et al. (1992), Fremgangsma˚de oganlag til behandling eller undusøgelseaf slagtokjoppe,Patent6295/86. NIELSEN, J. U. (1999),Automatic evisceration of pigs. Meat Automation No. 2. PURNELL, G. (1998)RoboticEquipment in theMeatIndustry.MeatScience, Vol. 49. TEMPLER, R. et al. (1998) New Automation Techniquesfor Sheepand Beef Processing,Meat AutomationNo. 2. VAN OCHTEN, S. (1999),Automation for theslaughter line. Meat AutomationNo. 2. WOLF, A. (1999),High-speedpackaging usingrobots.Meat AutomationNo. 2. ZINK, J. (1995), Application of automation and robotics to pig slaughtering. Proceedingsof 41st ICOMST. 296 Meat processing 15.1 Introduction The American Food and Drug Administration (FDA) reckons – ‘conservatively’, according to one official – that there may be anywhere between 24 and 81 million cases and 10,000 ‘needless deaths’ from food poisoning in the US every year. In England and Wales reported cases of food poisoning have increased nearly fivefold over the last decade. In addition to the human cost the economic loss in terms of working days and medical treatment in the US is between $5 billion and $6 billion. A study of one outbreak ofSalmonella enteritidisin the UK calculated that it cost the country between £224 and £321 million. Even a superficial examination of the problem reveals that temperature control is the prime factor that determines the safe distribution life of many foods including meat. Temperature control also determines the ultimate eating quality and economic yield of the product. Temperature is one of the major factors affecting microbiological growth. Microbiological growth is described in terms of the lag phase and the generation time. When a microorganism is introduced to a particular environment there is a time (the lag phase) in which no increase in numbers is apparent followed by a period when growth occurs. The generation time is a measure of rate of growth in the latter stage. Microorganisms, have an optimum growth temperature at which a particular strain grows most rapidly, i.e. the lag phase and generation time are both at a minimum. They also have a maximum growth temperature above which growth no longer occurs. Above this temperature, one or more of the enzymes essential for growth are inactivated and the cell is considered to be heat-injured. However, in general, unless the temperature is raised to a point substantially above the maximum growth temperature then the injury is not 15 New developments in the chilling and freezing of meat S.J. James, Food Refrigeration and Process Engineering Research Centre (FRPERC), University of Bristol

lethal and growth will recommence as the temperature is reduced. Attaining temperaturessubstantially abovethe maximum growth temperature is therefore critical during cooking andre-heating operations. Of most concern during storage, distribution and retail display of meatand meat products is a third temperature, the minimum growth temperature for a microorganism. As the temperature of an organism is reducedbelow that for optimum growth then the lag phaseand generation time both increase.The minimum growthtemperaturecanbeconsideredto bethehighest temperature at which eitherof thegrowthcriteria, i.e., lag phaseandgeneration time, becomes infinitely long. The minimum growth temperatureis not only a function of the particular organism but alsothetypeof foodor growthmediathat is usedfor the incubation.Although some pathogenscangrow at 0ºC, or evenslightly lower, from apracticalpointof view therisksto foodsafetyareconsiderably reducedif meat is maintainedbelow 5ºC. Meat may also become microbiologically unacceptableas a result of the growth of spoilage microorganisms.Their growth can produce unacceptable changes in the sensory quality of many foods and their rate of growth is also very temperaturedependent.The developmentof off odoursis usually the first sign of putrefaction in meat and occurs when bacterial levels reach approximately 107 per cm2 of surface area. When bacterial levels have increased a further tenfold, slime begins to appearon the surfaceand meat received in this condition is usuallycondemned out of hand.At 0ºC beefwith averageinitial contamination levels canbe kept for at least15 daysbefore any off odourscanbedetected.Every 5ºCrise in thestoragetemperatureabove0ºC will approximately halve the storage time that can be achieved. So from a spoilagepoint of view, andthe underlyingeconomic consequencesof extended storage/distribution life, temperature is again a very important factor in food production. Meatexhibits otherparticular quality advantagesasa result of rapidcooling. In meatthepH startsto fall immediately afterslaughter andprotein denaturation begins.The resultof this denaturation is a pink proteinaceous fluid, commonly called ‘drip’, often seenin pre-packaged joints. The rate of denaturation is directly relatedto temperatureandit thereforefollows thatthefasterthechilling rate the lessthe drip. Investigations using pork and beef muscles haveshown that rapid ratesof chill ing canhalve the amount of drip loss. A final, but important, quality and economic advantageof temperature control is a reduction in weight loss, which resultsin a higher yield of saleable material. Meat hasa high watercontent andthe rateof evaporation depends on the vapourpressureat the surface.Vapour pressureincreaseswith temperature and thus any reduction in the surface temperature will reduce the rate of evaporation.The useof very rapidchill ing systemsfor pork carcasseshasbeen shown to reduceweight by at least 1% when comparedwith conventional systems. In a world where consumers require ‘safe food’ of high quality without additives andpreservativesthentemperature is the critical control factor. Most 298 Meat processing of the previous discussion has centredaround chilled foods, but to provide longersafeshelf-lives thancanbe producedby chilling, temperaturecontrol in the form of freezingis againthe answer. 15.2 The impact of chilling and freezing on texture Whilst a number of characteristics affect theoverall quality andacceptability of both fresh and frozen meats, tenderness is the major characteristic of eating quality becauseit determines the easewith which meat can be chewedand swallowed. The tendernessof meat is affectedby both chill ing/freezing and storage. Under the proper conditions, tendernessis well maintainedthroughout the chilled/frozen storage life, but improper chilling/freezing, can produce severetougheningandmeatof pooreatingquality. Refrigerationhastwo critical roles in meattenderness.One is in the prevention of muscleshorteningin the periodimmediatelyfollowing slaughter.The secondis in theconditioning of the meatso that the desired degreeof tendernessis obtained. Chilling hasseriouseffects on the texture of meatif it is carried out rapidly whenthemeatis still in thepre-rigor condition,that is, before themeatpH has fallen below about 6.2 (Bendall, 1972). In this state the muscles contain sufficient amountsof the contractile fuel, adenosinetriphosphate (ATP), for forcible shorteningto setin asthetemperaturefalls below11ºC,themostsevere effect occurring at about3ºC. ‘Cold-shortening’ first becameapparent in New Zealand,when tough lamb beganto be producedroutinely by the improved refrigeration techniques that were introduced after the SecondWorld War (Locker, 1985).As ‘rules of thumb’, cooling to temperaturesnot below10ºCin ten hours for beef and lamb (Offer et al., 1988) and in five hours for pork (Honikel, 1986)canavoid cold-shortening. Thaw shortening, which occurs when a rapidly frozen muscle is thawed, resembles cold-shortening in that it setsin while the level of contractile fuel (ATP) is still high. However, it differs because the amount of work doneand force developed are much higher. With ‘thaw-shortening’ the temperature is raisedthroughthe dangerzonefrom 0 to 10ºC, whereasin cold-shortening it is reducedthroughthiszone.Therateof contraction dependsentirelyon therateof thawing. Rapid thawing of a freely suspended,unloadedmuscle strip causes verydramaticshorteningoftento lessthan40%of the‘frozen’ length. Theterms ‘conditioning’, ‘ageing’, ‘ripening’, ‘maturing’ and‘the resolution of rigor’ have all beenapplied to the practiceof storing meatfor periodsbeyondthe normal time taken for cooling and setting, to improve its tendernessafter cooking. Conditioning imposes a severe limitation on processingconditionsbecauseit is a slow process. The bulk of investigations to determine the time required for tenderising changes to take place in beef have been carried out in North America. DeatherageandHarsham(1947) investigatedthe changes in beefat 0.5 to 2ºC andfoundthat thetendernessof cookedsirloin (Longissimusdorsi) increasedup New developmentsin the chill ing andfreezing of meat 299 to 17 days storagewith some additional improvement up to 31 days. They concludedthatunlessbeefis to beagedbeyondfour weeks,it needonly beaged 2.5 weeks.Doty andPierce(1961)also showedthatconditioning for two weeks at 0.5 to 2ºC improved texture and caused very substantial reductions in the shearstrength of cookedmeat,but much lesschangeoccurred during the next two weeks. Increasingthe delay period before freezing, enhances tenderness becausemeat agesat chill temperaturesbut not at normal freezertemperatures. Meat which has beenconditionedprior to freezing is more tender than that frozen within one or two days and the differenceis maintained throughout frozen storagefor nine months. Freezing rateaffectstherate of tenderisingafter thawing but not theultimate tenderness.Freezing at ÿ10ºC more than doublesthe rate; freezing in liquid nitrogen almosttreblestherate.Freezingis known to causestructuraldamageby ice crystal formation. It seems likely that ice crystals, particularly small intracellular ice crystalsformedby very fast freezingrates,enhance the rate of conditioning probably by releaseof enzymes(Dransfield, 1986). Repeated freeze-thawcyclesusingrelatively low freezing ratesdoesnotseemto causeany enhanced tenderising(Locker andDaines,1973). 15.3 The impact of chilling and freezing on colour Theappearanceof meatat its point of sale is themostimportantquality attribute governing itspurchase.The ratio of fat to leanandtheamountof marbledfat are importantappearancefactors andanotheris thecolour of themeat.The changes in colour of the muscle and blood pigments (myoglobin and haemoglobin, respectively) determine the attractivenessof fresh red meat, which in turn influences the consumers’ acceptance of meat products (Pearson, 1994). Consumersprefer bright-red freshmeats, brownor grey-colouredcookedmeats and pink cured meats(Cornforth, 1994). Red colour is more stableat lower temperaturesbecause the rate of oxidation of the pigment decreases. At low temperatures, the solubility of oxygen is greater and oxygen consuming reactions are sloweddown. There is a greater penetration of oxygen into the meat andthe meat is redderthanat high temperatures. Changes in colour have been reported resulting from chilling treatment. Taylor et al., (1995) found that electricalstimulation of pork producedhigher lightness(L), i.e., paler, valuesthan those measuredin nonstimulated sides. Spray chill ing of pork hassomeeffect on its colour during the initial chilling period (Feldhusen et al., 1995a). After four hours of chilling themusculatureof sprayed ham becomes lighter and red and yellow values decrease.However, after 20 hours there was no significant differencein the colour values.The surfaceof the skin becomeslighter after spraychilling. Newly cut conditionedmeat is known to showa brightersurfaceaftera short exposure to air than unconditioned meat(Doty and Pierce,1961;Tuma et al., 1962;1963).MacDougall (1972)studiedthe effects of conditioning on colour 300 Meat processing andon subsequent storagein packagesof high oxygenpermeability typical of thoseusedfor display and in vacuumpackages of low oxygen permeability. Meat, when cut and exposedto air, changed from dull purple red to a bright cherry red, which is measuredas an increase in ‘lightness’, a ‘hue’ change towards red and an increase in ‘saturation’. The magnitude of the changeon blooming for conditioning meatascomparedwith unagedwasthesame size for ‘ li ghtness’ but was twofold greater for ‘hue’ and threefold greater for ‘saturation’. Conditioned meat,when freshly cut, was lighter but more purple thanthe unconditioned.After onehour exposure to air, conditionedmeathada redder ‘hue’ which was considerably more saturatedand intense than the unconditionedsamples.Thesechanges in lightness,hueandsaturation produced by conditioning result in a brighter, more attractive appearance. The overall colour improvement was of a similar magnitudeto that which occurred on blooming. The colour of frozen meat varies with the rate of freezing.Taylor (1930, 1931)reported that, asthe speedof freezingdiminished, the appearance of the product changed and at very low rates there is a marked development of translucence.Laterexperimentshavedemonstratedadirectrelationshipbetween freezing rate and musclelightness;the faster the rate the lighter the product. Guenther andHenrickson(1962)found that 2.5cm thick steaksfrozen atÿ9ºC weredark.Thosefrozenatÿ34 toÿ40ºChadthemostdesirablecolour andthat those frozen at ÿ73 to ÿ87ºC tended to be pale. Jakobssonand Bengtsson (1969, 1973) obtained similar results; very rapid freezing in liquid nitrogen spray at a freezing rate of about 13 cm hrÿ1 produced meat which was unnaturally pale.Ai r blastfreezing at 2 cm hrÿ1 gavethebestfrozenappearance while very slow freezingat 0.04 cm hrÿ1 resultedin a darker colour and the formation of ice on the product surface. Zaritzky et al. (1983)reported that the surfaceof liver frozenat high rateswas lighter in colour. Thesedifferences in frozen meat lightnessresult from the dependenceof ice crystal growth on the freezingrate.Smallcrystalsformedby fastfreezingscattermorelight thanlarge crystalsformedby slow freezingandhencefast frozenmeatis opaqueandpale and slow frozen meat is translucent and dark. ‘Freezer burn’ is the main appearanceproblemthat traditionally affectedtheappearance of meatin frozen storage. Desiccation from thesurfacetissuesproducesa dry, spongylayer that is unattractive and does not recover after thawing. This is commonly

called ‘freezer-burn’. It occurs in unwrapped or poorly wrappedmeat.The problem is accentuated in areas exposed to low humidity air at high velocities,andby poor temperature control. In thawedmeat therateof pigmentoxidation is increased(Cutting,1970) and therefore the colour will be less stable than in fresh. On prolongedfrozen storage, a dark brown layer of metmyoglobin may form 1–2mm beneaththe surfaceso that on thawing the surface colour will rapidly deteriorate. Meat, which haslost its attractivenessduring frozen storagebecauseof oxidation of oxymyoglobin on the surface, will remain brown after thawing. Unwrapped meatthawedin high humidity air, wateror in steamundervacuumappears very New developmentsin the chill ing andfreezing of meat 301 white andmilky after thawing. However, if thenstoredin a chill roomfor 10 to 24 hoursit will be almostindistinguishablefrom fresh meat.Unwrappedmeat thawedin air at high temperaturesandlow humidities will takeon a dark,dry, tired appearance. It will not recoverits appearance during chilled storageand will often requireextensive trimming before sale. 15.4 The impact of chilling and freezing on drip lossand evaporative weight loss 15.4.1 Drip loss The quality of fresh meat exposedfor retail sale is initial ly judged on its appearance. The presenceof exudate or ‘drip’ , which accumulates in the container of prepackaged meat or in trays or dishes of unwrapped meat, substantially reduces its salesappeal(Malton and James,1983). Drip can be referredto by a numberof different namesincluding ‘purge loss’, ‘press loss’ and ‘thaw loss’ depending on the method of measurement and when it is measured. In general,beef tends to lose proportionately more drip than pork or lamb. Sincemostof theexudatecomesfrom thecutendsof musclefibres,smallpieces of meatdrip morethanlargeintact carcasses.The proteinconcentrationof drip is about140mg/ml,about70%of thatof meatitself. Theproteinsin drip arethe intracellular, solubleproteinsof the musclecells. The red colour is due to the protein myoglobin, the main pigmentof meat. The problem of drip lossis not, however, confinedto retail packs. The meat industry useslarge bonelessprimal cuts,which arepacked in plastic bags,for distribution throughout the trade.Thesemay be storedunderrefrigeration for many weeksbefore useandduring this time a considerablevolumeof drip may accumulate in the bag.Not only doesthis exudatelook unattractive but it also representsanappreciableweight lossto theuserwhenthemeatis subsequently removed from its container. Excessive drip could have a small effect on the eating quality of meat. Perceived juicinessis one of theimportantsensory attributesof meat. Drynessis associated with a decreasein the other palatability attributes,especially with lack of flavour and increasedtoughness(Pearson, 1994). However, moisture lossesduringcookingaretypically anorderof magnitudehigherthanmost drip losses during refrigeration. Consequently, small differencesin drip loss will havelittle effecton eating quality.Thepotential for drip lossis inherent in fresh meat and is influencedby many factors. Thesemay include breed, diet and physiological history, all of which affect thecondition of theanimalbeforeit is slaughtered. Af ter slaughter, factors such as the rate of chill ing, storage temperatures,freezingandthawingcanall influencethe drip produced. Rapid cooling of meatimmediately afterslaughter will reducedrip lossafter subsequentcutting operations.The potential for drip loss is establishedin the first periodof cooling, thetemperature rangeconducive to drip is downto about 302 Meat processing 30ºCor perhapsa little lower. Therearea numberof publicationsshowing that rapid cooling canreduce drip production.Taylor (1972)compared two cooling treatments for pig carcasses.In 38 out of 40 pairedlegs, the drip losswasless after thequickercooling. Thedifferencevariedbetween breed andrangedfrom approximately 1.6–2fold. Gigiel et al. (1985) removedcylindrical samples of muscle from freshly slaughtered beef. The curved surface and one end of the cylinder were surrounded by insulation and the free end placedin contact with solid CO2. Since heat was extractedfrom only one end this produceda wide rangeof cooling ratesthroughthe lengthof the cylinder. Af ter cooling andequalisation, thecylinderwascut into discsandthedrip potentialof eachdiscmeasuredusing a centrifuge technique described by Taylor (1982). Close to the surface in contactwith the CO2 the rateof cooling washighestbut freezing occurred and the drip was high. Minimum drip potential was measured in the next region wherehigh cooling rateswere achievedwithout freezing.Drip thenincreasedas cooling time to 7ºC increased. In meat drip loss increaseswith length and temperature of chilled storage. Work by Lee et al. (1985) clearly showedthe effectof both.Drip lossfrom pork cubesincreasedsubstantially during21 days of storage at 0, 3 and 7ºC. The rate of increasewas greaterat the higher temperatures.In storageat 0 and 3ºC no increase in drip loss with time was measuredafter21days.At 7ºCdrip wasstill increasing between 21and28days. A numberof scientific investigations,which canbe comparedto commercial practice,havedefinedtheeffect of freezingrate on drip production. Petrovic et al. (1993) statedthat the optimal conditions for freezing portioned meat are thosethat achievefreezingratesbetween2 and5 cmhÿ1 to ÿ7ºC.Grujic et al. (1993) suggest even tighter limits 3.33 to 3.95 cm hÿ1. These results are scientifically very interesting, however, in industrial practice most meat is air frozen in the form of large individual piecesor cartonsof smaller portions. In commercial situations,freezingratesof 0.5cmhÿ1 in thedeeper sectionswould be considered ‘fast’ andtherewould be considerablevariation in freezingtime within the meat. The samples frozenby Sackset al. (1993)weremuchsmaller (77.6g in weight) than most commercial products. Even with such small samples there was no significant difference in drip after 48 hours between cryogenic freezingatÿ90ºCanda walk-in freezeroperating atÿ21ºC. 15.4.2 Evaporative weight loss From the momentan animal is slaughtered the meatproduced begins to lose weight by evaporation.Under typical commercial distribution conditions, it has beenestimatedthat lamb andbeeflosefrom 5.5 to 7% by evaporation between slaughter andretail sale(Malton, 1984).Weight lossesfrom pork areprobably of the samemagnitude. In addition to the direct lossin saleablemeatthereare alsosecondarylosses.Excessiveevaporation during initial chill ing andchilled storageproducesa dark unattractive surfaceon the meat.Either this hasto be removedby trimming, or the meatis downgradedandsold at a reducedprice. New developmentsin the chill ing andfreezing of meat 303 Freezing doesnot stopweight loss.Af ter meatis frozen,sublimation of ice from thesurfaceoccurs. If thedegree of sublimation is excessive, thesurfaceof the meatbecomesdry andspongy,a phenomenoncalled ‘freezer burn’. In the United Statesweightlossresultingfrom acombinationof directevaporativeloss and freezer burn in pork bellies stored for one month before curing, was estimatedto be 500000kg (AshbyandJames,1974).Sincethendevelopments in the use of moisture impervious packaging materials have significantly reduced sublimation in frozenmeat. 15.5 The cold chain Thecold chain links temperaturechangingoperations,suchaschilling, freezing, thawing, handling and cooking,and temperaturemaintenanceoperations,such as chilled and frozen storage,transportation and display. In general, as meat moves along the cold chain it becomesincreasingly diffi cult to control and maintain its temperature.Temperaturesof bulk packsof meatandmeatproducts in large storerooms are far less sensitive to small heat inputs than single consumer packsin transport or opendisplaycases. 15.5.1 Primary chilling/free zing Af ter slaughter meat carcassesare at a temperature which is close to the optimum growth temperature for manymicroorganismsandchilling is required before themeatcanbeprocessedor distributed.Thefirst stagein thecold chain will thereforebe a cooling operationto reducethe temperatureof the meatto a value that limi ts microbiological and quality changes.If the meat is to be distributed in a chilled form then this value will be abovethe initial freezing point andin therangeÿ1 to +15ºC. In manycountriesthe legal limit is +7ºC.If a frozen food is required then the value will typically be betweenÿ12 and ÿ30ºC. 15.5.2 Secondary processing Any meat that is processedafter its initial primarychill ing or freezingoperation is likely to gain heatandconsequently rise in temperature. This rise canrange from a few degreesin a packing operation to 100s in cooking. To maintain product quality it is often important to remove this added heat. Industrial cooking processescannotbe guaranteedto eliminate all pathogenicorganisms andif cooling ratesareslow microbial spores that survivethe cookingprocess will germinate and grow. Systems that produce a rapid reduction in the temperatureof the meatwill retardmicrobial growth andconsequently extend shelf life. This is especially important when chilling cookedproducts that will eventually be consumedcold or in a warm reheatedstate. 304 Meat processing 15.5.3 Storage and transport After thetemperatureof themeathasbeenreducedto a desiredvalueit is likely to remainat thattemperaturefor aperiodwhich mayrangefrom a few hours, for chilled products, to a number of years in the caseof frozen foods.During that period it may remain in a single store or be transported around the world. Theoretically, thereshould befew problemsin thestorageandtransport of either chilled or frozenfoods.If themeat is at thecorrecttemperaturewhenit is loaded into thestorageroomor transport vehicle thenall therefrigeration is requiredto do is to insulatethemeatfrom sourcesof heat.Most of thetime themainsource will be a slow movement of heatfrom the outside ambient through the walls, which canbeeasilycateredfor. Copingwith dooropeningsandpeoplemoving around inside the refrigerated chamber is more diffi cult. However, if the standard of management is good, and the meatbulk stacked, then temperature rise in the meatwill be small andrestricted to exposedsurfaces. In practicetherearemanyproblems in meat storageandtransport becausethe meatandmeatproducts arenot at thecorrecttemperaturewhen theyareloaded. If thetemperatureof themeatis too high whenit is wrappedandbulk packaged then it becomesvery difficul t to reducethat temperaturewithin the storageor transport compartment.Sincethesesystemsarenot designedto extractheatthen the averageroom temperature can rise together with that of any other foods alreadystored.Failureto removetherequired heatbeforeloadingcanbedueto a number of causes including, (i) insufficient time allowed, (ii) insufficient refrigeration capacity to cater for high initial product load, (iii) overloading, (iv) variability in sizeof productsor (v) incorrectenvironmental conditions. 15.5.4 Retail display Chilled meatproductsspendperiodsrangingfrom a few minutesto a week in retail displayandin extremecases with frozenproducts a few months.During thattime thereis aconflict between theneedto protectthefood from extraneous heatsourcesandthoseto displayit to its bestadvantage.Retail display cabinets canhaveintegral or remoterefrigerationunits,air movement canbe gravity or forcedair andthe displays canbe single-tier, multi-tier or well. 15.5.5 Domestic transport and storage Even if food producersand retailers maintain acceptable product temperatures duringthedistribution chain they

losecontrolwhentheproductleavestheretail store.After themeat is removedfrom adisplay cabinetit spendsaperiodoutside a refrigerated environment whilst it is carried around the store and then transported home.Temperaturesof foods,especially thin sliced products, can rise considerablyduring these journeys. Consumershaveconsiderablefaith in thetemperaturemaintenanceproperties of domestic refrigerators.However, measurements taken at five positions at fiveminute intervals over an averageof six daysin refrigeratorsin 250 homes New developmentsin the chill ing andfreezing of meat 305 haverevealed considerablevariationin performance.Thehighest recordedmean temperaturewas 11.37ºCand the lowestÿ0.89ºC,producing a rangein mean temperaturesof 12.3ºC.Theoverall meanair temperaturefor all therefrigerators in the survey was 6.04ºC. Consequently, over half operated at mean temperaturesthat would supportthe growth of salmonella. 15.6 Temperature monitoring It is oftenstatedby thosein themeatandrefrigerationindustriesthat ‘anyonecan measurea temperature’.Many millions of measurementsaremadeof both meat andenvironmentaltemperaturesin themeatindustry.However,in manycasesthe measurements made are an unreliable guide to the effectiveness of the refrigeration process.Even when the correct temperatureshave beenobtained the dataareoften poorly analysedandrarely actedupon.The industryneedsto measuretemperaturesaccurately,reliably, meaningfully,simply and cheaply.It needsto beableto analysethedataandrespondwhenrequired.It needsthecorrect instrumentationandthe expertiseto collect andinterpretthe temperaturedata. The first considerationis the rangeof temperatures to be measured.For the meat industry,a rangefrom ÿ40 to +150ºCwould copewith the temperatures foundin freezers,chillers,storagerooms,retail displaycabinets,andin waterused for cleaningor scaldingtanksin theabattoir.If theyproducecookedmeatproducts then the uppertemperaturemay rise to 250 to 300ºC.As well as the measuring rangethe rangeof ambienttemperaturesover which the instrumentwill work needs to be considered.The electronics of many temperature measurement instrumentsare designedto work to the specifiedaccuracyonly within certain ambienttemperatureranges,usually0 to 40ºC.If temperaturesin a cold storeare to be measuredthe instrumentitself may needto be kept warm until it is used. Any temperaturemeasuringsystemshouldbetestedovertheoperatingrange at regularintervalsto ensureaccuracyandshouldalsohavea currentcalibration certificatefrom its manufactureror official standardslaboratory.Thesystemcan be checked by means of a calibration instrument, or against a reference thermometer that is known to be accurate.Melting ice (which if madefrom distilled water shouldread0ºC or ÿ0.06ºCif madefrom tap waterwith 0.1% salt) may be usedto checksensor accuracy. The ice should be broken up into small piecesand placed in a wide-necked vacuumflask with a depth of more than50mm. Thesystemshouldbeagitatedfrequentlyandthe temperature read aftera few minuteswhen stable. If differences of morethan0.5ºCarefoundthe instrumentshouldeitherbe very carefully adjusted, or sentfor calibration. Accuratelydetermining the temperatureof chilled meat throughoutthe cold chain is diffi cult. Training and experience are requiredto locate positions of maximum and minimum temperature in abattoirs, stores,vehiclesand display cabinets.The problemis further exaggeratedby changes in positionwith time caused by loading patternsandthecycling of therefrigeration plants. Obtaining a relationship between environmental temperatures (that can be measured 306 Meat processing relatively easily) and internal meat temperatures is not a simple process. Relating temperaturesobtained in a nondestructivemanner with internal meat temperaturesagainposesproblems.Determining thetemperatureof cutsof meat with regular shapesis quite simple but doing so for irregular cuts of meat is moredifficul t. All thetemperaturemeasurementproblemsassociatedwith chilled foodswill equally apply to quick-frozen foods. In addition, there are a number of other problems. Many instruments have sensors that will accurately measure temperatures of ÿ20ºC and below, but the instruments themselves become inaccurate or fail to operateat low temperatures.If frozen foods are removed from their low temperature environment to one suitablefor the instrument the surfacetemperature risesvery rapidly. However, the main problem is that of actually insertinga temperature sensor into frozen meat. The surfacetemperature of a food or pack can be measured by placing a temperature sensor (suchasthosediscussedabove)in contactwith the surface. In practice therearevery largetemperaturegradientsonbothsidesof thesurface and the presenceof the sensor can influence the temperaturebeing measured. Extending the surfaceof the sensor to measurethe averagetemperatureover a largersurfaceareais onemethodusedto minimisethese problems.This method is recommended for suchapplicationsasbetween-pack measurement. Since it is impossibleto measure the temperature of an exposed surface accurately, the next best thing is to take a measurement of the temperature between two food items.As long asgoodthermalcontactis achievedbetween thetemperaturesensorandthepacks,a between-packmethodshould providean accuratemeasurementof thepacktemperature.If thethermal conductivity of the packaging material is high andthe food makesa goodthermal contactwith the packthenthe temperaturemeasuredwill beclose to that of theproduct. With a product such as skin-wrapped chilled sausages,the above requirements are satisfied. A temperature sensor, especiall y a flatheaded probe, can be sandwichedbetween two packs. An accuratemeasurementis obtained due to the combination of a flexible food and a thin wrapping. With chilled food in cartonsor bubblepacksthe accuracyis much lower. The contact problems are much greaterwith a frozen product. Since the surfaceof a frozen product is not flexible only point contact can be achieved between the surfaceof the product and that of the pack or probe. Using a flat probewith extendedcontactsurfacesdoesnot necessarilyimprove theaccuracy of temperature measurement. In extreme cases, for example with frozen sausages,thecontactsurfacesmayextendout into theair streamandmeasureair not product temperature. With packsof small items such as diced meat the accuracywill be much better.Caremust also be taken to pre-cool the probe before temperaturesare measured.This is especially important with low heat capacitypackaging materials. Noncontacttemperaturemeasurementdevicesmeasure theamountof energy in an areaof the infra-red spectrum that is radiated from the surface being measured. Basic instrumentsmeasurethe averagetemperature of the areain a New developmentsin the chill ing andfreezing of meat 307 small field of view. More complicated systemsof thermal imaging provide a temperaturepicture of all theobjectsovera muchwider area.A certainamount of knowledge is needed in order to interpret the valuesthat such instruments give (Evanset al., 1994;JamesandEvans,1994).Thefirst point to bearin mind when using infra-red thermometry is that the temperature measured is the surfacetemperature.If themeathasbeenin surroundingsthathavenot changed in temperature for a long period of time, then it is likely that the surface temperaturewill be very closeto thatof themeatbeneaththesurface. However, if the temperatureof the surroundingsis changingor haschanged over the past 24 hours,thenit is likely thatthesurfacetemperaturewill not bethesameasthe temperaturedeepwithin the meat.It is alsonecessaryfor the operatorto know how muchof thesurfaceis ‘seen’by theinfra-redinstrument,asit will measure the ‘average’ temperatureover the whole of this area.The targetareacanvary significantly from instrument to instrument and with the distancebetween the instrumentandthe surface. Thereis a furthercomplication in theuseof infra-redthermometers; reflected radiation. The instrumentswill seetheradiationemittedfrom a surfaceandalso an amount of radiationfrom the surroundingsthat is reflectedby that surface. The reflectedradiationwill therefore constitute an error.For warm objectsat a temperaturegreaterthan their surroundings, the amountof reflected radiation will besmall in relation to that from thesurfaceandconsequently theerror will besmall. With frozenmeat,the temperatureof themeat is no warmer than,and oftencolderthan,thetemperatureof thesurroundings.Therefore, theamount of reflectedradiationcoming from the surfaceconstitutesa significant error. Determining the temperatureof small cutsof meatwith regular shapesis quite simple. Determining the temperatureof irregular cuts of meat, and particularly largepieces, is moredifficult. Possibly the mostdifficult problemis ascertaining deep legtemperaturein beefcarcasses.TheMeatResearchCorporationin Australia (1995) recommendthat the temperaturesensorshouldtouchtheTrochanterMajor (aitchbone), which is the‘knob’ of boneontheoppositesideof thefemurto thehip joint. To locate thesensor in this positionit should beinsertedthroughthe ‘Pope’s Eye’ at an angleabout 15 to 20º below the horizontal. It shouldbe aimedat an imaginary vertical line approximately one-third of the distance from the Achilles Tendon to the last tailbone. Becauseconductionoccurs along the steelshaftof a probeit is importantthat theprobeis insertedasfar aspossible into themeat. For example, to takethe temperatureof a cut of meatit is better practice to insert the probeto its full depth alongthelongaxisof thecut rather thanto insert theprobeto half its lengththrough the short axis (CSIRO, 1991). 15.7 Optimising the designand operation of meat refri geration In specifying refrigeration equipment the function of the equipment must be absolutely clear.Refrigeration equipmentis alwaysusedto control temperature. 308 Meat processing Either the meat passingthrough the process is to be maintained at its initial temperature, e.g., as in a refrigerated store or a packing operation, or the temperature of the meat is to be reduced, e.g., in a blast freezer.Thesetwo functions require very different equipment. If a room is to serve several functionstheneachfunction mustbeclearly identified.Theoptimum conditions needed for that function mustbeevaluatedanda clearcompromisebetweenthe conflicting usesmade.Theresult will inevitablybea roomthatdoesnotperform any function completely effectively. There are three stages in obtaining a refrigeration plant. Thefirst is determining theprocessspecification, thesecond is drawing up the engineering specification, i.e. turning processing conditions into terms which a refrigeration engineercan understand,independentof the food processand finally the procurement, the third and final stage being procurementof the plant. Poordesign in existing chillers/freezers is dueto a mismatch between what theroomwasoriginally designedto do andhow it is actuallyused.The first task in designingsuchplantis thereforethepreparation of aclearspecification by the userof how theroomwill beused.In preparing this specification theuserwould do well to consultwith all partiesconcerned; these may be officials enforcing legislation, customers,other departmentswithin the company and engineering consultants or contractors– but the ultimate

decisionstaken in forming this specification are the user’salone. Theaim of drawing up anengineeringspecification is to turn the processing conditionsinto a specification thatanyrefrigeration engineercanthenconstruct anddeliver without knowledgeof the meatprocessinvolved. If the first part of the processspecification hasbeencompleted thenthe engineering specification will be largely in place.It consists of: the environmental conditionswithin the refrigeratedenclosure,air temperature,air velocity andhumidity; theway theair will move within the refrigerated enclosure; the size of the equipment; the refrigeration load profile; the ambient design conditions and the defrost requirements. The final phase of the engineering specification should be drawing up a schedule for testingtheengineeringspecification prior to handing over the equipment.This test will be in engineering andnot productterms. The engineeringspecification shouldbe sentout to tender. If tendershave been selectedfor the quality of their equipment and all accept the tender conditions and say they can meetthe designand test conditions specified, the lowesttender would normally bechosen. Thecontractoris normally responsible for the detailedengineeringdesign,construction and commissioning and the only needis to checkthat this work is carried out in a professionalway. His first responsibility is in carryingout theacceptancetests. Thesetesttheperformance of the refrigeration equipment in termsof the engineering specification andthe plant should not be accepted until satisfactory testshavebeencarried out. The plant can then be handedover and training given to the plant operators in the correct use of the refrigeration equipment. The plant then needs to be commissioned by the factory personnel, systematically increasingthroughput until the processtests canbe carriedout. Theseensurethat the original process New developmentsin the chill ing andfreezing of meat 309 specification in fact achievesthe intended results in terms of temperatures, throughputsandyield. 15.8 Sourcesof further information and advice Food Refrigeration and Process Engineering Research Centre, University of Bristol, Churchill Building, Langford, North Somerset, BS40 5DU, UK. http://www.frperc.bris.ac.uk International Institute of Refrigeration, 177 Boulevard Malesherbes, 75017 Paris, France, www.iifiir.org Processing and Preservation Technology, AgResearch Food Systems and Technology, PrivateBag 3123,Hamilton, New Zealand. 15.9 References ASHBY, B. J. andJAMES,G. N. (1974)Effects of freezingandpackaging methods on shrinkage andfreezerburnon pork belliesin frozenstorage. Journal of Food Science.Vol. 39, pp. 1136–1139. BENDALL, J. R. (1972) The influence of rate of chilling on the developmentof rigor and ‘cold shortening’. In Meat Chilling: Why and How? Meat Research InstituteSymposium No. 2 (ed. C. L. Cutting). 3.1– 3.6. CORNFORTH, D. (1994)Colour– its basisandimportance. Chapter2, pp. 34–78. In Quality Attributesand Their Measurement in Meat, Poultry and Fish Products (eds. A. M. Pearson and T. R. Dutson). Advances in Meat Research Series,Volume 9, Blackie Academic & Professional, UK. CSIRO(1991)Thermometers.MeatResearch NewsLetter. 91/2.CSIRODivision of Food Processing,Meat ResearchLaboratory. CUTTING, C. L. (1970)The influenceof freezingpractice on the quality of meat andfish. Proceedingsof the Institute of Refrigeration. Vol. 66, p. 51. DEATHERAGE, F. E. and HARSHEM, A. (1947) Relation of tenderness of beef to ageingtime at 33–35ºF.Food Research. Vol. 12, p. 164. DOTY, D. M. and PIERCE,J. C. (1961) Beef muscle characteristics as related to carcassgrade,carcassweight and degree of ageing. Technical Bulletin 1231, (Agricultural Marketing Service, United States Department of Agriculture). DRANSFIELD, E. (1986) Conditioning of meat. Recent advances and developments in the refrigeration of meat chill ing, Meeting of IIR CommissionC2, Bristol (UK). Section 1, pp. 61–68. EVANS J. A., RUSSELLS. L. andJAMESS. J. (1994)An evaluation of infrarednon- contact thermometers for food use. Developments in food science 36, Elsevier Science,pp. 43–50. 310 Meat processing FELDHUSEN, F., KIRSCHNER, T., KOCH, R., GRESE, W. and WENZEL, S. (1995a) Influence on meat colour of spraychilling the surfaceof pig carcasses. Meat science.Vol. 40, pp. 245–251. FELDHUSEN, F., WARNATZ, A., ERDMANN, R. andWENZEL, S. (1995b) Influenceof storagetime on parametersof colour stability of beef.MeatScience. Vol. 40, pp. 235– 243. GIGIEL, A. J.,SWAIN, M. V. L. andJAMES,S. J. (1985)Effectsof chilling hot boned meatwith solid carbondioxide.Journal of Food Technology. Vol. 20, pp. 615–622. GRUJIC, R., PETROVIC, L., PIKULA, B. and AMIDZIC, L. (1993) Definition of the optimumfreezingrate.1. Investigationsof structure andultrastructureof beefM. Longissimusdorsifrozenat differentrates.MeatScience. Vol. 33, 3, pp. 301–318. GUENTHER, J. J. and HENRICKSON, R. L. (1962) Temperatures, methodsusedin freezingdetermine tenderness,colour of meat. Quick FrozenFoods. Vol. 25, p. 115. HONIKEL, K. O. (1986)Influence of chilling on biochemical changes andquality of pork. Recentadvances and developmentsin the refrigerationof meat chilling, Meeting of IIR CommissionC2, Bristol (UK). Section1, pp. 45– 53. JAKOBSSON, B. andBENGTSSON,N. E. (1969)The influenceof high freezingrates on thequality of frozengroundbeefandsmallcutsof beef.Proceedingsof the 15th European Meetingof Meat ResearchWorkers. p. 482. JAKOBSSON, B. and BENGTSSON,N. E. (1973)Freezingof raw beef: influenceof ageing,freezing rateandcookingmethodon quality andyield. Journalof Food Science. Vol. 38, p. 560. JAMES S. J. and EVANS J. A. (1994) The accuracyof non contact temperature measurement of chilled and frozen food. IChemE Food Engineering Symposium, University of Bath 19–21/9/94. LEE, B. H., SINARD, R. E., LALEYE, L. C. and HOLLEY, R. A. (1985) Effects of temperature and storageduration on the microflora, physiochemical and sensorychanges of vacuum-packaged or nitrogen-packed pork. Meat Science.Vol. 13, pp. 99–112. LOCKER, R. N. (1985) In Advances in Meat Research, (edsPearson,A. M. and Dutson,T. R.) Vol. 1, pp. 1–44.AVI publishingCo., Westport, Conn. LOCKER,R. N. andDAINES, G. J. (1973)Theeffect of repeatedfreezethaw cycles on tendernessandcooking lossin beef. Journal of theScienceof Foodand Agriculture. Vol. 24, pp. 1273–1275. MACDOUGALL, D. B. (1972) The effect of time and storage temperature on consumerquality. In Meat Chilli ng: Why and How? Meat Research InstituteSymposium No. 2 (ed. C. L. Cutting). 8.1–8.11. MALTON, R. (1984)National Cold StorageFederation Handbook, 17–25. MALTON, R. and JAMES, S. J. (1983) Drip loss from wrappedmeat on retail display. Meat Industry, May, pp. 39–41. MEAT RESEARCHCORPORATION (1995) Measurement of temperaturesin fresh New developmentsin the chill ing andfreezing of meat 311 and processedmeats. Meat TechnologyUpdate, 95/1. Australian Meat Technology Meat Research Newsletter. OFFER,G., MEAD, G. andDRANSFIELD, E. (1988)Setting the scene: the effectsof chill ing onmicrobial growthandtheeatingquality of meat.MeatChilling, IFR-BL: SubjectDay. PEARSON,A. M. (1994)Introduction to quality attributesandtheir measurementin meat,poultry andfish products. Chapter 1, pp.1–33.In Quality Attributes and Their Measurement in Meat, Poultry and Fish Products(eds. A. M. Pearson andT. R. Dutson). Advancesin MeatResearch Series,Volume9, Blackie Academic& Professional, UK. PETROVIC, L, GRUJIC, R. and PETROVIC, M. (1993) Definition of the optimal freezing rate– 2 Investigationsof thephysico-chemical propertiesof beef M. longissimusdorsi frozenat different freezing rates.MeatScience. Vol. 33, pp. 319–331. SACKS,B., CASEY, N. H., BOSHOF,E. andVANZYL, H. (1993) Influence of freezing method on thaw drip and protein loss of low-voltage electrically stimulatedand non-stimulatedsheeps muscle. Meat Science. Vol. 34, 2, pp. 235–243. TAYLOR, A. A. (1972)Influence of carcasschilling rateon drip in meat.In Meat Chilling: Why and How? (ed. C. L. Cutting) Meat ResearchInstitute Symposium No. 2, 5.1–5.8. TAYLOR, A. A. (1982)The measurement of drip lossfrom meat.Meat Research Institute Internal Report. TAYLOR, A. A., PERRY,A. M. andWARKUP, C. C. (1995)Improving pork quality by electrical stimulationor pelvic suspensionof carcasses.MeatScience. Vol. 39, pp. 327–337. TAYLOR, H. F. (1930)Solving problems of rapid freezing. Food Industries. Vol. 2, p. 146. TAYLOR, H. F. (1931)Whathappens duringquick freezing.FoodIndustries. Vol. 3, p. 205. TUMA, H. J.,HENRICKSON,R. L., STEPHENS,D. F. andMOORE,R. (1962)Influenceof marbling andanimalageon factors associatedwith beef quality. Journal of Animal Science. Vol. 21, p. 848. TUMA, H. J., HENDRICKSTON, R. L., CEDILLA, G. V. and STEPHENS, D. I. (1963) Variation in the physicaland chemical characteristicsof the eye-muscle from animalsdiffering in age.Journal of Animal Science. Vol. 22, p. 354. ZARITZKY, N. E., AÑON, M. C. andCALVELO, A. (1983)Rate of freezingeffect on the colour of frozenbeef liver. Meat Science. Vol. 7, pp. 299–312. 312 Meat processing 16.1 Introduction: high pressure treatment and meat quality High pressure technology, defined as a pressure treatment between 100 and 1000 MPa, is derived from the ceramic industry. It is of increasing interest to food processing because of its potential to decrease the level of microbial contamination without any heat treatment. Industrial high pressure food products are mainly manufactured in: • Japan (fruit jams and juices, sake, ham, fish and rice products) • the USA (oysters and fruit juices) • Mexico (fruit juices) • Spain (ham and other meat products) Research on the effect of high pressure on food began one hundred years ago (Hite, 1899) but only expanded significantly in the 1990s. High pressure processing of meat has been an active topic of research because of its potential to extend shelf-life (Ledward, 2002). However, pressure treatment brings about changes in the constituent molecules of meat, and could affect functional properties of meat such as colour and gelation properties. This chapter deals with the effects of high pressure on the constituents and quality attributes of meat products, and with current and potential industrial applications of this technique. Meat and meat products are solid foods so high pressure treatment requires the use of a discontinuous system. The most common technique involves vacuum wrapping and putting meat in a pressurizing vessel. In the presence of the pressure medium (water), the pressure increases at a rate of 100 or 200 MPa/min (Tonello, 2001). When the appropriate pressure level is reached, valves are closed and the pressure remains constant (Fig. 16.1). The 16 High pressure processing of meat M. de Lamballerie-Anton, ENITIAA, Richard G. Taylor and Joseph Culioli, INRA food industry generally uses pressure between200 and 800MPa, with the duration of pressurekept asshortaspossible (about 15 min. max.). 16.2 General effect of high pressureon food components Reactionsof food componentsunderpressureare governed by Le Chatelier’s principle,according to which a processassociated with a decreasein volumeis favored by an increase in pressureandvice versa. Volume changes aredue to molecular conformation modifications, intramolecular

interactions, solvent variation, and chemical reactions. Weak energy bonds such as hydrogen, hydrophobic or ionic bondsare affectedby high pressuretreatment, whereas covalent bondsare not modified. The main effects of high pressure on meat componentsareon water, proteins(including enzymes)andlipids. 16.2.1 Water At 600MPa and 22ºC, water is compressedby 15%. Meat and meat products usually contain significant amountsof waterandtendto compressby a similar amount. Packaging must take this compression into account. Adiabatic compression of water also induces an increase of temperature about2 or 3ºC for each 100MPa (Hayashi, 1991) which can be dissipated by heat transfer between the food andthe pressurizingwater (Cheftel andDumay, 1997).High pressurealsoinducesthereversible dissociationof water, decreasingpH by 0.73 when pressureis increasedfrom 0.1 to 100MPa(Cheftel,1991). This changeis significant because of its potential effect on proteins (seesection 16.2.2). In addition, pressuredecreasesthe melting point of ice below 220MPa, allowing thawing underpressureat subzero temperature. Fig. 16.1 High pressureprocessingvessel(courtesyof ACB PressureSystems,France). 314 Meat processing 16.2.2 Proteins and enzymes The effect of high pressureon proteinsis highly dependent on the structureof the macromolecule and the composition of the medium aroundit (pH, ionic strengthand temperature).Generally the primary structureis not modified by pressure, whereas secondarystructureis only affectedby very high pressure treatment (Mozhaev et al., 1994), and tertiary and quaternarystructures are modified from 100MPa (Galazkaet al., 1996).Thesechanges in structurecan alter theactivity of endogenousmeatenzymes. However, studiesof theeffectof high pressureon enzyme activity are complicated becauseenzymes react differently whenthey havebeenextractedfrom food (Hendrickx et al., 1998). High pressure treatment induces activation or inactivation of enzymes depending on conditionsof buffer andpressure(seesection 16.4). 16.2.3 Carbohydratesand lipids High pressureactsonly on polysaccharides. Glycogenis theonly polysaccharide presentin muscle, but post-mortemmeat generally doesnot containanyresidual glycogenbecauseof the postmortemglycolysis(Lawrie, 1998). Meat products therefore, arenot affectedby pressuremodification of carbohydrates. High pressuretreatment can induce some modification of lipids, but it is difficul t to makegeneralconclusionsaboutlipid changesin meatwith regardsto oxidation andfree fatty acids formationresulting from pressure.High pressure doesincrease themelting point of lipids. At roomtemperature triglyceridescan crystalliseunderpressure,which may alter the structureand,asa consequence, the permeability of cell membranes. This mechanismcould be involved in the inactivation of bacteria. 16.3 Structural changesdue to high pressuretreatment of muscle The effectsof high pressuretreatmenton muscle structurehavebeenexamined for beef (Jung et al., 2000a; Kennick et al., 1980; Locker and Wild 1984; Macfarlaneet al., 1980;Ueno et al., 1999;Suzukiet al., 1992),sheep(Kennick et al., 1980;MacfarlaneandMorton 1978), poultry (Yusteet al., 1998)andfish (Ashie et al., 1997).In addition some of these effectshavebeendiscussedin a previous review of the effects of pressure treatment on meat (Cheftel and Culioli, 1997). Before discussingtheseeffects it is necessary to give a brief review of post-mortemmeat changesat atmospheric pressure. Normal muscle structure has been thoroughly reviewed (Bendall, 1973; Bloom andFawcett,1975;Goll et al., 1984)and,for thepurposeof this chapter, can be simply described as a composite structure composed of myofibers organizedin bundlesby connective tissue.Mostof thestructural changes related to high pressuretreatment of meathaveexamined the ultrastructureof muscle, especially theattachment of sarcomeresto eachotherandto theendomysiumby High pressureprocessing of meat 315 the cytoskeleton (cytoskeletal structurehas been reviewed by Thornell and Price, 1991; Squire, 1997). Interpreting the effects of high pressure is complicatedby inherentvariability in meatstructureandthe rapidpost-mortem changes. Thereareultrastructural differences between musclefiber typeswhich include Z line width and mitochondrialcontent. Thereare also differencesin post-mortemchanges relatedto fiber type (Abbot et al., 1977; Stromer et al., 1967).Normal post-mortem changes include: • fiber-fiber detachmentin fish andmammals (Taylor andKoohmaraie,1998; Taylor et al., 2002;Will et al., 1980) • breaks in I bandsand intermediate filaments (Taylor et al., 1995;Ho et al., 1997) • extensivedisruption of the reticulum(Will et al., 1980) In general structural changes are similar in fowl (MacNaughtan,1978), pork (Abbot et al., 1977), beef (Davey and Gilbert, 1969; Gannand Merkel, 1978; Will et al., 1980)andsheep(Taylor andKoohmaraie,1998).However,fish do not showI bandbreaks (Papaet al., 1997,Taylor et al., 2002),oneof themajor features of other meat animals. Connective tissueof mammals is stablepost- mortem with few structural changes for several weeks (McCormick, 1994; Purslow, 1994). Structural changesdueto pressuretreatmentof meat arevery dependent on time postmortem,temperature,pressureand,to a lesserdegree,onspeciesor on muscle type. If pressuretreatment is applied pre-rigor there is extensive contraction of four different sheepand beef musclesgroups,with 103MPa causing shrinkage of up to 48% (Kennick et al., 1980) and disruption of the sarcolemma.Similar results are reported for sheep(Macfarlane and Morton 1978)andbeef(Boutonet al., 1980,ElgasimandKennick,1982),with pre-rigor treatment causing contraction of fibers, contraction bands and sarcolemma disruption. Detailed structural studiesusing SEM andTEM alsoreveal changes in sarcomeric structurewith lossof M linesandsomegapsin theZ line (Elgasim andKennick, 1982). Treatmentof meat post-rigor doesnot resultin extensive contraction (Junget al., 2000a,MacfarlaneandMorton, 1978,Suzukiet al., 1992)andcanimprove tenderness.In general,at ambient or lower temperaturesandlow pressures,there is little or no structural change, for example at: • 130MPa and10ºCfor beef (Junget al., 2000a) • 100MPa and20ºCfor bluefish(Ashie et al., 1997) • 100MPa and10ºCfor beef (Suzuki et al., 1992;Ueno et al., 1999) At theserespectivetemperatures, increasingthe pressure causes M line loss, disruption of thin filamentorganization, thickening of Z lines(Jungetal., 2000a, Suzuki et al., 1992),some fiber breaksandalsodisruption of endomysiumand perimysium organization (Ashie et al., 1997,Ueno et al., 1999). Theseeffects havebeenproduced, for example, by increasing the pressureto: 316 Meat processing • 325MPa andaboveat 10C for beef (Junget al., 2000a) • 200 or 300MPa for bluefish(Ashie et al., 1997) • 200MPa and10ºCfor beef (Suzuki et al., 1992, Ueno et al., 1999) At 150MPaand0ºCfor 3h thereis lossof M linesandI banddisruption in beef (Macfarlaneet al., 1980),andsimilar changes at 150MPa and20ºCfor 5 min. (Suzuki et al., 1990).Due to the great variability of parametersinvolved, it is difficul t to saythat 150MPa is a critical pressurewhich inducesultrastructural change. The general conclusion is that, at ambient temperatures or less and pressures of lessthan150MPa, thereis little to no structural changein meat. Studies such as these show that I band disruption, M line loss and endomysium/sarcolemma detachment are hallmarks of high pressure-induced structural changes in meat. Other frequently reported fiber-related changes includeincreasedspacebetweenfibers(Elgasim andKennick, 1982,Junget al., 2000a,Yuste et al., 1998). In addition both fibers (Yuste et al., 1998) and sarcomeres (Jung et al., 2000a) have increased diameters after pressure treatment. Suzuki et al., (1991)haveexamined structural changesin pressure- treatedpreparationsof purified beefmyofibersandalsofoundM line loss,Z line thickening andI banddisruptionasreported for wholemeat. However, theyalso observedmoreextensivechanges,notably A bandbreaks,not reportedfor whole meat. Combining pressurewith heat treatment increases effects on structureand alsocauses changesat lower pressures.Treatmentof sheepat 100MPafor 1h at 25ºC, for example, causes M line loss and I banddisorganization (Macfarlane and Morton, 1978). At temperaturescloser to normal cooking temperatures, pressure-inducedstructural changescan be extensive. Locker and Wild found ultrastructural changes in beef treated at 60MPa and 50ºC to 65ºC which included disruptionof thin filament organization, M line loss and increasedN lines in the I bandindicatingprotein aggregation (Locker andWild, 1984).At 60ºC and higher pressuresof 150MPa (Bouton et al., 1977, Macfarlane and MacKenzie, 1986), beef muscle shows thicker Z l ines, thin fi lament disorganization, M line loss and also breaks within the A band.This muscle structureis normally very stablepost-mortemandevenat cooking temperatures (Joneset al., 1977,Leander et al., 1980). Theconnective tissueultrastructurehasalsobeenexamined in high pressure treatedmeat.As mentionedabove,the endomysium detachesnormally in meat andthis is enhancedby pressuretreatment. Undercertain conditionstherecanbe breaksin theendomysium(Uenoet al., 1999,Ashie et al., 1997).Thesechanges tendto beminorandother authorshavereported nochangesin connective tissue structuredueto high pressure(Suzuki et al., 1993,Yusteet al., 1998). Thereis onereportof changes in lysosomal ultrastructure in beef treatedat high pressure. Jung et al., (2000b) examined lysosome ultrastructure in beef storedfor 48 hoursandthentreatedat pressuresfrom 0 to 600MPa for various timesat 10ºC.At pressures above300MPathelysosomeswereswollenandhad disrupted membranes. Under these conditions the content of free lysosomal High pressureprocessing of meat 317 enzymesincreases,andmaycontribute to some of thechangesobserved.These observations are similar to lysosomalchanges after 14 days of meat ageing (Chambers et al., 1994), suggestingthat high pressureaccelerates normal lysosomalchanges. 16.4 Influence on enzymereleaseand activity Enzymatic reactionsare highly susceptible to high pressure treatment, and muscle enzymesareparticularly significant in the tenderizationof meat during ageing. As a result, the effect of high pressureon meat enzymeshas been extensively studied. 16.4.1 Calpain system and proteasome High pressure treatment increasesproteolytic activity of muscular enzymes (Homma et al., 1994). Homma et al. (1995) showed a decreaseof calpain activity in meat whenit waspressurized, andthat barosensibility wasdifferent according to calpain type. Proteasomeactivity is enhanced at 150 MPa, but decreasesat higherpressurevalues(Otsukaet al., 1998). 16.4.2 Lysosomal enzymes High pressure treatment of muscle induces a release of lysosomal enzymes (Homma et al., 1994, Elgasim et al., 1983) due to lysosome membrane breakdown (Jung et al., 2000b).Generally, activity of cathepsinD and acid phosphatase in pressurizedmeatsamplesis higherthanin controlsamplesat two dayspost-mortem andduring storage(Junget al., 2000c). 16.4.3 ATPaseand glycolytic activity Yamamoto et al. (1993)showedthatmyosinATPase activity decreased assoon as 70MPa was applied, and that activity fell to zero after 210MPa. Horgan (1980)showeda decreaseof Ca2+-dependantATPase activity in pre- andpost- rigor meat.But glycolysis mayincrease with pressurebecauseof phosphorylase activation

associatedwith changesof pH andfree Ca2+ (Elkhalifa et al., 1984). 16.5 High pressureeffectson the sensoryand functional propert ies of meat 16.5.1 Texture Resultspresentedin Table16.1 showthat severalgroupshavefound that high pressure can tenderize meat when applied pre-rigor. However, high pressure treatmentdoesnot havetheseeffectsif combinedwith commercialconditions 318 Meat processing for meat ageing,i.e. post-rigorandat low temperature.High pressuretreatment of post-rigor muscle causes a significant increase in lysosomalenzyme activiy, but doesnot improvemeattendernessor reducethe ageingtime. 16.5.2 Color and lipid oxidation Meat color characteristics in the CIELAB system, i.e. L* (lightness), a* (redness) and b* (yellowness)are modified by high pressure processing. L* increases from 250MPa to 350MPa and then becomesconstantfor higher pressurevalues. As a consequence, bovine meat appears lighter and less red (Carlezet al., 1995,Shigehisaet al., 1991).This modification of lightnessis due Table 16.1 Effect of high pressuretreatmenton meattenderness(from Jung,2000d) Time High pressure Cooking Effect on Authors post- treatment conditions tenderness mortem pre-rigor As far as130MPa 90ºC,1h T Macfarlane(1973) post-rigor 30–40ºC,1–8min WE pre-rigor 20 to 140MPa 75 and80ºC, T Boutonet al. (1977) post-rigor 25 to 60ºC,2.5min to 1h 1.5 h WE pre-rigor 103MPa Microwave T Riffero andHolmes 35ºC,2min + grill (80ºC) (1983) pre-rigor 103.5MPa 80ºC,40min T ElgasimandKennick 37ºC,2min (1982) pre-rigor 103MPa 80ºC,40min T Kennick et al. (1980) 35ºC,2min post-rigor Pre-cooking45ºC,45min 80ºC,90min T Boutonet al. (1980) 150MPa 60ºC,30min 80ºC,24h post-rigor 60MPa 80ºC,40min T Locker andWild 25–65ºC,5–20min raw WE (1984) post-rigor 150MPa 80ºC,1h T Beilken et al. 40 to 80ºC,1 to 4h WE (1990) post-rigor Pre-cooking45ºC,45min 80ºC,2h T Ratcliff et al. 150MPa 60ºC,30min (1977) post-rigor Pre-cooking45ºC,45min 80ºC,1h T Robertsonet al. 150MPa 60ºC,30min (1984) post-rigor 150MPa 30 or 60ºC 80ºC,1h WE Macfarlaneand 1.6 or 16h T McKenzie(1986) post-rigor 150MPa 25,50 or WE Macfarlaneet al. 0ºC, 3h 80ºC,1h H (1980) post-rigor 500MPa H Yusteet al. (1998) 2ºC, 10 or 30min post-rigor 400 to 600MPa 80ºC,20min WE Margeyet al. (1997) 20 to 50ºC,15min post-rigor 200 to 350MPa raw T Mussa(1999) 20ºC,5 to 100min post-rigor 520MPa,260s, 10ºC 65ºC,1h H Junget al. (2000c) T: Tenderizing WE: Without Effect H: Hardening. High pressureprocessing of meat 319 both to myoglobin denaturation (Carlez, 1994) and myofibrillar proteins denaturation (Goutefongea et al., 1995). The a* index decreaseswhen meat hasbeenpressurizedat higher pressures (400–500MPa),becauseof theincrease of the metmyoglobin content (Ledward, 1998), while the b* index remains constant (Riffero and Holmes, 1983) and the meat becomes brown. Metmyoglobin formation can be prevented by complete removal of oxygen throughvacuumpackagingwith anoxygenscavenger, or by previousformation of nitrosylmyoglobin, as in processedbrined products (Carlez et al., 1995; Goutefongeaet al., 1995). Although high pressuretreatment inducesvisible modifications of the color of raw meat,after cooking the color differenceis greatly reduced (Junget al., 2000c). Cheah and Ledward (1996) showed that high pressure(800 MPa, 20 min) treated pork mincesamplesrevealedfasteroxidationthancontrol samples, and that pressuretreatment at greater than 300–400MPa causedconversion of reduced myoglobin/oxymyoglobin to the denatured ferric form. Cheah and Ledward (1997) also demonstratedthat iron releasedfrom metal complexes during pressuretreatment catalysedlipid oxidation in meat.Accordingto Orlien and Hansen, (2000), 500MPa is a critical pressure for lipid oxidation and developmentof rancidity in chicken breast muscle. Lipid oxidation at higher pressuresis not relatedto the releaseof non-hemFe or catalytic activity of metmyoglobin, but could be linked to membranedamage. 16.5.3 Gelation and emulsifying properties The meatproductsindustry depends on exploiting the functional properties of myofibril lar proteins, including water binding, gelling and emulsifying properties. High pressuremay induce gelation of myofibrillar proteins without heating (Hermansson et al., 1986). When myofibrillar proteins have been previously submitted to high pressuretreatment, heated gels are stronger (Ikeuchi et al., 1992a). Thesemodificationsaremainly linked to the increase of hydrophobicity and sulfhydryl interactionsof myofibrillar proteins (Ikeuchi et al., 1992b,Chapleauet al., 2002). CrehanandTroy (2000)haveshown that the emulsion stability of meatwas increased in frankfurters made with 1.5% NaCl after exposure of the meat to 150MPa.Generally speaking, high pressureimprovesmeatbinding properties, partially compensating for a reductionof the NaCl content of meatproducts. 16.6 Pressureassistedfreezing and thawing As Fig. 16.2shows, the phasechangetemperature of waterdecreasesfrom 0ºC down to ÿ22ºCwhenpressureincreasesup to 220MPa.The oppositeeffect is observed abovethis pressure.This phenomenon can be usedto achieverapid thawing or freezingof foods, suchasmeat, which containa significant amount of water.Slow freezing results in largerice crystals,which generallydamagethe 320 Meat processing texture of the food, whereasa rapid freezing rateusually preserves food texture (Sanzet al., 1999). Rapid freezing using high pressurecan be achievedby cooling atÿ20ºCand200MPa. In theseconditions waterremainsin the liquid state.Upon release of pressure, instantaneous and homogeneous crystalisation occurswith formation of very small crystals. This methodhasbeenshownto preservethe textural properties of pork meat as well as traditional methods (Martino et al., 1998). High pressurethawing also offers several advantages in comparison to thawingat atmosphericpressure,including thereduction of the thawingtime by 2 to 5-fold in comparisonwith conventional processes,andpartialdestructionor growth limit ation of pathogens(Haackand Heinz, 2001). Zhao et al., (1998) haveshown that high pressurethawing maintainsthe organoleptic properties of bovinemeat. Additional studiesarenecessary to betterunderstandwaterholding capacityand protein denaturation during high pressurethawing (Knorr et al., 1998). 16.7 Effects on microflora Theuseof highpressurefor foodpreservation wasproposedmorethanacentury ago.Firstapplied to milk (Hite, 1899),high pressurewasthenusedto treatfruits and vegetables(Hite et al., 1914),and other food products suchas meat.The resistance of bacteria,enzymesand toxins to pressuretreatments has been investigated for many years sincethe pioneering work published by Larsonet al., (1918) and Bassetand Macheboeuf (1932). However, the first industrial Fig. 16.2 Phasediagramof waterunderpressure(from Kalichevskyet al., 1995). High pressureprocessing of meat 321 application of high pressurepreservation was not developeduntil the 1990s when largescaleequipmentweredevelopedfor continuous treatment of liquids suchasfruit juice. High pressureprocessingeffectively inactivatesspoilagemicro-organismsas well as food borne pathogens (Cheftel, 1995). This inactivation is due to widespread damagesof microorganisms through modification of morphology and of severalvulnerable componentssuchascell membranes, ribosomesand enzymes,including thoseinvolved in the replication andtranscription of DNA (Yuste et al., 2001a). The effect of high pressureon bacterial survival is influencedby a number of interacting factors suchasmagnitudeanddurationof the treatment, temperature, environmental conditions, bacteria species and developmentphase(Pattersonet al., 1995). At ambienttemperaturevegetative cellsareinactivatedbetween400 and600 MPa. In general, gram-positive bacteria (Listeria monocytogenes, Staphy- lococcus aureus) are more resistantto pressurethan gram-negative(Pseudo- monas, Salmonella spp, Yersinia enterocolitica, Vibrio parahaemolyticus), but largedifferences canexist betweenstrainswithin the same species. Moreover, cocci are more resistantthan rods because of fewer morphological changes underpressure.In addition,culturesin the exponential growth phasehavebeen shown to be far more sensitive than cultures in the logarithmic growth or stationaryphase(Hooveretal., 1989).In contrast,sporesatambient temperature canresistpressures up to 1000MPa, temperaturesabove70ºCbeingnecessary to obtain asignificantlevel of inactivation. However, it hasalso beenshown that lower pressures (250MPa) associated with mild temperatures (40ºC) can inactivatespores in a two stageprocess,pressurefirst inducing germinationand then inactivating the baro-sensitive germinated spores. In addi tion, pressurisation can inactivatesome parasitessuchasTrichinella spiralis but its efficiency on inactivation of virusesis very limit ed (Cheftel, 1995). The applicationof high pressurecan producea populationof stressedcells which can be revived in certain environmental conditions. As a consequence, pressureinactivation of bacteriamaynot beeffective. Attachmentof bacteriato certain food constituents such as protein, carbohydrates, and lipids may also confer a baro-protection which limits theeffectivenessof high pressure.Indeed, pressure resistance of bacteria has been shown to be dependenton culture medium. UHT milk, for example,exhibits a protective effecton Staphylococcus aureus, Listeria monocytogenesand Escherichia coli O157:H7 compared to porkslurryor poultrymeat, whereashighpressureis themost effectivewhen the bacteria are inoculated in pH 7.0 phosphatebuffers (Pattersonet al., 1995). It hasalso beenshownthat theuseof inoculatedflora mayleadto over-estimation of the effectivenessof high pressure.Carlez et al., (1994) noted that minced meat endogenousflora wasmore resistantto pressurethaninoculatedcollection strains. A processcycle at both low and high pressures may be more effective in inactivating vegetative bacteriathancontinuoustreatment (Yusteet al., 2001a). However, the successof this approachdepends on conditionssuchasintensity 322 Meat processing andduration of pressuretogetherwith otherfactors suchastemperature(Yuste et al., 2001b). In general,full sterilization of food products is not possible with high pressureat levelsbelow500MPa.Most industrial applicationsoperate at a ceiling of 400 to 500MPa maximum, and products require chilled storageto maximize shelf-life. The combination of high pressurewith other physical treatments (such asradiation, pulsedelectric fields or ultrasound,for example) or chemical preservation methods (such as bacteriocins, chitosans or antioxidants)hasbeenproposedin orderto enhance its efficiencyand/orreduce the severityof the other treatments (Yusteet al., 2001a). Thefact thatpressure-stressedcellsmaybelessresistantto heatcouldexplain theefficiencyof combinedhigh pressure andmoderatetemperaturetreatmenton bacteriainactivation.High pressureis well adaptedto ‘pasteurization’of animal food productssensitiveto heat.In particular,it canbe appliedto foie grasfrom fatty gooseor duck,increasingits microbialsafetyandshelf-life. Conditionssuch aspressure at 400MPaandtemperaturein the50–60ºCrangeappliedfor 5 to 15 min. have beenshown to be efficient for preservationwithout the lipid loss associatedwith thermalpasteurisation(El Moueffak et al., 1996).High pressure canalsobeusedto increase thesafetyof meatscookedat low temperatureover a long period. This techniqueincreasesthe tendernessof meat as long as the temperatureis keptno higherthan60–65ºCto avoidcontractionof collagenand resultingcookinglosses. Finally,

pressurecanbeusedfor preservationof already packagedmeat products which may have been contaminatedearlier during processing. In particular, packaged sliced ham and salami emulsion-type sausagesare well adaptedto pressuretreatment,in part due to the stability of their pink or red color under pressure(CheftelandCulioli, 1997). 16.8 Current applications and future prospects Stabilization of fruit products(suchas fruit juices, jam and avocado paste)is currently the main field of applicationfor high pressurein the food industry. Japanwasthefirst countryto manufacturepressurizedproductssuchasfruit jam on a commercial scaleduring the1990s.The mainapplicationsof high pressure treatment in the meatindustryarein stabilizingmeat productsandtexturing of meat paste in combination with thermal processing. As an example, high pressuretreated,cookedandslicedhamhasbeenproducedsince 1999in Spain by the Espuña Company and hasextendedproduct shelf life to several weeks (Fig. 16.3).Thesamecompanyhasalsoexpandedtheuseof high pressureto the manufacture of products such as meat ‘tapas’. There remain a number of constraints on development,including cost.Early estimatessuggested that high pressureprocessing could be asmuch astwenty timesthe costof conventional thermal technologies(Manvell, 1996).In addition,moreresearch is requiredto establish process parameters for microbial and enzyme inactivation. Such research is essentialin the context of regulatory approval (for example, in meetingtheEU’s Novel FoodRegulation)permitting a larger-scalecommercial High pressureprocessing of meat 323 breakthrough for this technology (European Community, 1997). 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(1998)Microscopicchangesin poultry breast muscle treated with high hydrostatic pressure.44th ICoMST, 550–551. 330 Meat processing YUSTE J., CAPPELLAS M., PLA R., FUNG D.Y.C. and MOR-MUR M. (2001a). High pressureprocessingfor food safetyand preservation:a review. J. Rapid Methodsand Automation in Microbiology, 9, 1–10. YUSTE J., PLA R., CAPELLAS M., SENDRAE., BELTRAN E. andMOR-MUR M. (2001b). Oscillatory high pressureprocessingapplied to mechanically recovered poultry meatfor bacterialinactivation. J. Food Sci., 66, 482–484. ZHAO Y., FLORESR.A. andOLSOND.G. (1998)High hydrostatic pressureeffectson rapid thawing of frozenbeef.J. Food Sci., 63, 272–275. High pressureprocessing of meat 331 17.1 Introduction A variety of restructured meats have been marketed successfully over the last 30 years in the UK, the USA and elsewhere. The success of these products has arisen from consumer demand for convenience, variety, consistent quality and, also, the economic desirability for the manufacturer to upgrade meat raw materials. Products are referred to, variously, as ‘restructured’, ‘reformed’, ‘flaked and formed’, ‘chopped and shaped’ and ‘chunked and formed’ determined to a large extent by the size of the constituent pieces (Franklin and Cross, 1982; Sheard and Jolley, 1988). The term ‘intermediate value products’ is also used (Breidenstein, 1982), suggesting that this type of product is perceived by the consumer, and marketed, as intermediate in value between traditional burgers and intact muscle steak. In the UK, products are usually frozen, may be breaded and coated, and are usually rib or steak-shaped, with an appropriate coined name (e.g. joysteak, grillsteak or ribsteak). Restructured meats may also be used as an alternative to ordinary diced meat in canned meats or ready meals. Some products are sold in a bun or as the main component in a ready meal. The largest, and most easily identified, sector is that for grillsteaks. A UK survey of grillsteak-type products showed that most have a meat content of 93% or above, though some were as low as 55% (Jolleyet al., 1988). Beef was the main ingredient in the products surveyed, though restructured ribs are usually pork and there are some lamb products. Poultry meat also features strongly. All the products included in the survey contained salt; phosphate, soya and caseinate were common in products with lower meat contents. Meat restructuring ‘involves the assembly of meat pieces into a cohesive product which aims to simulate or retain the texture of high quality muscle’ 17 Processing and quality control of restructured meat P. Sheard, University of Bristol (Sheard andJolley,1988).This definition is useful in that it conveys something of the way in which the products are made: comminution followed by re- assembly or thebinding together of theconstituent pieces.It alsoprescribesthe objectivein termsof the desiredtextureandthe way in which that is achieved: eitherby simulation (which is necessarily the casewherethe meatshavebeen finely comminuted to a pasteor emulsion) or by retaining the typical fibrous texture of good quality whole muscle, as is the casewhere the piece size is relatively large (e.g. chunked and formed products). Cohesion is developed duringcookingby thegelation of meatproteinssolubilisedduringprocessingby the actionof salt. Most of thepublished researchhasemanated from theUnitedStates(seefor example, Franklin and Cross,1982; Pearsonand Dutson, 1987) where there appears to be a greater useof freshmeatthan in the UK and more product is targetedat the food service(catering) sector(Field, 1982), including the armed forces(Shults, 1982).This review,for obviousreasons,focuseson thesituation in the UK wherethe useof semi-frozen meat is more common. Section 17.2 describes the sequence of operations involved in the manufacture of UK-style grillsteaks(tempering,pre-breaking,flaking, mixing, formingandfreezing).The samestages,with a few modifications, are employed in the manufacture of restructured roasts and diced meat. Factors affecting product quality are discussed in Sections 17.3–17.6 which highlight the need for accurate temperature control at the pre-break stageand explains the role of salt and phosphate in producing an adequatebind. Also included is somepreviously unpublished data from this laboratory. Some recent developments are highlightedin Section17.7. 17.2 Product manufacture The manufacture of UK-style grillsteaks involves a series of operations, summarised in Fig. 17.1 anddescribed below. 17.2.1 Raw materials

Most productsare madefrom frozen meat (at ÿ18ºC) and distributedfrozen. Frozen meat is usually purchasedas 27kg blocks specified with respect to animal(e.g.cowor steerandage),cut (forequarter cutssuchaschuckandblade, flank andbrisket,neckandshin) andamountof fat, usually on thebasisof visual lean.Before the crisis surroundingbovine spongiform encephalopathy(BSE) it was common to use cow meat (5–8 years old) for grillsteak production. Arguably (seefor example Crosset al., 1976), the quality of grillsteaksmade post-BSE has improved given the requirement to useanimals of less than 30 months which yields more tender meat than that from older animals. The manufacturer is unlikely to have any control over factors, other than those specified,which might influenceprocessingquality beforethe blocks arrive at Processing andquality control of restructuredmeat 333 the factory. Otherraw materials may includemechanically separatedmeat, salt, phosphate, onion, rusk, spices,monosodium glutamate, hydrolysed vegetable protein, sodiumbisulphite andcasein. 17.2.2 Tempering Meatat18ºCis extremely hardandprocessingat frozentemperaturescanleadto equipment damage(Koberna, 1986). It is usual, therefore, to temper frozen Fig. 17.1 Methodof manufactureof UK-style grillsteaks. 334 Meat processing blocks, i.e., to increase the temperature of the block, usually to a target in the rangeÿ2 toÿ10ºC,to facilitate furtherprocessing. Theredoesnot appearto be anyideal temperatureand,in practice, thetargettemperatureis usuallybasedon pragmatic considerationsandpastpractice (‘we’ve alwaysdoneit like this’). In onecompany,thetargettemperatureis governedby thecapability of theformer at the endof the processingline which operates well only at low temperatures. Increasing meat temperature to the target, reducesthe ice content but, more importantly, modifiesthemechanicalpropertiesof theblock (seeSection 17.3). Two methodsof tempering areused:cold roomor microwave, or sometimes a two-stage temper(microwave followed by cold room tempering), the latter giving bettercontrol over temperature.The main disadvantagewith cold room tempering is thatseveral daysarerequired to reachthetargettemperaturewhich, in turn, requiresproduction to be forecast several daysin advance. Cold room tempering often gives rise to temperature variation within (the surfacebeing warmer thanthe interior) andbetween blocks(JamesandCrow, 1986).Therate at which meat tempersdepends on the way in which blocks are stacked,air speed, temperature and position within the cold room. Poor stacking can markedly extendtempering times (JamesandCrow, 1986).The importance of accurate temperaturecontrolat this stageis not alwaysrecognisedand,at worst, product may be tempered wherever there is spacein the factory at ambient temperatures. The main advantageof microwavetempering is speed;it also requires less space.Experiments carried out at Bristol demonstrate that frozen blocks, processed directly from frozenstorage, canbetemperedin aboutfive minutesto ÿ3ºC(0 toÿ5ºC),using a 30kW,896MHz microwave(JamesandCrow,1986). Because it is difficult to meetthe targettemperature consistently,theremay be occasions when the meat is either under-tempered (i.e. too cold) or over tempered(i.e. too warm), leading to variability in particlesizedistribution and product quality (Koberna, 1986). 17.2.3 Pre-breaking A variety of designsof pre-breakerexist suchas chippers,flakers,guillotines and grinders.These differ markedly in the mode of action but all effect a reduction in size sufficient for further processing.In the UK pre-breakingby grinding is probably the most common, using a kidney-shapedprebreak plate and‘kni fe’. Most modelsrequirethe meat to be temperedbeforepre-breaking. However, thereis an attraction of pre-breaking blocksdirectly from the freezer storeandthe more powerful machinescando so,but at the expenseof product quality. Productcohesivenessis adversely affected whenmeatis pre-broken by grinding at low temperatures,and accompanied by increased cooking losses (Ellery, 1985; Jolley et al., 1986), probably through damage to fat cells generating more liquid fat during cooking (Evansand Ranken,1975), which could interfere with productcohesiveness(Jolley andPurslow, 1988). Processing andquality control of restructuredmeat 335 17.2.4 Flaking Flaking appearsto be the methodof choice for grillsteak manufacture,though ostensibly thereis no reason why other methods of comminution could not be used.Comminution by flaking is relatively new,theequipmentbeingdeveloped in the 1960s by Urschel International, based on Comitrol machinesused originally for cutting, slicing and dicing vegetables. The main purpose of comminution is to reduce the sizeof sinewandgristle,which would otherwise result in objectionable toughness. Fat is also comminuted and not easily discernible in the final product,especially usingsmallerflaking heads, evenat high fat contents. Cutting is effectedby animpeller thatrotatesat 3000rpm (50 revsa sec)and forces meat against a stationary cutting head (Fig. 17.2). The severity of comminution canbe controlled by selectingthe appropriatecutting headwhich canvary in aperturesize(ranging from 60 to 1600thousandthsof an inch, i.e., 1.5 to 40.6mm) and the numberof cutting stations (Anon., 1980). It is usual, where meatsof different quality areused,to usea smalleraperture size( watermaybeusedto compensatefor evaporative lossesduringprocessing,with little effect on eating quality or cook losses.Salt and phosphate have a synergistic effect when usedtogether, usually at a ratio of about1:4. Flavour constraints limit the amountof salt that canbe addedto about1.5%. Initially the comminutedmeat mass is relatively free flowing but asmixing proceedsbecomestackyandtends to ‘ball together’ due,presumably,to protein extraction. Mixing timesvary but typically arearound five minutes,depending on the productand type of mixer. This allows sufficient time to distribute any addedingredients uniformly throughthe meatmass and,more importantly, to solubilise myofibrillar proteins.Thoughit is difficul t to prove,using analytical techniques, protein solubilisation can be inferred from the clear effects that addedsalt hason cooking lossesandcohesive strength. Shortmixing timesareusually associatedwith a loose,friable texture whilst excessive mixing times usually result in an objectionably rubbery texture. Optimal mixing timesareusuallydetermined by trial anderror or a subjective appraisal of the appearance of the mix. Invariably, optimal mixing times vary from experiment to experiment (Booren et al., 1981a,b; Coon et al., 1983; Durland et al., 1982;Noble et al., 1985;PepperandSchmidt,1975) indicating that the ‘best’ mixing time may dependupon the propertiesof the meat being mixed andalsovary from machineto machine. 17.2.6 Forming The useof a high-speedpatty former is the most popular means of imparting shapeto the finishedproduct and achieving accurate portion control. A wide rangeof formers are available but all operate on roughly similar principles, employing a reciprocating mould plate and a means of transferring the meat from a hopperandto themould. Mould plates(round, steakor rib-shaped,etc.) can be changed according to the product required.Most formers operatewell over a relatively small temperature range, outside of which weight control becomesmore variableandproductcanbecome ragged(Koberna, 1986).This presumably is related to the influenceof temperatureon the viscosity andflow behaviourof the meatmass. An alternativemethodof forming is to extrudethe meatinto a log which is then tempered and sliced, as required. In the production of Bernard Matthews turkeyroasts,leanturkeymeatis co-extrudedwith a coating of fat in cylindrical form for subdivision into joints or steaks.Some products may be battered, coatedandfried. 17.2.7 Freezing Salt doesnot produce a good bind in the raw stateand so most products are therefore frozen, usually cryogenically, using liquid nitrogen or liquid carbon dioxide, sprayed onto the food. Cryogenic freezing is rapid and has the advantageof reducing evaporativelosses (Tomlins, 1995). However, it is Processing andquality control of restructuredmeat 337 expensive and some companies now use conventional blast freezing and compensatefor the higher evaporative lossesby adding water. Salt is a pro-oxidant increasing the rateof lipid oxidation (see,for example, Chen et al., 1984) and also discolouration. Even at freezertemperatures,salt- treated comminutedmeatcandiscolour within a few dayssomostproducts are packaged in cardboard outers. Frozen product can usually be stored for up to threemonths,without any adverseeffectson flavour dueto lipid oxidation. 17.3 Factors affecting product quality: temperature, ice content, particle sizeand mechanicalpropert ies Conceptually, a restructuredmeat product can be viewed as comprising meat pieces in a matrix of solubilised meatprotein (Fig. 17.3). This model, though simplistic, suggests three key factors that might affect eating quality: (i) the nature of theparticles (their size,shape, surfacemorphologyandfibre direction) including their orientationandcomposition,(ii) the amountandcomposition of the exudateand (iii) the relative proportion of piecesto matrix. Thus, some authorshavesuggested‘optimal’ size reductionand‘optimal’ adhesion between meat pieces(’bind’ ) to be key determinants of product quality (Jolley and Purslow,1988).In orderto controlandmanipulateparticlesizeandadhesion,it Fig. 17.3 Schematicdiagramof a restructuredmeatproduct(Adaptedfrom Jolley and Purslow,1988). 338 Meat processing is importantto understandthe factors affecting them.As well ashavinga direct effect on eatingquality, particlesizealsoaffectstheappearanceof theproduct, andthe available surfaceareafor protein extraction. In grillsteakmanufacture, the size reduction is a two-stage operation, involving pre-breaking (which achievesa relatively coarsecomminution) and flaking (a fine comminution). The temperature of the meat is critical becauseof its effectson ice content and mechanical properties. 17.3.1 Ice content Leanmeatat slaughter containsabout75%water.The proportion which freezes depends on thetemperatureandcanbeexpressedby theequation I ˆ 1ÿ ifp=T whereI is the fraction of freezablewater,ifp is the initial freezingpoint (about ÿ1ºC in lean meat)andT is the temperature in ºC (Fig. 17.4).The rationale for this behaviouris that solutesnaturally present in the meatreduce the freezing point and these becomeprogressively concentrated in the unfrozen liquor, resultingin an ionic strength of about1M atÿ5ºCand2M atÿ15ºC(Offer and Knight, 1988b). It is evident from Fig. 17.4 that some water remainsunfrozen evenat very low temperatures(< ÿ30ºC); also, the ice content changesmost rapidly betweenÿ1 andÿ10ºC, i.e., the temperature rangein which processing takesplace. Salt causes a depression of the initi al freezing point (Table 17.1) which hasa markedeffect on ice content (Fig. 17.4). Fig. 17.4 Relationshipbetweenice content(I) andtemperature(T) for leanbeefat initial freezingpoints(ifp) of ÿ1, ÿ2, ÿ3 andÿ4ºC calculatedusingthe expression Iˆ (1ÿifp/T)100%. Processing andquality control of restructuredmeat 339 17.3.2 Changes in ice content and temperature during processing Temperaturesusually riseduring processing,whilst theice content falls (Sheard et al., 1989,1990b,1991a,b). However,the ifp is loweredby theaddition of salt during mixing – causing ice to melt – and it is not uncommon to see the temperaturefall by 0.5 to 1ºC during mixing with salt (Sheard et al., 1990c).

Temperaturesat the endof mixing andforming aretypically around ÿ2ºC and unlikely to rise much above this unless product has been standing for long periods due to equipmentfailure. Differencesin pre-breaking temperature can lead to relatively large differencesin ice contentat the end of the processing line, though differences in temperaturesareonly small anddifficult to measure. Small temperaturedifferencesat theendof theprocessingline oftenreflectlarge variability in temperatureat thebeginning of theline. Unlesstemperatureis well controlled at the tempering andpre-breakstage,variation in productquality can be expected. Temperature measurementsat the tempering stageare therefore essential for quality control purposes. 17.3.3 Sizereduction The factors influencing particle size havebeenreviewed elsewhere(Sheard et al., 1990a),aresummarisedin Table17.2andillustratedin Table17.3.Particle size was measured by collecting particles on a preweighed perspex sheet, analysedusinga video imageanalysistechniqueandpresentedin variousways (size distribution, number of particles per g, surface area per g or mean thickness).The techniqueis rapidandpowerful providing particlesarediscrete; if not, as with mince, particle size may be measured using a wet sieving technique(Sheardet al., 1991a). Meat pre-broken by grinding ranged in sizefrom tiny fragmentsof lessthan 1mm in diameterto large, irregularly shaped piecesapproximately 4–5cm in diameter (Ellery, 1985;Sheardet al., 1989).Temperaturehada majoreffecton particle size (Sheard et al., 1989, 1990b), even small differences (ÿ5 and ÿ3.5ºC) leadingto significant differences in particle size(Sheard et al., 1989); lower temperaturesproducinga largerproportionof smallerparticles.Thereis a lack of informationon thecharacteristicsof particlesproducedby othermethods of pre-breaking. Table 17.1 Effect of sodium chloride and sodium tripolyphosphateon the initial freezingpoint (ºC) of meat(Sheardet al., 1990c) Phosphatelevel (%) Sodiumchloride level (%) 0 1.0 4.0 means 0 ÿ0.82 ÿ1.53 ÿ4.24 ÿ2.20 0.25 ÿ0.96 ÿ1.57 ÿ4.31 ÿ2.28 0.50 ÿ0.92 ÿ1.82 ÿ4.46 ÿ2.40 means ÿ0.90 ÿ1.64 ÿ4.34 ÿ2.29 340 Meat processing Compared to meatpre-brokenby grinding, flaking resultsin a hugeincrease in the number and surfaceareaof particles (Table 17.3). Individual particles may be fractions of a mm thick (i.e. only a few fibres thick), ranging from 1ºCproducesmincelikestrands(Sheardet al., 1990a,b). Pre-breaking Major effect. Meat pre-brokenby grinding breaksup far morereadily thanintact meatpieces(Sheardet al., 1990b) Meat species Small differencesbetweenleanbeef,turkey breastand turkey thigh meat(Sheardet al., 1990a) Numberof cutting stations Affects particle thickness(Sheardet al., 1991a) Impeller speedanddesign Minor effects(Sheardet al., 1991a) Table 17.3 Particlesizeof meatpre-brokenby grinding atÿ3 andÿ7ºC, retempered andthenflaked atÿ3 andÿ7ºC (Adaptedfrom Sheardet al., 1990b) Methodof temp aperturesize no./g area/g thickness comminution (ºC) (mm) (mm2/g) (mm) Pre-breaking ÿ7 ÿ 2.7 410 ÿ ÿ3 ÿ 0.8 221 ÿ Flaking ÿ7 6.1 368 2420 0.43 19.0 108 1251 0.80 ÿ3 6.1 164 939 1.08 19.0 30 651 1.55 Processing andquality control of restructuredmeat 341 1991a). The useof high-speedphotography illustratesthis differencein cutting action very clearly. At low temperatures,individualpiecesof meat arecut very quickly (within about a third of a revolution or 0.007s) but at higher temperaturesindividual piecesdeformagainstthe cutting headandarecarried around the inside of the flaking headfor many revolutions without being cut before emerging asmince-like strands(Sheard et al., 1990a). 17.3.4 Mechanical properties In order to understandand predict the effects of high-speedprocessingon the behaviour of meatduring comminution, variousauthors have investigatedthe mechanicalpropertiesandfracturebehaviourof meatunderdifferentconditions, to determine tensile strength, work of fracture and other properties using traditional waysemployedby materials scientists(Munro,1983;Dobraszczyket al., 1987). In common with many biological materials (Ashby, 1983; Atkins, 1987; Atkins and Mai, 1986), the mechanicalproperties of meat dependon temperature,watercontent (or ice content), thestrainrate(i.e. the rateat which the sample is deformed) and the fibre direction (Dobraszczyk et al., 1987; Munro, 1983;Purslow,1985).At low temperatures(< ÿ15ºC)meat behavesin a brittle way (breakingsuddenly in sucha way that the broken endsmay be refitted to regainessentially the original dimensions) but exhibits viscoelastic behavour (in which samples exhibit extensive deformation before eventual fracture)at higher temperatures(> ÿ10ºC) (Dobraszczyket al., 1987;Munro, 1983).Water, it seems,actsasa plasticiser,allowing thematerial to deform to a greater extentbefore fracturing (Atkins, 1987).Munro (1983)showedthatmeat is highly anisotropic (i.e. the structureandproperties of the material dependon fibre direction) abovethe ifp but only slightly sobelow the ifp wheretheratio of tensile strengthsfalls from 5:1 (above the ifp) to 2:1. This observation is important because a highly anisotropic material is more likely to produce particles with a preferred fibre direction than a material that is isotropic or slightly anisotropic. Brittle behaviouris favoured by high strain rates(Atkins and Mai, 1986), though most workers haveusedstrain ratesmuchlower thanthose encountered during meatprocessing(Dobraszczyk et al., 1987;Munro,1983).Recentresults from this laboratory,usinga Charpy impacttest,andstrain ratescomparable to those used in high-speed comminuting equipment, are shown in Fig. 17.5. Below ÿ10ºC fracture was complete and, from the surface appearance, specimensapparently failed in a brittle fashion.At intermediate temperatures (ÿ10 to ÿ5ºC), fracturewascompletebut wasaccompanied by an increasein the amountof energyabsorbed which can be attributed to an increase in the amount of energy absorbedplastically, resultingin greater deformation.At still higher temperatures(> ÿ5ºC), fracture wasincomplete, andnon-existentatÿ2 to ÿ3ºC whenspecimensmerely deflected on impact. Therewasan anisotropy of impactenergy according to fibre orientationof about2:1; this is far lessthan in thawed (Munro, 1983) or cooked meat (Purslow, 1985) and is probably 342 Meat processing insufficient to resultin a preferredfibre directionduringcomminution.It canbe inferred that at low temperatures(ÿ10ºC) fracture is easily inducedbut poorly controlled, leadingto shattering; at high temperatures (closeto the ifp) fracture is difficult to induce without causing extensive deformation, whilst at intermediate temperatures(ÿ5 to ÿ10ºC) fracture can be induced but without causingextensiveshattering and is therefore easierto control. 17.4 Factors affecting product quality: protein solubility and related effects As mentioned earlier, the re-assembly of meat pieces once they have been comminutedis anessential requirementin restructuring. Goodadhesion (‘bind’ ) between meat piecesis widely regardedasa key determinantof quality, usually achievedby adding salt, sometimes in conjunction with phosphate,addeddry during mixing. Other meansof achieving adhesion are discussed later. In addition to its effect on adhesion, salt also increaseswater retention, reduces cooking losses and may also increase tendernessslightly. The underlying mechanism involves depolymerisation of myosin and dissociation of actomyosin, at appropriate concentrations, which in turn (i) allows expansion of the myofibrillar lattice (Offer and Knight, 1988a), thus improving water retention characteristics and reducing weight loss on cooking, (ii) effects adhesion on cooking via gelation of the solubilised myosin which binds the constituent meatpiecestogether and(iii ) effectsa tenderisation partly dueto the Fig. 17.5 Effect of sub-zerotemperaturesandfibre directionon energyabsorbedduring Charpyimpact testingof frozenandsemi-frozenmeat. Processing andquality control of restructuredmeat 343 increased water retention and partly as a result of the disassembly of the myofibrillar filaments. In orderto control andmanipulatethebeneficial action of saltandphosphate on the propertiesof restructuredmeats, it is importantto understandthe factors affecting them (Table 17.4). Thesehave been reviewed in detail elsewhere (Jolley andPurslow,1988)andneednot becoveredhere, other thanto highlight the following issues. 17.4.1 Effective salt concentration Myosin is the most abundant muscle protein (Lawrie, 1998) and exists as discrete thick filaments in the myofibril. Its solubility with respect to ionic strength andpH havebeeninvestigatedwidely andit is well known thatmyosin is insolubleat physiological ionic strength (0.15ÿ0.2M) andhigh ionic strengths but soluble at intermediateionic strengths0.3ÿ0.6M at pH 5.5. This behaviour of myosin producesa curvilinearrelationship with increasingsaltconcentration: with zero extraction at very low and high ionic strengths and maximum extraction at 5ÿ10% NaCl (Bard, 1965;Callow, 1932;GrabowskaandHamm, 1979) i.e., much higher salt levels than those found in restructured meats. Similar relationshipswith increasing salt concentration have been found for Table 17.4 Factorsaffecting the extraction of myofibrillar protein from meat and adhesionbetweenmeatpieces Propertiesof raw meatingredients Rigor state Myofibrillar proteinsmoreeasilyextractedin prerigorstate Muscle type Poorquality meatshavelow salt extractableproteincontents (Saffle andGalbreath,1964) Freshor frozen Conflicting results(e.g.compareSaffle andGalbreath,1964 andActon andSaffle, 1969) Processingconditions Particlesize Reducingmeatparticlesize improvesproteinextraction (Acton, 1972) Extractiontime More proteinextractionat longer times Temperature Conflicting results(compareBard,1965andGillet et al., 1977) Addition of salt Causesdepolymerisationof myosinanddissociationof actomyosinat appropriateconcentrations Addition of phosphate Causesdepolymerisationanddissociation,after enzymic hydrolysisto pyrophosphate,the active form. Hydrolysisat 0ºC is slow Adhesion Proteintype Myosin is betterthanactomyosin.Sarcoplasmicproteinshave little adhesivestrength Fibre orientation 90/90betterthan0/0 or 90/0 344 Meat processing water holding and cooking loss (Callow, 1932; Wierbicki et al., 1957). Other studiesin model systemshaveshown thatmeatswelling is a highly co-operative phenomenom and no myosin extraction occurs below 0.6M (i.e. about 3% sodium chloride (Offer and Trinick, 1983). It seemsreasonable, therefore,to question the assumption that myosin is solubilised in restructuredmeatswhere the salt concentration, 0.5–1% (0.17M), is much lower than the minimum required to evince any myosinextraction. This apparent conflict hasbeenresolved by arguing that the effective salt concentration during mixing is much higher than to be expected on a simple weight basisdue to localisedsalt concentrations,particularly during the initial stagesof mixing (Jolley and Purslow, 1988). Complete equilibration of salt within the time allowed for mixing, typically about five minutes, is unlikely giventhatsalt diffusion throughmeat is slow (Sheard et al., 1990c).In addition, this concentrative effect would be exacerbatedbelow the initial freezing point whenlargequantities of waterarepresentasice and,therefore,unavailableasa solvent. In otherwords,comparisonsbetween model systems andtheconditions pertaining during manufacture are quite different due to differencesin the solvent:meatratio. Given the observableeffectsof addedsalt on meat binding, water holding and cooking losses (seelater), it seemshighly likely, therefore, thatsome,thoughnot necessarily

maximal, protein extraction occurs during the manufacture of restructured meats. 17.4.2 Effect of temperature The influenceof temperatureon the extractability of muscleprotein hasbeena matterof some controversy. Gillett et al. (1977) found that maximum protein extraction at 7ºC,wasabouta third higherthanatÿ4ºCor 20ºC,suggesting that processing above the ifp may be beneficial as far as protein extraction is concerned. By contrast, Bard (1965) reportedmaximum protein extraction at ÿ5ºC, with a two- to three-fold reduction at 0ºC. Recent data from this laboratory, investigating the influence of temperature(ÿ7 to 15ºC) acrossa range of salt concentrations (0 to 5M), is helpful in understanding these contradictory results. The amountof protein solubilised increased from about 1mg/ml at 0M NaCl to a maximum at 2M NaCl which declinedat highersalt concentrations (Fig 17.6). At 2M NaCl, salt-induced protein solubilisation increasedwith decreasingtemperaturebut this relationshipdid not apply at most othersalt concentrations. 17.4.3 Phosphatehydrolysis Phosphate,like salt, is a mild structure breaker but its chemistry is more complicated.Thoughit canbeusedalone to improve waterretention,juicinessand tendernessat levels of 0.25–5g/100g (Sheardet al., 1999),in restructuredmeatsit is usually used in conjunction with salt. Commercial mixtures may include pyrophosphate and tripolyphosphate as well as longer chain and cyclical Processing andquality control of restructuredmeat 345 phosphates(Iles, 1973). The active form is believed to be pyrophosphate(the diphosphateform, (P2O7) 4ÿ) (Yasui et al., 1964) which is producedby hydrolysis from tripolyphosphate((P3O10) 5ÿ) andis itself hydrolysed to orthophosphate(the monophosphateform, PO4 3ÿ). Thehydrolysisdependson pH, temperatureandthe ionic species. In beef,the tripolyphosphatase activity of myosinis about15 times that of the diphosphataseactivity (Neraal and Hamm, 1973), thus favouring the formation of the active form, pyrophosphate. The pH optima for tripolyphosphataseand diphosphatase,5.6 and 6.7 respectively, likewise favours theformationof pyrophosphateat thenormalultimatemeatpH (about5.5),asdoes sodium chloridewhich increasesthe tripolyphosphataseactivity but decreasesthe diphosphataseactivity (Belton et al., 1987;NeraalandHamm,1973).The rateof hydrolysis doubles with every 10ºC rise until above 40ºC the enzyme is progressively denatured (Neraal and Hamm, 1973). At 20ºC, 0.5% tripolyphosphate is brokendown in about8 to 20minutes,whilst 0.5%diphosphate requires 2 to 15 hours(Neraal and Hamm, 1973). The hydrolysis appearsto be much slowerat 0ºC(Neraal andHamm,1973; Sutton1973). Giventheabove, one might not expectthe hydrolysisto orthophosphateto be completewithin normal processingtimesthough it seems thereis sufficient pyrophosphate, even at 0ºC,to exert measurableeffectson meat binding, cook loss andotherproperties. 17.4.4 Adhesion Studies,using ‘model’ adhesive junctions, in which the adhesive is sandwiched between two meatpieces,haveshownthat myosin is a strongeradhesive than actomyosin (Macfarlaneet al., 1977) and that the strengthof the joint varies with the orientationof the musclefibre (Purslowet al., 1987). It seemsli kely that thebindingstrengthof restructuredmeat products will bedeterminedby the weaker junctionswhich will bethefirst to fail duringmastication. Sarcoplasmic Fig. 17.6 Effect of temperatureon the amountof proteinsolubilisedfrom meatin different concentrationsof sodiumchloride(from SheardandSavage,1998). 346 Meat processing proteinsarepoorbinders andprobablyplay little part in meatbindingexcept in situations where little or no myofibrillar protein is solublised (Jolley and Purslow, 1988). However, acceptable products can be produced without the additionof salt or phosphate. In this case,adhesionis probably achievedpartly by physicalentanglementpiecesandthe aggregationof sarcoplasmic proteins. 17.4.5 Cooking losses Cookinglossesareimportantbecausecooklossnot only affects thefinal weight and,therefore,portion sizebut also the perceived juicinessof the product and possibly texture as well. Losses can vary widely depending on product formulation, the conditions of processingandthe cooking method.For a given cooking method,salt and phosphate levels are probably the most important factors (Mandigo,1982;Moore et al., 1976)and,together, they havea marked effect on weight loss during cooking (Table 17.5), thoughsalt hasan adverse effecton thedevelopmentof oxidativerancidity (Table17.6).The typeof meat is alsoimportant(Table17.7),possibly becausemoremyosin is extractedfrom white fibresthanredfibresunderequivalentconditionsof ionic strength andpH (Xiong, 1994; Xiong andBrekke, 1989). 17.5 Factors affecting product quality: cooking distortion Cookingdistortion is a persistentproblemwith products – including burgers and grillsteaks – formed using a high-speedpatty former (Jolley and Rangeley, Table 17.5 Effect of sodiumchloride andsodiumtripolyphosphate(TPP)on cooking losses(%) from beefgrillsteaks(Adaptedfrom Sheardet al., 1990c) TPPlevel (%) NaCl level (%) 0 0.5 1.0 2.0 4.0 means 0 34.8 33.0 31.9 31.3 31.2 32.4 0.25 33.0 31.5 25.8 25.6 26.7 28.5 0.50 29.2 25.6 24.8 23.1 25.7 25.7 means 32.2 30.0 27.5 26.7 27.9 28.9 Table 17.6 Effect of salton TBA valuesandcookinglosseson cookedpork grillsteaks (Adaptedfrom SchwartzandMandigo,1976) Salt (%) 0 0.75 1.50 2.25 TBAa 0.11 0.50 0.84 0.94 Cooking loss(%) 37.5 21.0 14.6 13.4 a mg malonaldehydeper kg meat Processing andquality control of restructuredmeat 347 1986).Themost commontype is mostreadily seenin burgers that,on cooking, shrink preferentially in one direction and, thus, adopt an oval shape. This is sometimesreferredto asunevenlateralshrinkage.Usingultraviolet light (which causes fat and connective tissue to fluoresce), Mounsdon and Jolley (1987) demonstratedthat lateral shrinkage is dueto alignment of connective tissueon thesurfaceof theproduct. This wasattributed to friction generatedbetweenthe surface of the product and the reciprocating plate during patty forming. On cooking, the connective tissue shrinks, generating tension and leading to preferentialproduct shrinkage in the direction of alignment. Shrinkageduring cookingcanalsoleadto an increase in height(doming) of theproduct andthedevelopmentof anair-fil ledvacuolewithin themiddleof the product. Sometimes fluid accumulatesin thevacuole,a phenomenon sometimes referred to as ‘welling’. Doming and welling are less common than lateral shrinkage,morevariablein nature anddifficult to control.Sometypes of flame- grilled grillsteaks seem especially vulnerable to distortion. The causesof doming andwelling wereinvestigatedin two factory-basedtrials conducted by JolleyandRangeley(1986). Selected resultsfrom the first trial, shown in Table 17.8,demonstratethatall pattiesshrankmorealongthebase(27–35%) thanthe width (14–21%), indicatingthat theconnectivetissuewasalignedpreferentially along the lengthof theproduct. Theheight increasein theworstcasewas41%, with fluid losses on puncturing up to 6.7g. The largest single influence on distortion was the design of patty former (of the two formers used,one was significantly worsethan the other), though the causeswere highly interactive (Table 17.9). This explains why the problemsare not easy to control and suggests that the results obtained in one systemmay not necessarily apply elsewheredueto machine specificity. Perhapsmore importantly, theresults also indicate potential difficul ties in scaling up from laboratory-based trials to factory conditions. Thus, optimal conditions pertaining under laboratory conditions may not be optimal in the factory situation. Table 17.7 Cookinglosses(%) from UK-style grillsteaksmadefrom beefforequarter, turkey breast and turkey thigh meat formulated with salt (0 or 0.75%), sodium tripolyphosphate(TPP) (0 and 0.25%) and water (0 and 2%) (University of Bristol, unpublisheddata) Treatment Beef Breast Thigh Means None 32.7 22.8 29.6 29.4 Water 37.4 23.0 32.2 31.6 Salt 26.6 20.2 22.1 24.0 TPP 29.7 18.0 23.7 24.3 Water+ salt 28.6 20.0 21.8 24.1 Water+TPP 29.7 22.9 25.7 26.8 Salt + TPP 25.4 18.8 17.9 20.6 Water+ salt +TPP 23.6 20.5 20.2 21.9 Means 30.2 20.8 25.0 25.3 348 Meat processing In addition to theconditionspertaining duringmanufacture,cooking method, cook temperature and product thicknessare also important factors (Campbell and Mandigo, 1978; Campbell et al., 1977), presumably becauseof their influence on timetemperatureregimesduring cooking and, thus, the rate of shrinkage. Thicker products were more proneto height increase, especially at higher temperatures(Table17.10). 17.6 Sensoryand consumertesting A wide rangeof sensorytests– ranking, category and profiling techniques– havebeenusedto assessthe tactile, appearance, texture, flavour, juicinessand hedonic (i.e. liking) attributesof restructured meats (e.g. Berry and Civille, 1986; Cardello et al., 1983; Ford et al., 1978). The textureprofiles that have beendeveloped(e.g.Berry andCiville, 1986;Cardelloet al., 1983;Savageet al., 1990)usesimilar descriptors to thosedevelopedfor burgers (e.g.Berry and Leddy,1984;Dransfield et al., 1985).Several authors,of which Cardello et al. (1983)andBerry et al. (1987)arethemost convincing,haveshownthat texture, Table 17.8 Effect of former type (1 and2), delaybetweenblendingandforming (0 or 35 min.) andeffectivenessof freezing(‘fast’, ‘slow’) on dimensionalchangesandweight of fluid collectedon puncturing(welling) for UK-style grillsteaks(Jolley andRangeley, 1986with permission) Former 1 2 Delay (min.) 0 35 0 35 Freezingrate fast slow fast slow fast slow fast slow Shrinkage,base(%) 30 31 35 32 28 29 27 27 Shrinkage,width (%) 15 21 22 20 14 14 16 14 Doming (%) 23 31 41 33 12 14 8 9 Welling (g) 3.1 6.7 3.3 6.4 2.0 1.6 1.6 1.2 Table 17.9 Level of significanceof main and primary effects (Jolley and Rangeley, 1986with permission) Former Delay Freezing Former Former Delay delay freezing freezing Shrinkage,base(%) *** Shrinkage,width (%) *** X (X) ** Doming (%) X (X) (X) *** * Welling (g) X X *** * p appearanceand acceptability, as assessedby a trainedsensory panel,depends uponaperturesize. Fatbecomeslessdetectablevisibly with decreasingaperture size, as does the amount of connective tissueperceived during mastication. Otherstudieshaveshownthat productcohesion,amongother factors, depends uponthe level of salt or addedmyosin(Ford et al., 1978;Savageet al., 1990), with perceived rubberiness increasing with level of myosin. As might be expected,juicinessandmoisturerelease increasewith increasingfat level (Berry et al., 1985). Consumer tests, involving large numbers (typically in excess of 100) of untrainedassessors,areconcernedprimarily with preferenceor liking decisions (Nute,1996).In onetrial, theadhesionbetween meatpieceswassystematically variedby adding differentconcentrationsof crudemyosin (0, 1.75,3.5,5.25and 7% protein) (Savage et al., 1990). Tensile adhesive strengthmeasurements increased almost linearly with increasinglevels of addedmyosin. However, consumer preferencevariedbetweenindividuals; some preferred weakly bound products whilst otherspreferredproducts that were strongly bound,and there wasno overall preferencefor any oneproduct.Clearly, these resultschallenge the assumption that an increase in adhesionnecessarily results in a ‘better’ product. In another trial (Nute et al., 1988),eight formulationsof restructuredsteaks wereassessedfor

texture, saltiness,juiciness, taste, meatinessandoverall liking by consumers in two regionsof the UK (north andsouth).Steaks varied in fat level (12 and20%),salt level (0.5 and1%), temper(long andshort) andmixing time (6 or 12 mins.).Analysis of variance revealedthat consumers wereableto perceivedifferences in saltinessandjuiciness, althoughtherewasno significant differencein overall liking. However, internal preferencemapping showedthat consumers in the southcould be segmentedinto four categoriesaccordingto their preferencefor fat andsalt level (high fat andhighsalt, high fat andlow salt, low fat andhigh salt, low fat and low salt). In anothertrial, consumers were askedto evaluaterestructured beef steaks made using different aperture sizes,rangingfrom 1.5 mm to 40.6mm(Cardello Table 17.10 Influenceof product thicknessand cooking temperatureon dimensional changesandweight lossesin restructuredpork pattiescookedto 77ºCon a rotaryhearth oven(Adaptedfrom Campbellet al., 1977) Portionthickness(cm) 1.27 1.90 2.54 Thickness(%) 106.8 110.9 113.0 Cook loss(%) 40.5 35.6 31.9 Cook temperature(ºC) 149 177 205 233 261 Thickness(%) 97.5 107.6 113.4 115.0 117.5 Cook loss(%) 36.8 32.9 37.2 35.7 37.3 350 Meat processing et al., 1983). All the flaked productswere regardedas being different from groundbeefpattiesand,also, from intact muscle(ribeyesteak).However, there was no significant differencein overall acceptability, acceptability of texture, flavour or appearance between any of the flaked products, despite the large rangeof aperturesizesused,andit is tempting to speculate that this, too, is due to differencesin consumerpreference. Taken together these trials challengethe idea of generating an ‘optimal’ product (in termsof separatecharacteristics suchasbind, texture, or flavour or, indeed,in termsof the product’soverall characteristics) sinceconsumersvary markedly in their individual preferences.Of course,thereis considerablescope for generatingproducts with particular characteristics(e.g.a goodbind or a firm bite) and marketing these in such a way to target certain segmentsof the population in orderto matchproductcharacteristics with individual preferences. 17.7 Future trends 17.7.1 Fresh product Salt is the ingredientof choiceto bind restructuredmeats. Thereis, however, growing consumerpressure against the use of salt in foodstuffs, for medical reasons.Technically, also, salt has its drawbacks, being a pro-oxidant it acceleratesthe production of metmyoglobin, thusreducingcolour stability and acceleratestherateof lipid oxidation. This,andthefact thatproductcohesion is poor in the raw state,effectively precludesthe marketing of restructured meats in the chilled state.Among consumers thereis a perception that fresh is better thanfrozenandconsumersarewilling to pay a premium for freshproduct. Thepotential to marketgrillsteak-typeproducts in thefreshstateis illustrated by the growth in sales of freshly chilled burgerswhosemanufacture is very similar to that of grillsteaks, and, like grillsteaks,traditionally havesold in a frozenform. In developing a market for freshgrillsteaktypeproducts, themain requirement is to maintain colour stability andminimisebacterialgrowth. The formercanbeachievedsatisfactorily by usingalternativebinders to salt,thatdo not accelerate the formation of metmyoglobin, and using an appropriate packaging systemto extendthe colour shelf-life (e.g. a modified atmosphere packcontaining 70%oxygenand30%carbon dioxide). Bacterialgrowthcanbe minimisedby usingsodiumbisulphite. Oneinnovativesolutionto overcoming theseproblems involvestheuseof the polysaccharidesodiumalginate,whose usein meat for this applicationwasfirst advocatedin thepatent of SchmidtandMeans (1986). Cross-linking is achieved chemically, rather than thermally, between divalent cations, usually calcium, andtheguluronicacidmoitiesof alginate.Products made usingalginate,packed undermodifiedatmospheres retain a bright red, freshcolour for at least a week storedat2ºC(Richardsonetal., 1989).Theprocessworksbestabovetheifp, but once gel formation is complete, products can be frozen without impairing product cohesion. Therateof bind development,andits ultimate strength,in the Processing andquality control of restructuredmeat 351 raw andcookedstate,canbecontrolled by the type of calcium salt, theamount of addedalginateandalginatetype(Trout,1989;Richardsonet al., 1989).Weak acids suchas citric acid or lactic acid can also be usedto control the rate of gelation by acceleratingthe release of calcium. Althoughglucono-delta-lactone (gdl) is not itself acidic, it may also be usedfor this purpose as it is slowly hydrolysedin meat to gluconicacid; gdl alsopreventstheundesirableafter-taste sometimesexperiencedwith thealginate/CaCO3 systemdescribedby Meansand Schmidt (1986). The rate of gelationmust be suchthat the gel is not broken down during mixing and forming (Richardsonet al., 1989). It is desirable to avoid theuseof sodiumchloride asthis interfereswith thedevelopmentof bind, asdoescollagen (Richardsonet al., 1989). Anothersystemcapable of producing cohesion in the raw stateinvolvesthe useof extractedplasmathrombin andfibrinogen(WijngaardsandPaardekooper, 1988). This ingenious application of the blood clotting mechanism was developed at the Netherlands Centre for Meat Technology. Gel formation is the result of the conversion of fibrinogen into fibrin by the enzymethrombin. Fibrin molecules, in turn, becomecovalently cross-linked by the action of transglutaminase, present in the partially purified fibrinogen,which alsocross- links fibrin and collagen. An advantageof this system is that a well bound product canbemadeevenwherethereis a high level of collagen.Gel formation is complete in about12hoursdependingon temperatureandpH, theultimategel strength being determined by the fibrin concentration. A third systememploys purified transglutaminase (Kuraishi et al., 1997; Nonaka et al., 1989).Thoughrelatively expensive, it is very effective binder. The enzyme may be addeddry, using casein asa carrier, or addedwith water. The rate of bind developmentdepends on enzymeconcentration, temperature andtime. At chill temperatures,bind developsin threeto six hours. 17.7.2 Engineered texture Most processdevelopmentandproduct formulation hasbeenlargely empirical, on a trial and error basis,without any real understanding of the underlying principlesthatgovern endproductquality. However,thereareexceptionswhich deliberately set to out to overcome some of the obstacles encountered in developing a comminuted product with a steak-like texture. Theseso-called ‘secondgeneration’products (Jolley et al., 1988),apparentlybasedon thepatent application of Bradshaw and Hughes (1986), overtly claim to havesteak-like characteristics. They comprise a ‘texture-imparting’ phaseof relatively large pieces and a ‘succulence-imparting’ phase of finely comminuted meat, presumablya lower graderaw material havinga higher fat content. Alignment of the piecesreputedlyoccurs during forming. Thoughexamples like this are few, the very fact that suchproducts havebeendevelopedis encouraging and augurs well for the future. 352 Meat processing 17.8 Sourcesof further infor mation and advice This chapterhasconsidered the processingof restructured meats,a subjectthat hasbeenreviewed extensively elsewhere(Franklin andCross,1982;Jolley and Purslow, 1988; Pearsonand Dutson, 1987; Sheard and Savage, 1998). In conclusion it is worth emphasisingfour points. 1. Good control over temperature is vital when processingbelow the ifp to avoid variability in productcontrol. Practically, this is achievedby good temperature control at the start of the processing line (i.e. at the temperature/pre-breakstage)andkeepingconditionsconstantat laterstages of processing. 2. Somequality problemsare highly interactive and machine specific and, therefore, diffi cult to control. The resultsobtained in onesystemneednot necessarily apply underother conditions. 3. There are enormous obstacles to producing a steak-like texture and this goal, perhaps, is unattainable using existing methodsof comminution, mixing andforming. 4. Consumersvary widely in their individualpreferences– for degreeof bind, optimal level of fat andsalt,etc.– andthereis scopefor targeting segments of the population to match product characteristics with their particular preferences. 17.9 References ACTON J C (1972), ‘The effect of meat particle size on extractableprotein, cookinglossandbindingstrength in chickenloaves’,J FoodSci, 37,240– 243. ANON. (1980),Facts,flakesand fabricated meats, Urschel LabsInc. ASHBY M F (1983), ‘The mechanicalpropertiesof cellular solids’, Metallurgical TransA, 14A, 1755–1768. ATKINS A G (1987), ‘The basic principles of mechanical failure in biological systems’, in Blanshard J M V and Lillford P, Food Structure and Behaviour, London,AcademicPress, 149–176. ATKINS A G andMAI Y-W (1986),‘Deformationtransitions’, J Materials Sci, 21, 1093– 1110. 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NERAAL R and HAMM R (1973), ‘ Enzymatic breakdown of added tripolyphosphateanddiphosphatein meat’, Proc 19th MeetingEuropean Meat Research Workers, 4, 1419–1427. NOBLE B J,SEIDEMAN S C, QUENZERN M andCOSTELLOW J (1985), ‘The effectof slice thickness and mixing time on the palatability and cooking characteristics of restructuredbeefsteaks’,J Food Quality, 7, 201–208. NONAKA M, TANAKA H, OKIYAMA A, MOTOKI M, ANDO H, UMEDA K andMATSURA A (1989), ‘ Polymerization of several proteins by Ca independent transglutaminase derived from micro-organisms’ , Agric Biological Chemistry, 53, 2619–2623. NUTE G R (1996),‘Assessmentby sensoryandconsumerpanelling’, in Taylor A A, RaimundoA, Severini M andSmulders F J M, MeatQuality andMeat Packaging, Utrecht, ECCEAMST, 243–255. NUTE G R, MACFIE J H and GREENHOFF K (1988),’Practical application of preference mapping’, in ThomsonD M H, Food Acceptability, London, Elsevier Applied Science,377–386. 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PURSLOWP P (1985), ‘The physical basisof meat texture: observationson the fracturebehaviourof cookedbovineM.semitendinosus’, MeatSci, 12,39– 60. PURSLOWP P,DONNELLY S M andSAVAGE A W J (1987),‘Variations in thetensile adhesivestrength due to testconfigurations’, Meat Sci, 19, 227–242. RICHARDSON R I, NORTJE G L and TAYLOR A A (1989), ‘Modified atmosphere storageof acceleratedprocessedbeef restructuredwith an algin/calcium system’,Proc 35th Int CongressMeat Sci and Tech, 5.43,918–923. SAVAGE A W J, DONNELLY S M, JOLLEY P D, PURSLOWP P and NUTE G R (1990), ‘The influence of varying degrees of adhesion as determined by mechanicaltests on the sensoryand consumeracceptance of a meat product’, Meat Sci, 28, 141–158. SCHMIDT G R and MEANS W J (1986), ‘Processfor preparing algin/calcium gel structured meat products’, US patent 4,603,054. SCHWARTZ W C and MANDIGO R W (1976), ‘Effect of salt, sodium tripoly- phosphate andstorageon restructuredpork’, J Food Sci, 41, 1266–1269. SHEARDP R andJOLLEY P D (1988),‘Restructuredandreformedmeat products’, Food TechnologyInternational Europe, 129–132. SHEARD P R andSAVAGE A W J (1998), ‘Restructuredmeatproducts in the UK: basicprinciplesandnewdevelopments’,in, JD BuckleyJ D, Honikel K O and Smulders F J M, New Meat Products Development, Utrecht, ECCEAMST, 135–149. SHEARDP R, JOLLEY P D, HALL L D andNEWMAN P B (1989),‘Technical note: the effect of temperature and raw material on the size distribution of meat particles pre-brokenby grinding’, Int J Food Sci and Tech, 24, 421–427. SHEARD P R, COUSINS A, JOLLEY P D and VOYLE C A (1990a), ‘Particle characteristics of flake-cut meat’, Food Structure, 9, 45–56. SHEARD P R, JOLLEY P D, MOUNSDON R K and HALL L D (1990b), ‘Factors influencing the particle size distribution of flaked meat I Effect of temperature,aperturesizeandpre-breaking before flaking’, Int J FoodSci and Tech, 25, 483–505. 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and receiving increasing interest in other parts of the world like Australia. The basic concept of its preparation involves comminution of muscle and fat tissue with salt, nitrate and/or nitrite and spices often including sugar, starter cultures and other additives such as non-meat proteins. After stuffing the mixture into a casing, the resulting sausage is left to ferment and dry, often in two consecutive and separate stages. The presence of salt, the lowering of water activity (aw) and the exclusion of O2 selects for salt tolerant lactic acid bacteria, producing lactic acid from carbohydrates added and/or present. This lowers pH to final values between 4.5 and 5.5, inducing denaturation of salt solubilised protein to a gel structure that can be sliced. The adequate (fast) reduction of pH and the lowered aw ensure both product stability and safety. Once these basic requirements are met, the production technology allows for many but imprecise variations, yielding a variety of different products, presenting a considerable challenge to standardisation and management of quality. The different technologies involved lead to two general types of products: • Northern type products(NP) containing beef and pork and characterized by relatively short ripening periods, up to about three weeks, involving clearly separated fermentation (about three days) and drying periods. Fermentation temperatures do not normally exceed 30ºC. Some products, particularly in the US, are not dried but pasteurised after fermentation (Pearson and Gillet, 1996). Rapid acidulation to final pH values just below 5 followed by product- dependent weight losses during drying ensures safety and shelf-life. Smoking is applied to add specific flavour (taste and aroma). 18 Quality control of fermented meat products D. Demeyer, Ghent University and L. Stahnke, Chr. Hansen A/S, Hørsholm • Mediterraneanor Southern typeproducts(MP) arepredominantly purepork products and involve longer ripening periods, up to several months. Fermentation occurs at lower temperatures ( 20ºC versus> 25ºC) and acidulation to final pH values above 5 is thereforeslower and often not clearly separated from drying. Smokeis not applied, exceptfor the typical Hungarian sausage, and shelf-life is mainly determined by drying and lowered wateractivity. Variations within these basic technologiesyield productsvarying in moisture contentbetween 25 and50%(Acton andDick, 1976).In all types,very complex and interrelated physical, chemical andbiochemical changes in the protein, fat andcarbohydrate fraction, brought aboutby meataswell asmicrobial enzyme activity, determine both safetyandsensory quality of the product (for a recent review, seeOrdóñez et al., 1999). 18.2 The quality concept As with all meatandmeat products, fermentedsausagesaresubjectto a quality concept that hasbeenenlarged, essentially becauseof the definite condition of surplus meatproduction in the industrialised countries. In the complex set of variable interacting criteria that determine purchase(consumption?)of a meat product, indirect criteria, associated with the production of meat and rarely perceptible or measurable on the product, have become more important (Demeyer,1997). Direct quality criteria are measurableon the product and mainly relate to safetyandsensoryevaluation.Thesafety of fermentedsausages is mainly determinedby the inactivation of pathogensthroughthe development of desirable added(and/orpresent)microorganismswith theassociateddecrease in pH (Lücke, 2000). It is also covered, together with indirect quality characteristics, by the traceability of the raw materialsused,as laid down in the requirements for integrated quality control (HACCP concept, brand certification; Jago et al., 2000) and receiving increasing attention from the consumer (Gellynck andVerbeke, 2001). This chapter will not deal with these aspects, but will focus on sensory quality. Indeed, whereasmicrobial and (bio)chemical changes as well as processing technology in relation to meat fermentation have been discussed extensively (seee.g. Montel et al., 1998, Ordóñez et al., 1999, Kottke et al., 1996 respectively) little quantitative and comparativeinformation is available on the factorsaffecting sensory quality and its control, exceptfor the German literature(Rödel, 1985). It shouldalsobe clear that the importance of indirect quality characteristics may increase, subject to changes in the relative importanceof the many conflicting interests associatedwith the productionof meat andmeat products (Demeyer,1997).In this respect it is worthwhile to note that the energycostof Northern type fermented sausageproduction amountsto 3.6.10 3 MJ per 100 kg final product, a value closeto tenfold higher than for 360 Meat processing othermeatproducts andmainly due to the maintenance of ripeningconditions (Stiebinget al., 1981). Within sensory quality characteristics, flavour is very important. Whereas purchaseand rejection of the product are initiated respectively by appearance (colour) and texture, flavour is the feature that convincesthe consumer to buy the product again (Verplaetse, 1994a). The typical cured meat colour is associatedwith theformation of thenitric oxideheme pigment, stabilisedby the denaturation of theglobin component(ActonandDick, 1977). In sometypesof Mediterraneanproducts, such as Spanish chorizo sausage, its importance is sharedwith that of the colour of addedchilli peppers (Fernández-Fernándezet al., 1998).Theimportanceof thecuredmeatcolour for fermentedsausagehasof coursealso beendiminished by the recentlegalisation in the EU of colouring agentssuchas Monascus red (Angkak), cochenille and betanin, derived from yeast,a scaleinsectandred beetrespectively. Methodsfor their determination have beenperfected(Brockman, 1998) and althoughtheir use may facilitate technology, it alsoallowsfor theuseof raw materials subjectto lessdemanding quality characteristics.The aptitudeof the sausage for slicing is brought about by the combination of gel formation because of acidulationof salt solubilised proteins, followed by drying. Again, the basic interaction of salt extracted muscleprotein with pH decreaseand water loss is affectedby a number of additives,including, e.g.,milk andsoy proteins,aswell aspolysaccharides. Flavour is a complex sensory reaction involving taste,smell (odour) and texture of a product. Odour or aromais by far the most importantcomponent, becauseof the high sensitivity of the nasalreceptors for the numerousvolatile components releasedduring chewing and ingestion. The number of aroma compoundsderivedfrom spicesandsmoking(Northern types) exceeds that of compounds derived from metabolism (Schmidt and Berger,1998). The latter however are considered very important for the specific sausage flavour (Stahnke,1995b). They are derivedfrom changes in the lipid, protein and, to a less extent, the carbohydrate fraction of the sausagebrought about by interaction between muscle and microbial metabolismas well as chemical reactions.Proteinsandlipids areinitially subjectto hydrolysiscatalysedby meat (muscleandadiposetissue) enzymes. This probably facilitatesfurthermicrobial (bacterial) metaboli sm of peptides, amino acids and fatty acids formed (Demeyer,2000).The relative importance of theseprocessesis closely related to the ingredientcomposition, to the rate of pH decreaseduring fermentation, andthusto processingtechnology. 18.3 Sensoryquality and its measurement Thesensoryquality of a meatproduct canbemeasuredin severalwaysby either sensory or instrumental methodsor a combination of both. All methodshave their advantages and disadvantages. Preferably, sensory quality of a dried sausageis measured by a sensory panel: a consumer panel, trainedlaboratory Quality control of fermentedmeatproducts 361 panel or an expert panel depending on the purpose in question. Sensory evaluations can be rather laborious and expensive and are therefore often replaced to variousextentsby instrumental methods, not only in development andresearchprojectsbutalso for regularquality control in thefactory.Onemust realise however, that quality profiles obtainedby merely instrumental means oftengive too simple results making it difficult or impossibleto link theprofile to the actualquality perceivedby the consumer eating the product. During the eating process,flavour is released from the product in a complex manner depending on the matrix itself and by the anatomical and physiological characteristics of the person eating the food. Also, the perceived flavour is related to the previousexperienceand presentexpectations of the individual (Rothe, 1988). The following paragraph will briefly describe the sensory methodsavailablefor measuring sensoryquality in general. Thespecific sensory and instrumental methodsapplied for dried sausageevaluationare described separately for appearance, texture and flavour together with the present knowledge on how thesequality concepts develop in relation to processing technology. Several sensory methodshavebeendevelopedandaredescribed in excellent textbooks (Piggott, 1984; Meilgaard et al., 1991). A brief survey only is presentedhere.Sensory evaluationmethodscanbedivided into differencetests, scaling andrankingtestsanddescriptivetests. In general, differencetests canbe accomplishedwith untrainedpanellists, whose numbersdependon the size of the difference,whereasdescriptive testsneeda carefully trainedpanelin order to get reasonable results (Meilgaardet al., 1991). Difference testsallow the investigatorto determine if an ingredientor processchangecausesa significant differencein the sensory perception of the product.Comparison tests (triangle, paired comparison, duo-trio, etc.) only indicate if a differenceexists or not, whereasrankingtestsalsogive information aboutthedirectionof thedifference. For estimation of the magnitude of the differenceas well, more elaborate scaling methodsand a trained panel are necessary(Meilgaard et al., 1991). However, scaling methods using hedonic category rating (e.g. like/dislike scales)are generally usedwith untrained assessors sincetrained panellists are unlikely to give trueaffectiveresponses(LandandShepherd,1984).Descriptive tests break down the overall sensoryattributesinto separate descriptors. The term ‘rancid’, for example,is oftenusedasoneof thedescriptors for evaluating the flavour of fermentedmeatproducts. During training the panelis exposedto referencesamples that represent the individual flavour or otherdescriptorsboth in orderto learnwhat they stand for andto be ableto quantify their magnitude on the sameintensity scale(Bett andGrimm, 1994). Trainedsensory panelstypically consistof five to twenty membersselected on the basisof their ability to taste andsmell andtheir availability andinterest. Af ter selection, the panellists are trained in the basic principles of sensory perception, descriptor development and flavour-intensity measurement. The training periodmayrequire manyhoursof practising to perfectevaluation skills depending on the purpose of the specificsensoryanalysis, a worthwhile effort, 362 Meat processing since the output from a well-performing sensory panel is as objective and reliable as data obtained from instrumental analysis.Over the years different formal and systemiseddescriptive procedureshavebeendeveloped. Examples are The Flavour Profile Method, The Texture Profile Method and The Quantitative Descriptive Analysis (QDA) Method(Meilgaard et al., 1991). 18.4 Appearanceand colour: measurement and development Themajor factordetermining theappearanceof a

fermentedmeat product is the colour of the product. However, visual evaluation also involves other characteristics that may be covered by the term ‘structure’, a property of significant importancein evaluationof dry sausage slices.Examplesof this are particle size, uniformity of particles, glistening of fat, stickiness and more (Meilgaard et al., 1991). Evaluation of appearance involves considerable psychophysical elements, but can be rendered objective by image analysis technology (Roudotet al., 1992).Such technology hasshown that the surface occupied by fat particles in slices cut perpendicular to the sausagelength, changes very little with drying andis about45%of thetotal surfacearea(Colas andSimatos,1976).Further discussionwill be limit ed to colour. 18.4.1 Sensorymeasurement of colour The appearance of a fermented sausage has most often been evaluated sensorially by hedonic scaling methodsor by descriptive analysis either using a point scale, a ranking scale or a continuous line scale with two anchors (Stahnkeet al., 2002;Hagenet al., 2000;Sanzet al., 1997;Diaz et al., 1997; Dellaglio et al., 1996;Næset al., 1995).Typical colour attributesfor fermented sausageare whiteness, hue, colour intensity and colour tone of fat and meat particles. In somecases,colour attributeshave beenevaluatedfollowing the Natural ColourSystem(NCS), a systembasedon theresemblanceof thesample colour to the six elementarycolours white, black, yellow, red, blue and green (ScandinavianColor Institute 2001; Stahnkeet al., 2002). 18.4.2 Instr umental measurement of colour The methodof choice for objectivemeasurementof colour is the useof CIE tristimulus values (X,Y,Z), derived from the sausagesurface reflectance of specifiedlight sourcesunderspecificconditionsandtransformedinto colour co- ordinates in order to obtain a uniform distribution. They reflect lightness, rednessandyellowness asrespectively L, a andb (Hunter,1975)or L*, a* and b* (CIE, 1976)andinterconversion betweenbothsystemsis providedfor (http:// www.colorpro.com/info/tools/convert.htm). Addi tional psychophysical parameters chromaticity, hue and redness index can be derived from the co- ordinates.Both rednessco-ordinatesarewell correlatedwith eachother andwith Quality control of fermentedmeatproducts 363 sensory colour evaluation (Ansorena et al., 1997) as well as with pigment nitrosation (Üren and Babayiğit, 1997). The sameunits can be usedfor the determinationof colour changes after exposure to light, e.g.,colour stability. 18.4.3 Colour development The formation of nitrosomyoglobin is the net result of a seriesof complicated reactions involving the formation of nitrogen oxide (NO) and its reactionwith myoglobin or metmyoglobin producing nitrosylated pigments with red and greyishcolour,respectively. In theMediterraniantypeof processing,the(added) substrate for NO productionis often nitrate, whereasin the Northern type of processing,sodiumnitrite, addedas colouring salt, is used.Use of the former involves bacterial reduction to nitrite, a process generally considered to be inhibited by pH valuesbelow 5.2 (Ally et al., 1992).The latter, however, acts uponaddition asavery reactiveoxidant,andis reducedto NO immediately after preparation of the sausage mix, associated with the oxidative formation of metmyoglobin andresulting in an immediategreyishdiscolouration of the mix, with loweringof L* anda* values(PribisandSvrzic,1995).Developmentof the stable red colour during fermentation and drying requires the subsequent reduction of the (nitrosylated)metmyoglobin back to (nitrosylated)myoglobin together with the denaturation of the pigmentglobin moiety. Theratesof boththeinitial oxidationandthesubsequentreduction, aswell as thestability of thecolour formedto lateroxidation,aredeterminedby acomplex setof factors linked to both processingandraw materials. Theseinclude, e.g., the amountsof nitrite used,the rateof pH drop during fermentation,the useof anti-oxidant additivesandtheanti-oxidantactivitiesof thestarterbacteriaused. The reducingactivity of the meatusedand/orits pH arealsoimportantfactors. In general,thesusceptibilities of (cured)meat pigmentandlipid to oxidationare tightly linked and increase with decreases of pH and of the reducing environment. Mechanisms determining the latter include, e.g., the use of oxidative muscleand thus higher pigmentand iron concentrationsand higher lipolytic activity aswell as the presenceof lower concentrations of a seriesof endogenousand/or addedantioxidative compoundssuchas-tocopherol (vit.E), numerous phenolic compoundsof plant origin and, possibly, carnosine. The interactionsof suchcompoundswith membranestructuresandenzymes,aswell aswith spicesinvolve pro-aswell asantioxidantactivitiesof e.g.nitrite andfree fatty acids(!). As pointed out recently by Bertelsen et al., (2000), much remains to be investigatedin relation to the outstandingcolour stability of Parmaham, for example where colouris formedwithout addednitrate/nitrite. It would seemthat for the Northern ripening processthe useof sodium ascorbate(e.g. 600 ppm) with minimal amountsof sodium nitrite (e.g.150ppm) is sufficient to obtain an acceptablecolour stability also reflected in a low redox potential (Ally et al., 1992), minimal lipid oxidation (Zanardi et al., 2000) and efficient oxygen consumption (Torfs andDemeyer, in preparation).The latter may be relatedto 364 Meat processing the use of starter organismswith antioxidant activities (catalase,superoxide dismutaseand/or nitrate reductase activities) also contributing to flavour development (Barrière et al., 2001).pH valuesbelow 4.9 havebeenconsidered harmful for colour development (Stiebing and Rödel, 1989). It is evident that colour control can involve the introduction of limit values for colour co- ordinates, taking into accountconsiderablevariability: Dellaglio et al., (1996) reported coefficients of variation between5 and 11% for CIELAB colour co- ordinatesfor theinterior of thesamesausagebrand,whereasTorfs andDemeyer (in preparation) could detect significant differencesboth within and between production units (cutters)in two companies. 18.5 Texture: measurement and development Threesenses– touch, sightandhearing – maybeinvolvedin sensory assessment of texture, but in the majority of cases the senseof touch plays the most importantrole (Brennan,1984)The ‘in-mouth’ textureis the parameter that is normally measuredwhenevaluatingdried sausagetextureby sensory means– eitherby descriptive analysis or by hedonicmethods. Quantification hasmostly beenaccomplishedby a point scaleor a continuous line scale(Stahnkeet al., 2002;Brunaet al., 2001; Garciaet al., 2001;Hagenet al., 2000;Mendozaet al., 2001;Patarataet al., 1997;Diaz et al., 1997).Typical texture attributesusedfor fermented sausagein descriptive analysis are: hardness, fattiness, juiciness, stickiness, tenderness,granularity, fibrousnessandclamminess. The rheologyof dry sausage is that of a viscoelastic body but its structural complexity is better reflected in empirical units, rather than in physical laws. Objective but empirical determination of food texture has been elaborated extensively, also for meat and meat products (Honikel, 1998). The force (Newton) necessary to penetrate the sausagesurfaceor interior (sausageslice) understandardised conditionsandreferredto as‘hardness’ hasbeenusedmainly for texture evaluation of dry sausage(Touraille andSalé, 1976). 18.5.1 Development of texture During comminution, the added salt solubilises muscle proteins, which coagulate and form a gel surrounding lard and meat particles upon the acidification brought aboutby fermentation.The pH necessary for coagulation increases with increasing salt concentration and is 5.3 at the often-used salt concentrationsbetween 2 and3% (TenCate, 1960).Accordingto Rödel (1985), hardnessincreasessharply when sausagepH reaches5.4 and further increases gradually until pHˆ 4.9 (Rödel, 1985).More detailedstudieshaveshownthat myosin is the major protein solubilised by salt andthat myosin filaments swell and are progressively fragmented in a ‘halolytic’ process that involves increasing loss of the typical band pattern of the myofibrils, depending on intensity of chopping and NaCl concentration. At the periphery of the Quality control of fermentedmeatproducts 365 myofibrils, swollen and partly dissolvedproteinsform a network that can be considered an ‘adhesive substance’ holding meat, connective tissue and fat particles together. This network consists of filamentous aggregates whose dimensionsandformationdependon factorssuchaspH andNaClconcentration, determining, for example, the relative rates of filament formation and aggregation(KatsarasandBudras,1992). Coagulationby acidulation or heatinginvolvesthe formation of morestable andmore intensiveaggregations, associatedwith the releaseof water. The gel formed by coagulation is further stabilised by the release of water occupying spaces between the aggregates and forms a matrix surrounding fat and connective tissueparticlesthat determines sausage texture. It hasbeenshown that proteolytic damageto the myosinmolecule, brought about,e.g.,by ageing or electrical stimulationof beefcarcasses,lowersthestrengthof heatcoagulated myosin gels (DemeyerandSamejima, 1991).Muscle cathepsinD-like activity degradessausagemyosin mainly during fermentation(Verplaetse et al., 1989, Verplaetse,1994b), but significant changes require pH< 5.1 (Molly et al., 1997). It is thereforeclear that acidulation during fermentation inducestwo opposing effectson texturedevelopment: coagulation of the myosin sol into a gel aswell asaccelerating proteolytic cleaving of myosin molecules, lowering their contribution to gel strength.A moderate negative correlation was indeed foundbetween proteolytic activity andtexture (Santamariaet al., 1994),andthe clear tenderising effect upon addition of exogenous protease to a sausagehas beenrelatedto myosindegradation(Melendoet al., 1996). Diff erent relative rates of acid induced coagulation and proteolysis may explain the positive relationship found between initial ratesof acidulationand hardnessdevelopmentasillustratedin Table18.1.Increasedratesof acidulation increase ratesof drying,a processalso determining rateof texturedevelopment. In the Northernripening process,drying during fermentationis very limited, as well as pH changeduring drying. The data in Table 18.1 show that texture developmentduring fermentation is determined by the drop in pH, irrespective of small weight changes,whereasfurther texture development during drying is then determined by the loss of water only. Both hardnessdevelopment and weight lossshowexponential changesduring ripening. However, the latter has beenreportedto deceleratewith time whereas the former accelerates(Touraille andSalé, 1976).It is clearthat numerousfactorsaffect the interrelatedratesof both acidulationanddrying. 18.5.2 Sausagecomposition and size The use of PSE pork (Townsend et al., 1980), the use of spices (Vandendriesscheet al., 1980), starter organisms (Demeyeret al., 1986) and soy protein (Stiebing, 1998) are known to increaserates of acidulation and drying andthusof texture development.Substitution of KCl andCaCl2 for NaCl at equivalent ionic strength significantly reduceshardnessas well as sensory texture andcolour intensity (Gimenoet al., 1999).A higher fat contentof the 366 Meat processing sausagemix decreasesboth rateof pH drop andrateof hardnessdevelopment (Rödel, 1985;Touraille andSalé, 1976).The useof between 50 and60%lard in the sausage mix (equivalent to 40 and 50% fat), can result in a spreadable product

(Klettner,1989).Increasing sausagediameter clearly decreasesthe rate of drying andthusrateof hardnessdevelopment (Rödel, 1985).An increasein sausagediameteralsodecreases the rateof pH decline becauseof an increasing contributionof proteolyticprocesses to metabolism (Demeyeret al., 1986)(Lois et al., 1987). 18.5.3 Conditions of batter preparation According to Rödel (1985) and Tourraille and Salé (1976), the degree of comminution doesnot affect texturedevelopment.Lowering theaveragesizeof fat particlesto 1.5mm, however was found to decreaseinitial as well as final valuesfor hardness(Table18.1); the findingsprobably related to the smearing of fat aroundprotein particles.An increaseddegreeof lipolysis for the fat used may intensify theseeffects(Touraille andSalé, 1976).In a detailedstudy under practical conditions, Van ‘t Hooft (1999) concludedthat the meanprocessing factors that significantly determine binding and structure are (i) meat temperature (ÿ2 better thanÿ4ºC), fat temperature(ÿ18 better thanÿ10ºC), saltchopping time (60 betterthan20 sec.)andvacuumtreatment(90 betterthan Table 18.1 Ratesof acidification,drying andtexturedevelopment Experiment pH % DM Hardness (Newton) Ratesof change(c)d Expt. 1: effectof startersa None ÿ0.23 0.03 0.01 Startersausage ÿ1.06 0.06 0.06 Starterorganisms(n= 4) ÿ0.580.06 0.040.01 0.030.01 Absolutechangesafter2 or 3 and21 d of ripeninge Expt. 2: effectof comminutionb Meanfat particlesize(mm2) 2ÿ3d 21d 2ÿ3d 21d 2ÿ3d 21d 24.4 ÿ0.7 ÿ0.9 ÿ1.2 9.6 64 213 3.8ÿ6.0 ÿ0.6 ÿ0.9 ÿ0.9 8.8 49 203 1.5 ÿ0.7 ÿ1.0 0.6 7.3 61 145 Expt. 3: effectof sausagediameterc % weight loss 60mm ÿ1.0 ÿ1.0 9.0 30.5 83 184 140mm ÿ1.0 ÿ1.0 4.9 17.9 87 129 a Data relate to experimentsreported by Demeyer et al., (1984). b Data relate to experimentsreportedby Verplaetseet al., (1990).c DemeyerandClaeys(unpublished). d Initial rates of change calculated from exponential kinetic models proposedby Demeyeret al., (1986).e Valuesafter ripening-start. Quality control of fermentedmeatproducts 367 0 sec.). Thelatterfactorreflectsthepresenceof air pocketsin thesausagebatter, leading to a differencebetween weight and volume loss. Salt chopping time could berelatedto extractedmyosinanda remarkablefinding wasthat,contrary to GMP, the useof blunt ratherthan sharpcutter knives is to be preferredfor goodtexture. 18.5.4 Fermentation and drying conditions Air speed,temperature and humidity not only affect rate of drying, but also result in agradientchangeof wateractivity (aw), importantfor theestablishment of productsafetyaswell asfor the developmentof texture,colour andflavour. Valuesfor aw canbeestimatedwith acceptableaccuracyfrom company-specific relationshipswith sausage compositionand ratesof drying (De Jaegeret al., 1984) or measured continuously during ripening (Stiebing and Rödel, 1992). Hardnessvaluesaresubject to variability andcoefficients of variation fluctuate between 5 and15%, valuesbeing higher for slicesthan for the whole sausage (Touraille andSalé, 1976).Nevertheless,limit s for hardnesscanbeimposedfor thefinal productandcontrolled by measurement or estimation from correlations with pH anddrying losses. 18.6 Flavour: measurementand development In general, thetermflavour is definedastheoverall impressionperceivedvia the chemical sensesfrom a product in the mouth.Defined in this manner,flavour includes thesensationof taste andaromaaswell astrigeminal feelings,suchas astringency, the pain from hot spices,metallic note from blood, etc. Texture, appearanceandthesoundsof the food duringchewing havean influenceon the perceivedflavour aswell, but theyarenot commonly included in thedefinition of flavour (Meilgaard et al., 1991). However, one must be aware that the temporal order of the sensation has a great influence on the total flavour impression,i.e., the orderof stimulation is very importantfor how the food is perceivedand liked. During eatingthe consumer is first of all confronted with theappearanceandcolourof thefood andlateron with its odour.This gives rise to certainexpectations on how the food will taste.Finally, during the chewing process, the consumer is confronted with texture, taste and aroma, which together will createthe final impression of the flavour (Rothe, 1988). The sensation of taste is caused by primarily nonvolatile compoundsin the food interacting with thetastebudson thesurfaceof thetongue aswell asin the mucosaof thepalateandareasof thethroat.Thesensation of aromais caused by volatiles in the food evaporating from the food during the chewing processand travelling throughthenasopharynxto thenasalcavity,wheretheyreact with the olfactory receptors producing an electrical signal, which is transmitted to the olfactorybulb in the front brain (Rothe, 1988).The discrepancybetweentaste andaromashouldbe kept in mind when analysingflavour eitherby sensory or 368 Meat processing instrumentalmeans.However,it is also true thatsub-thresholdconcentrationsof non-volatile compoundsmayaffectsensitivity to anaromacompound(Daltonet al., 2000). Such ‘taste-olfaction integration’ of senses is apparentfrom the aromaenhancementdueto theglutamate-umami tasteandpeptides in fermented sausagesmay havea similar effect. 18.6.1 Sensorymeasurement of aroma, taste and flavour Thearoma(or odour),tasteandflavour of driedsausageis commonly measured by hedonicmethodsor descriptive analysis,eitherusinga point scale,a ranking scaleor a continuous line scale(Mendozaet al., 2001; Hagenet al., 2000;Sanz et al., 1997; Diaz et al., 1997;Dellaglio et al., 1996).Typical tasteattributesare: acidity, saltiness, sweetness, metallicness, bitterness, umami and acidic aftertaste. Preferably tasteshouldbe measured while the panellists havea clip on their nosein orderto prevent air from travelling throughthe nasopharynx to thenasalcavity andconfusing the flavour impressionwith the tastingsensation (Bingham et al., 1990). Aroma (or odour) and flavour attributes that are frequently usedare: overall intensity, meat type (pork, beef,etc.), fresh meat, soursweet,acid, vinegar, tanginess,soursocks, spices,pepper, flowery, nutty, garlic, maturity, cured, dry sausage,butter, cheese,sourdough, fatty, rancid, nauseous, burned,solvent, smoked(Stahnke et al., 2002; Hagenet al., 2000; Stahnke et al., 1999;Zalacainet al., 1997;Viallon et al., 1996; Dellaglio et al., 1996;Stahnke, 1995c;Berdaguéet al., 1993;Acton et al., 1972). During training of panellists for dry sausageevaluation, chemical standards may be included to exemplify the qualitative description of the various attributes.This wasrecentlydoneby Erkkilä et al., (2001)who usedlactic acid, acetic acid, arginine,alanineandsalt to describe the flavour of lactic andacetic acid, bitterness, sweetnessandsaltiness,respectively. 18.6.2 Instr umental measurement of aroma and taste compounds A huge number of methods have been developedfor analysing the flavour compounds of meat productsand other foods, but one shouldrealisethat the composition of the final aroma sampleis highly reflected by the choice of method.Also, thereproducibiliy of flavour analysesis in general lower thanfor other analytical methods, in particular on complex matrices such as meat products. Standarddeviations within the samesausagerangebetween5 and more than 10% for some volatiles and between-batchvariability may exceed 50% (Schmidt and Berger, 1998, Hinrichsen and Pedersen 1995; Mateo and Zumalacárregui 1996; Meynier et al., 1999, Stahnkeet al., 2002). Flavour research hasbeenprimarily confinedto the studyof the volatile andthe semi- volatile compounds since they are the most important contributors to the characteristic flavour of most foods (Cronin, 1982).The following paragraphs will thereforefocuson themeasurementof volatile compoundsandonly slightly on the non-volatile. The basic principles include four steps:Collection of the Quality control of fermentedmeatproducts 369 flavour compounds, concentration,separationanddetection.(Bett andGrimm, 1994). Collectionof compounds Dependingon the type of flavour compounds,their polarity, volatility, etc., and the kind of matrix in which they are embedded(raw meat/cookedmeat, lipid content,structure,etc.) different collection methodsare preferredand basically, threedifferentmethodsexist; (i) directextractionwith a solvent(organicsolvent, water, super-critical fluids), (ii) distillation combined with a transfer of the volatilesinto asmallamountof solvent(e.g.,steamdistillation,Likens-Nickerson, high vacuumdistillation of extracts)and(iii) headspacecollection, in which the volatilesin theair abovethesamplearesampledandcollectedin a cold-trapor on anadsorbent(dynamicheadspacesampling),purgeandtrapsampling,solid phase micro-extraction,etc.). However,somemethodsare harsherthan othersgiving rise to extensiveartefactformationif not well suitedto theproduct.For example, steam distillation at atmosphericpressure,although claimed to induce less variability (SchmidtandBerger,1998),wouldnotbethebestchoicefor collecting aroma compoundsfrom a raw meat product, since compoundsnot originally presentin theproductwill beproducedby thermalreactionsduringthedistillation process(Parliament,1997;Wampler,1997).Althoughits usedecreasesanalytical variability, it may increasethe amountsof volatiles extractedfrom fermented sausagemore thantwentyfold comparedto headspaceanalysis(Demeyeret al., 2000). Concentration Dependingon the collection methodand the concentration of compounds, the aroma samplemayhaveto beconcentrated to a smaller volume.For extractsthe solvent is commonly evaporatedon a Vigreux columnin a thermostattedwater bath or by blow down of an inert gas,usually nitrogen, on the surfaceof the extract. In headspacemethodsusingadsorbenttrapsthearoma sampleis located in thetrap,which maybeextractedwith a minute amountof solventor desorbed by heat (seebelow). During the concentration step there is a risk of highly volatile compoundsbeing lost due to evaporation together with the solvent (Parliament, 1997;Hartmanet al., 1993;BurgardandKuznicki, 1990). Separation The separation of the flavour sample is primarily performed by gas chromatography (GC) (for volatiles) or, for non-volatiles andcompoundswith low volatility, by high pressureliquid chromatography(HPLC). The presenceof impurities or of numerouscompoundsmay necessitatepre-separation(Cronin, 1982;Merritt andRobertson,1982). Volatiles collected on adsorbent trapsare often injected directly into the GC by a thermal desorber. Aroma extractsare preferablyinjecteddirectly on-columnat aslow a temperatureaspossible since high temperatures may decompose labile compoundsand produce artefacts (Wampler,1997;Merritt andRobertson,1982).Analysis of thepeptidefraction 370 Meat processing merits special mention: early work studying proteolysis during dry sausage fermentation has usedsemi-quantitative SDSPAGE (Verplaetse et al., 1989; Verplaetse,1994b; Verplaetseet al.,1992). Sucha methodis limit edhowever to the molecular weights (MW) > 5 kD. Size exclusion chromatography (gel filtrati on) by HPLC can be usedto isolate smaller MW fractions for further analysis by reversed phaseHPLC (Lambregtset al., 1998). Detection Detection of flavour compounds in gas chromatographic analysis is mostly performedby massspectrometry (MS) andby flame ionisation detection (FID), which respondsto any compoundthat is combustible in a hydrogen flame. Element-selective detectors are available for organic

compounds containing halogens,nitrogen, sulphur and phosphorus, but are rarely used in flavour research. The advantageof the mass spectrometer compared to the other detectors is basedon its ability both to quantify andidentify the compoundsat the sametime. However, in many applications the sensitivity and the linear rangeof the MS aremuch lessthanthe otherdetectors(Rood,1999). A highly efficient,commonly useddetection principlein instrumentalflavour analysis methodis olfactometry.In gaschromatographyolfactometry(GCO)all or part of the effluent from the column is led to an outlet outsidethe GC-oven, wherea human subjectsniffs thecompoundsastheyelute.Theodoursarerated qualitatively andsometimesalso quantitatively andmake it possible to identify themore importantodorous compoundsin the food sample. While instrumental detectorsquantify the individual componentsof the food sample, thepeakareas do not necessarily correspondto the flavour intensity.Thehumannoseis much moresensitive thanthe instrumentaldetector to manyflavour compounds(Bett andGrimm, 1994).Diff erentprotocolsfor analysing flavour samplesby GCO havebeendeveloped(Blank, 1997)andmodified versionsarecommonly used (Meynier et al., 1999;Stahnke, 1995c;van Ruth andRoozen,1995). The newestprinciple for detection of volatile flavour compounds is the ‘electronic nose’,a device basedon an array of sensors eachhaving a partial specificity for eachvolatile compoundin thegasphasethusproducing anodour fingerprint that canbe identified by a patternrecognition systemwithout need for prior separation(Strike et al., 1999).Themainadvantageof electronicnoses is rapid analysis, enabling quick decisisonmaking, e.g., in relation to quality control. Electronic nosesensing was shown to be sufficiently accurateas an approximation of human olfaction apparatus, but further development is necessary althoughits successful usein discriminating between sausagetypes hasbeenreported (Vernat-Rossiet al., 1996;Eklov et al., 1998).For analysis of peptidesby reversedphaseHPLC, detection sensitivity maybea limit ing factor, necessitating the use of massspectrometry. Analogous to GCO, the liquid fractions from gel filtration or preparative HPLC on non-volatile flavour compounds may be tasted by a sensorypanel and the taste of the eluted compoundsevaluated(Henriksen andStahnke, 1997)but this approachhasnot beenmuch usedby flavour researchers. Quality control of fermentedmeatproducts 371 18.6.3 Chemical compounds related to the development of flavour Even though the flavour impressionis probably the most importantcomponent of theeatingqualityof fermentedsausage,research onthematterhasbeenrather scarce and until quite recently it was not directly focusedon the analysis of flavour compounds(seesection 18.6.2.). On the otherhandmuch researchhas beenaimedat understandingthe chemistry of cookedmeat flavour (Mottram, 1998).But oneshould becarefulnot to confuseresultsfrom meat flavourstudies with fermented sausage flavour since flavour compounds in cooked meats primarily are derived through thermal processes,whereascompoundsin raw dried meat products such as salami and dry ham mainly arise from both endogenous and microbial enzyme reactions taking place during the fermentation anddrying steps. 18.7 Taste and aroma: measurement and development The acid taste is an importantcomponentof theoverall tasteof fermentedmeat products, oftensoughtafter in theNorthernprocess,whereasit mayberejected in the Mediterraneanproduct. It is positively correlated with the D-lactate (Bucharles et al., 1984) and acetate(Demeyer, 1992) content. Only limited amounts of nitrogen-containing or protein-relatedcompoundsare found in the volatile aromacompounds(Berdaguéet al., 1993), yet, flavour evaluation of fermentedsausagehasbeenmainly related to extentof proteolysis(Demeyer, 1992),specifically in relation to surfacemould growth (Lücke, 1998). Indeed, the fatty acidspresentin sausagelipids arethemselvestoo long to beof sensory relevance. Although such findings suggestthat most of the significant aroma compoundsarederivedfrom theprotein fractionof thesausage,it is knownthat intensity of proteolysis reflects release of peptides affecting taste,rather than aroma (Nishimura et al., 1988)asshown for cheese (Fox, 1989)andraw ham (Hansen-Møller et al., 1997).Also, the non-protein nitrogen fraction will affect sausage pH (Demeyeret al., 1979) and sausage pH may affect liberation of aroma determining acid compoundsduring chewing (Dainty and Blom, 1995; Dirinck, personalcommunication). Work on proteolysis in dry sausagehas involved the initial degradation of myosin and actin (Verplaetse et al., 1992; Verplaetse,1994b;Molly et al., 1997;Harnieet al., 2000)andpreliminarywork on thepeptideandfreeaminoacid fractionhasbeenreported (Lambregtset al., 1998;Demeyer,2000). The use of antibiotics and paucibacterial meat incubations has clearly establishedthat initial proteolytic changes mainly involve myosin and actin degradationthroughtheactionof cathepsinD-like enzymes. Thecontributionof bacteria in furtherendo-and,mainly, exoproteolytic changes increasesdownto ammonia production, the end of the proteolytic chain. Mediterranean,low temperatureripening,lowers rateof pH dropandthus, cathepsinD activity and initial protein degradation as well as the proportion of smaller peptides (1ÿ10kDa). The contribution to flavour of ATP metabolites suchas IMP and 372 Meat processing hypoxanthine is also recognised and that of free higher fatty acids generally considered of less importance (Verplaetse, 1994a). Studies on the relative importance of volatiles and water solubles in flavour analysis should use multivariate statistics involving data sets for both volatile and water soluble compounds. 18.7.1 Aroma The raw sausage mince doesnot contain any volatile compoundsof sensory importance sinceit haslittle or no aroma.On theother hand,it containsa large number of aroma precursors, which during the fermentation, drying and maturation stepsareconverted by endogenousenzymes, microbial activity and chemical reactionsinto a large number of volatile compoundsof both sensory andnon-sensory importance.The first study on thearomaprofile of a fermented sausageappearedin 1990andsincethendifferentsausagesfrom all overEurope havebeenanalysedby variousanalytical methods(Bergeretal., 1990;Berdagué et al., 1993; Johansson et al., 1994; Stahnke, 1994, 1995b; Mateo and Zumalacárregui,1996;Schmidt andBerger, 1998;Stahnke et al., 1999;Viallon et al., 1996; Meynier et al., 1999;Sunesenet al., 2001;Stahnke et al., 2002). The volatiles present in fermented sausage consist of a wide variety of compounds from many different chemical classesdepending on ingredient levels, spices, meat origin, smoke, starter cultures, processing conditions, packaging conditionsetc., alkanes,alkenes,aldehydes, ketones,acids,alcohols, esters, sulphur compounds, furans, lactones,aromatics, terpenes, nitriles and more.Until now morethan200 compoundshavebeenidentified, but not all of themareof sensory relevance.In particular, compoundssuchasthealkanesand straightchainalcohols havesensorythresholdvaluesmuchtoo high for themto haveany influence on fermentedsausage flavour (Grosch,1982). By usinggaschromatography olfactometry (GCO) or multivariate statistics combining sensoryand instrumentally determined flavour profiles, it hasbeen shownthat the aromacompoundscreatingthe basiccuredsausage flavour are most likely to consistof compoundsfrom microbial degradation of fatty acids andof the aminoacidsvaline, leucine,isoleucineandmethionine together with compoundsfrom carbohydratecatabolism. More specifically, differentbranched aldehydesand acids, ketones, various sulfides, diacetyl, acetaldehyde, acetic acid andperhaps also certainethyl esters(Stahnkeet al., 2002;Stahnke 2000; Meynier et al., 1999;Stahnke et al., 1999;Stahnke 1994, 1995c;Schmidt and Berger 1998; Montel et al., 1996; Berdagué et al., 1993). Compounds originating from chemical autoxidation of lipids such as hexanal, octanal, 1-octene-3-one,etc.,areof great importance but may not be involved with the cured flavour attribute, but rather contribute to the rancid notes. Smoked sausagescontain specific top notes attributed to 2-furfurylmercaptan and guaiacol, whereas Mediterraneanmouldedsausagescontain popcorn notes due to 2-acetyl-1pyrroline(Stahnke2000).Therehavealsobeenreportsstating that degradation productsof sulphurcompounds in garlic may contribute positively Quality control of fermentedmeatproducts 373 to maturity andcured flavour (Stahnke,1998;Stahnke et al., 2002).However, flavour researchers still needto confirm thesefindings by reconstituting the proposed flavour compoundsinto a mixture holding the fermented sausage flavour. 18.7.2 The origin of the aroma compounds Figure 18.1 gives an overview of the overall enzymatic andchemical reactions that may lead to sausageflavour compoundsby degradation of carbohydrate, protein and fat in the sausagemince. Depending on sausage ingredientsand processingconditions,somereactionswill bemore pronouncedthanothers,but how thesefactors exactly determine the overall patternis not clear and much more research is neededto understand in particular, the role of starter cultures and their interactions with both the background flora and the endogenous enzymes. 18.7.3 Aroma compounds from carbohydrate catabolism During thefermentation periodmostof theaddedcarbohydrateis convertedinto lactic acid and different amounts of side productsdepending on the applied lactic acidbacteria,the typeandcontentof carbohydrate, temperatureandother processing parameters. The additional starter cultures of, for example, staphylococci or yeast probably exert some effect in converting sugarsto products otherthanlactic acid,but areof course in strongcompetition with the lactic acid bacteria. Volatile compounds in fermented sausage, generally Fig. 18.1 Simplified overviewof the primary pathwaysleadingto importantflavour compoundsin fermentedsausage. 374 Meat processing consideredto bederivedfrom carbohydratecatabolism, areacetic, propionic and butyric acids,acetaldehyde, diacetyl,acetoin, 2,3-butandiol,ethanol,acetone,2- propanol and more (Gottschalk, 1986; Demeyer, 1982; Stahnke, 1999). However, thecompoundsarederivedfrom pyruvate, which mayoriginate from manysourcesotherthancarbohydrateduringmicrobial metabolism (Demeyeret al., 1986). 18.7.4 Aroma compounds from protein degradation As mentionedearlier, extensiveproteolysistakesplace in fermented sausages creatingpeptidesandfreeaminoacids.During maturationaminoacidsandsmall peptidesaretakenup by themicroorganismsandconvertedinto numerousaroma compoundsby differentpathways(Fig. 18.1).Someof themoreimportantarethe biochemical conversions of the amino acids leucine, isoleucine, valine, methionineand phenylalanineinto the sensoryimportant branched aldehydes andcorrespondingsecondaryproducts,suchasacids, alcoholsandesters(Montel et al., 1998; Stahnke et al., 2002). The microorganisms responsiblefor those conversionsareprimarily speciesfrom the Micrococcaceaefamily. It hasbeen shown,both in modelexperimentsand in sausages,that different staphylococci andmicrococci (kocuria)produce2- and 3methylbutanal,2-methylpropanal,2- and 3-methylbutanoicacid, 2-methylpropanoic acid, 2- and 3-methylbutanol, ethyl-2- and 3-methylbutanoate,methional,phenylacetaldehyde,phenylethanol andmanymore(Berdague´ et al.,

1993;Stahnke,1994,1999;Montel et al., 1996; Massonet al., 1999; Larroutureet al., 2000). The amount of the compounds is highly influenced by the processing conditions.In minimal media, model mincesandin sausagesit hasbeenshown that parameters such as temperature, pH, glucose, salt, nitrite, nitrate and ascorbate all influencetheamount of aromacompoundsin oneway or theother (Stahnke,1995b,1999; Massonet al., 1999; Larrouture et al., 2000). Results indicate that for Staphylococcus the reactions are negatively correlated with their growth, i.e., it seems as if the organisms producemore of the above- mentioned compoundswhen they are in the resting phasethan when in active growth but this still needsto be studied further (Stahnke,1999). It has been suggested that the branched-chainedaldehydes could also arisefrom the non- enzymatic Strecker reactions between the corresponding amino acids and a diketone, suchas diacetyl (Stahnke,1995b;Barbieri et al., 1992). This would explain the presenceof different pyrazines in unspiced fermentedsausages (Stahnke,1995b; Johanssonet al., 1994; Berdagué et al., 1993). Apart from aldehydes, theStreckerdegradation results in variousketo-aminesthatdimerize into different pyrazines (Hurrell, 1982). Indeed, studieshave shown that the amount of 2and 3-methylbutanal and 2-methylpropanal was of the same magnitude in sausageswith or without microbial growth (Stahnke,1994). However, theStreckerdegradation is favouredby high temperatureandvery low water activity, i.e., conditions not prevailing in fermented sausage(Hurrell, 1982). Quality control of fermentedmeatproducts 375 18.7.5 Aroma compounds from lipid degradation During thefermentationandmaturationperiodsthe lipid fractionof thesausage mince is partly hydrolysed by lipolytic reactions in which triglycerides and phospholipids are liberating free fatty acids. Residualmono- and diglycerides havealsobeendetectedandit wasshown thatmoreunsaturated fatty acidswere liberated preferentially, probably because of a preferential membrane phospholipid degradation as well as a positional and/or fatty acid specificity of themeatlipases(Demeyeretal., 1974;Molly etal., 1997).Lipolysishasbeen extensively studied over the years since free fatty acids are believed to be important precursors for oxidation products of relevance for flavour. Nevertheless, a direct correlationbetween lipolysis and maturity development has not been established (Montel et al., 1998). Recent results indicate that methyl ketonesfrom microbial -oxidation of free fatty acidsmaybe important for maturity (Stahnkeet al., 2002)but perhapsthe amountof free fatty acidsis soplentiful that increasedamountsof this precursor do not influencetheflavour profile. Oneshouldbearin mind thataromacompoundsarepresentin theppbto ppmlevelswhereasthelevel of free fatty acidsarebetween 0.5to 7%depending on sausage type (Nagy et al., 1989; Dominguez and Zumalacárregui,1991; Stahnke, 1994;Johanssonet al., 1994;Navarro et al., 1997). Lipolysis is caused both by microbial enzymesandendogenousenzymesin the meatandfat andtherehasbeenmuchdebateaboutwhich mechanismsare the dominant. However,the most recentresultsfrom sterile model mincesand sausages with added antibiotics show that the major part of the lipolytic breakdownis attributedto endogenousenzymesevenif strongly lipolytic strains of Staphylococcus are usedas a starterculture (Molly et al., 1997; Stahnke, 1994).The pH of thesausagemincemaybedecisive for thedegreeof lipolysis arising from microorgansimssincepH is a major factor influencing the amount of Micrococcaceae, their productionof lipasesand their activity (Søndergaard andStahnke,2002; Hierro etal., 1997; SørensenandJakobsen,1996).It hasalso beenshownin sausagesthat the amountof free fatty acidsis increasedby high fermentation temperatureandreduced salt levels (Stahnke,1995a).The partial glyceridesand/or the free fatty acidsproducedduring lipolysismay oxidisevia differentpathwayschemically or microbially. It is not clear whether free fatty acids are oxidised faster than intact glycerides.Although addition of li pases increased lipid oxidationduring maturation(Ansorenaet al., 1998),otherwork hasshown that increasedlipolysis wasnot associated with increased rancidity (Nagy et al., 1989) (Fernandez andRodriguez,1991). Chemical autoxidation of unsaturatedfatty acids producesa whole rangeof volatile aldehydes, ketones,alchols, etc., some of which arevery potent aroma compounds.As mentionedabove,gaschromatographyolfactometry hasshown that compounds suchashexanal,octanaland1-octene-3-one are important for the overall flavour (Meynier et al., 1999;Schmidt andBerger, 1998;Stahnke, 1995c). In general, the influenceof autoxidation processeswill increase during maturationandstoragedepending on thesausageingredients.It hasbeenshown that ascorbate prevents autoxidation (Houbenand Krol, 1986) and that nitrate 376 Meat processing may increase it (Stahnke,1995b). Additionally, speciesbelonging to the genus Staphylococcushavebeenreported to preventautoxidation, possibly dueto their capability of forming catalaseandsuperoxide dismutasethat degradehydrogen peroxide (H2O2) andsuperoxide(O2 ÿ), respectively (Barriereet al., 2001;Talon et al., 2000). As mentionedpreviously, methylketones(2-alkanones)canbeformedduring microbial metabolism, eitherdirectly by decarboxylationof free-ketoacidsor by -oxidation of free fatty acids.Their sensorythresholdvaluesarequite high though, compared to other lipid oxidation compounds(Grosch, 1982).The 2- alkanonesmaybefurtherreducedto 2-alkanolsby alcoholdehydrogenasein the microorganism.The level of methyl ketonesincreases steadily over time in Mediterraneanfermented sausages(Sunesen et al., 2001; Croizet et al., 1992) andthePenicilliumgrowing on thesurfacemayberesponsible. However, North European nonmouldedsausagesalso containmethyl ketones,be it in slightly lower amounts (Stahnke et al., 1999). Model experiments show that both Staphylococcus and Penicillium species are capable of producing methyl ketones(Stahnke,1999;Montel et al., 1996;Larsen,1998). 18.8 The control and improvement of quality It is evidentthat themethodsdiscussed bothfor panelandinstrumental analysis canbe usedat variousstagesof the production process.The results,associated with the informationon quality developmentdiscussed above,canthenbeused to improve the progressive interactionsbetween raw materials, microorganisms andprocessing. 18.8.1 Raw materials Muscle lipaseand protease activities determine to a large extent liberation of free fatty acids,peptides,andevenaminoacidsduring dry sausage processing. Although theeffectsof animalspecieson suchchanges (Demeyeret al., 1992), as well as on flavour (Fournaud,1978) have been reported for fermented sausage,their relation to the formation of flavour compounds from fatty acid oxidation and bacterial amino acid metabolism is not clear (Demeyer, 2000). Relationshipsof muscleprotease andlipaseactivity with bothcarcassandmeat quality havehoweverbeendemonstrated(ToldráandFlores,2000;Claeyset al., 2000) and may be used for the specification of raw materials,similar to a suggestion made for raw ham production (Toldrá and Flores, 1998) and in addition to the classiccriteria relatedto pH (< 5.8), inner temperature (< 4ºC) and fatty acid unsaturation (< 12% w/w of polyunsaturated fatty acidsin total fatty acids) asdescribed,e.g.,by Stiebing (1994).Sugar(max. 2%), nitrite and nitrateadditionmay be optimised in relation to the findings discussed earlier. Quality control of fermentedmeatproducts 377 18.8.2 Starter cultures The application of starter cultures for sausage fermentation is today a natural part of industrial sausageproduction. The microorganisms used as starter culturesarecommonly divided into two groups: lactic acid bacteria, primarily responsiblefor the acidification process,andflavouring microorganisms,often capable of nitrate reduction. The first group consistsof Lactobacillus and Pediococcus, the secondgroup of Micrococcaceae(Staphylococcus,Kocuria (formerly Micrococcus)), yeasts (Debaryomyces) and moulds (Penicillium) (Jessen,1995). Lactic acid bacteriaare usedto ensure acidulationand avoid faulty production due to contamination with pathogensand other undesired microorganisms that may proliferate without the presenceof a competitive starter inoculation. Micrococcaceaespeciesand yeasts are addedto speedup and intensify flavour development and to ensure that enoughnitrate reducing microorganisms are presentin sausage minces with addednitrate. Mould is primarily usedto prevent growth of spontanousfungi capable of mycotoxin production and to shortenthe onsetof mould coverage.The choice of starters depends of courseon the type of sausage to be produced. In the fermentation processbacteria,yeastsandfungi all contributeto thefinal sensory quality of the fermentedsausage (Lücke 1998). Lactic acid bacteria The lactic acidbacteriaprimarily affect flavour formationby producing thetaste componentlactic acid of either the D(ÿ) or L(+) configuration or a mixture of both. However, undercertain processing conditionsthe bacteriamay switch to other pathways producing end products such as acetic acid, ethanol, acetoin, formate and strong-smelling sulfides (Jessen,1995).Lactic acid bacteria have beenreported to be weakly proteolytic and lipolytic and therebycapable of influencingflavour formation, but generally thesecharacteristics arenot sought for in the selection of lactic acid bacteria for fermentedsausage. Acidulation rate, lag phase, competitiveness towards endogenous flora, carbohydrate fermentation patternand optimum growth temperaturesare the typical control points. Production of hydrogen peroxideandbiogenic aminesarealsoof great concern aswell asproductionof bacteriocins,phageresistance, stability during manufacturing andmore(Jessen,1995). Micrococcaceae Several studieshaveshownthat it is possible to affect thesensory quality of the final product by changing thetypeor contentof thestarterculture.Studieshave also shownthat speciesfrom the Micrococcaceaefamily arethe major flavour contributing microorganisms (Berdagué et al., 1993; Montel et al., 1996; Stahnke et al., 2002).Model andsausageexperimentshaveshownthatdifferent strains have very different volatile profiles, which are affecteddifferently by processing parameters (Stahnke, 1995b; Sørensen and Jakobsen, 1996; Søndergaard andStahnke,2002;Stahnke,1999;Larrouture et al., 2000;Masson et al., 1999).The Micrococcaceaespeciesprimarily sold asstarter culturesare 378 Meat processing different strainsof S. xylosus,S. carnosusandKocuria varians (Jessen,1995). However, at the low pH conditionsprevailing during North European sausage production theamount of Micrococcaceaeis drastically reduced.Evenif added in highnumbersthesespeciesbeginto die outshortly afteronsetof fermentation (Johansson et al., 1994).Selection of low pH tolerant Micrococcaceaespecies for sausagefermentation is thushighly relevant. Other characteristics looked for are lipolytic and proteolytic capability, nitratereductaseandcatalaseproduction. Thelatter two activitiesareconsidered important for colour formation and colour stability and perhapsalso for preventing lipid oxidation(Jessen,1995;Talonet al., 2000).However, basedon themostrecentknowledgeaspresentedin thepreviousparagraphs,lipolytic and proteolytic activity of the starter cultures are probably not as relevant as previously suspected. In fact it may be more relevant for the culture manufacturers to look at the capability of degrading amino acids or forming methyl ketonesfrom fatty acids.Nevertheless,there is still a

long way to go beforecontrol of flavour formation in fermentedsausageby controlof growthor pre-history of Micrococcaceae is a practical reality. Most of the flavour developing pathways are not identified and their regulation on both geneand pathway level even poorer understood. Only very recently, the first staphylococcal gene for one of the enzymesin the catabolic pathway of leucine, isolucine and valine into the branched aldehydes and acids was sequenced(EMBL database, 2001). Yeast In commercialstarter culturepreparationsyeastis offeredfor both exteriorand interior use,but it is usedin much smalleramountsthan the Micrococcaceae (Jessen,1995;Andersen,2001).Debaryomyceshansenii is the dominant yeast speciesidentified in naturally fermented products and is also the species primarily soldasstarter culture (Encinaset al., 2000;Metaxopouloset al., 1996; Jessen,1995). The influence of yeast on the sensory quality of fermented sausagesis not well documented. It seemsto be highly dependent on the other microorganismspresent(Gehlenet al., 1991)andstudieshaveshownthatyeast may or may not have an influence on sausageflavour (Gehlenet al., 1991; Miteva et al., 1986;OlesenandStahnke, 2000). Due to its high oxygen demand D. hansenii is mainly observedin the periphery of the sausageswhere it stabilisescolour, degradeslactic andacetic acid and producesammonia (Geisenet al., 1992; Gehlenet al., 1991). The aroma compound production by D. hansenii has been studied in malt agar, mincesand in sausagesand it was shown that very small amountsof volatile compounds were producedcompared to other yeast species(Westall, 1998; Olesen and Stahnke, 2000). In model mincesand sausagesC. utilis is a much strongerproducerof volatiles, in particular acetates(OlesenandStahnke,2000). Both C. utilis and D. hansenii are lipolytic, but for D. hansenii the lipolytic activity is inhibited at low pH andtemperatures(Miteva et al., 1986; Sørensen, 1997).D. hansenii is a very salt tolerantspecieswith a wateractivity minimum Quality control of fermentedmeatproducts 379 for growth of 0.84in salinesolution(DeakandBeuchat,1996).However,garlic addedto the sausagemincemay preventgrowth at aw valuesashigh as0.95– 0.96 (Olesen andStahnke,2000). Fungi Mediterraneanair-dried sausagesand certain Hungarian types are fermented with mould on the surface. The mould coveragegives the final product a characteristic flavour dueto thefungaldegradation of sausageingredientsacting together with the bacterial fermentation in the inside of the sausage. Unfortunately, research on the influence of mould on sausagesis almostnon- existent andit is not clear how fungi affect flavour. A few studies haveshown, that application of different strains of Penicillium nalgiovense,Penicillium camemberti and Penicillium chrysogenum may give sensory differencesin the final product but the causeis not known (Sunesenand Stahnke, 2001). A separatestudyhasidentified a specific popcorn-smellingcompound(2-acetyl-1- pyrroline) asthemostimportantvolatile differentiating mouldandnon-moulded sausages(Stahnke,2000). On the other hand it seemsas if the other sensory differencesaredueto concentrationchanges in variouscompoundsin theoverall flavour patternratherthanto theexistenceof specificcompoundsfrom moulds. Otherstudiesindicatethatthemould mayberesponsible for muchof themethyl ketones, 4-heptanone, 1-octene-3-ol and phenylacetaldehyde in moulded sausages (Sunesen et al., 2001; Stahnke et al., 1999; Croizet et al., 1992; Kaminski et al., 1974). Moulds are lipolytic andproteolytic,perform-oxidationof free fatty acids, produceammoniaanddegradelactic acid therebyincreasingpH (Geisen,1993; Trigueroset al., 1995;Toledoet al., 1997;Lücke,1998;Larsen,1998;Selgaset al., 1999).All of theseactivitieswill affect flavour asdescribedin the previous paragraphs.Also, it hasbeenclaimed that mould coverage reducesthe risk of drying faults anddelaysrancidity by consumingoxygen(Lücke,1998),but this hasneveractuallybeenproven.However, thestrongestargumentfor usingfungal starterculturesis to preventgrowthof mycotoxin-producingfungi and to produce sausageswith aneven,white surfacewithout discolouring.This requiresthat the fungal starter has a short lag phase compared to the house-flora, high competitiveness,goodadhesivepropertiesandwhitish colourwhile still creating a final productwith thecorrectsensoryquality (Jessen, 1995; Lücke,1998).The mould primarily usedas starter is Penicillium nalgiovense, since only certain strains of this specieshave been declared non-toxinogenic (Jessen, 1995). Additionally, many Penicillia are capableof producingthe antibiotic penicillin (Andersenand Frisvad,1994). Genetechnologyis presentlybeing usedin the construction of new wellperforming andsafecultures(Geisen1993). 18.8.3 Processing conditions Customary rates of pH drop in Northern processing (4.8 after a three-day fermentation) are somewhat lower than thosereported earlier by Stiebing and 380 Meat processing Rödel (1987a, b) (about5.3 after threedays)who discussed the effect of air speed, temperature and relative humidity on the interrelated rates of drying (weight losses of 15 and 30% after 21 days for 60 and 140mm diameter sausagesrespectively), acidulation and texture development. As discussed above,developmentof colour, appearance,andflavour areaffectedby ratesof acidulation anddrying, andthusindirectly by otherprocessingvariablessuchas addition of spices (Vandendriessche et al., 1980), decontamination of spices (Bolander et al., 1995)manganese addition, degreesof comminution andsalting (Demeyer,2001).It shouldbe realisedthat the number of processing variables that may affect sensory quality is very large.As anexample, it hasbeenshown that the development of the mould-associated flavour was significantly improved by the useof natural, rather than artificial casing(Roncales et al., 1991). 18.9 Future trends in quality development Product development in the production of fermented sausages follows the generaltrendsof the food industry: acceleration of production with guaranteed sensory quality aswell assafetyandintroductionof (new) functional properties. 18.9.1 Accelerated production The useof low fermentationtemperaturesandextendeddrying periodsleadsto specif ic del icately f lavoured Mediterranean products. An accelerated fermentation at higher temperaturesand using specific starter cultures,similar to the Northernprocess,hasbeeninvestigated for Mediterraneanproducts, in orderboth to reduce thegreatersafety risks andproduction costs.However, the increasedrateof pH drop(4.8vs.5.5after threedays)interfereswith thetypical flavour development, obviously related to the inhibition of Micrococcal metabolism (Martuscelli et al., 2000)and/orthe stimulation of muscle protease activity (Molly et al., 1997).This finding hasmotivatedextensiveresearchinto the acceleration of flavour development through addition of enzymes. As recentlydiscussed,(Ordóñezet al., 1999) proteinasesandlipasescould beused to accelerateand increaseproteolysis and free fatty acid formation. However, their activity is diffi cult to control and often leads to faulty (softer) texture development. Theseauthorsstate correctly that addition of suchenzymesmay provide more substrate for flavour-producing microorganisms, but substrate concentration is obviously not a limiting factor in flavour development (Demeyer et al., 2001). Stimulatoryeffectsof cell-free preparations on aroma development (Hagenet al., 1996; Bruna et al., 2001) may be related to the presenceof non-enzymatic stimulatory agents such as manganese in the preparation used(Hagen,pers.comm.). Quality control of fermentedmeatproducts 381 18.9.2 Fermented meat products as functional foods Improvementof the nutritional value of meatproductshasbeentried for years, e.g. by replacementor lowering of fat (Arganosaet al., 1988) and salt content (Gimenoet al., 1999). More recently, the successfulenrichment with calcium (Gimenoet al., 2000) and inulin (Mendozaet al., 2001) was reportedand the concept of ‘functional foods’, e.g., foods containingnaturally, or by addition, ingredientswith clearly identified beneficialeffectson a target function of the human body and/or lowering the risk of disease(Diplock et al., 1999), were introduced into the meat industry (Jiménez-Colmeneroet al., 2001). A major target function could be the lowering of the consumerbody’s antioxidant protectionsystemthroughthe productionof meatandmeatproductscontaining natural or addedantioxidants.A well investigatedcaseis theadditionof vitamin E for improvementof colour stability, a characteristicreflecting the antioxidant statusof the meat.In freshmeat,improvement of colour stability by vitamin E was much betterwhensuppliedwith the diet, than post-mortem (Mitsumoto et al., 1993).For dry sausageproduction,these findingsshouldstimulatetheuseof raw materialswith improvedantioxidantstatusthroughselectionof animaland muscle and/ordietary treatmentsreflecting,e.g.,glutathioneperoxidaseactivity andsolubleseleniumcontent(Daunetal., 2001), conjugatedlinoleic acidcontent (Raeset al., 2001)and animalsfed dietsenrichedin polyphenols(Lopez-Boteet al., 2000;Tanget al., 2000).Otherpossibilities arereflectedin the identification of angiotensin I-converting enzyme inhibitors in the peptide fraction of fermented sausages(Arihara et al., 1999) and the introduction of probiotic startercultures(Lücke, 2000; Erkhilä et al., 2001)(Sameshimaet al., 1998). 18.10 References ACTON J C and DICK R L (1976), ‘Composition of some commercial dry sausages’, J Food Sci, 41, 971–972. 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ZALACAIN I, ZAPELENA M J,PAZ-DEPM, ASTIASARÁN I andBELLO J (1997),‘Use of lipase from Rhizomucor miehei in dry fermented sausages elaboration: microbial, chemical andsensory analysis’, Meat Sci 45, 99–105. ZANARDI E, NOVELLI E, GHIRETTI G P, DORIGONI V and CHIZZOLINI R (2000) ‘Oxidative stability of lipids andcholesterol in salameMilano, coppaand Parmaham:dietary supplementationwith vitamin E andoleic acid’, meat sci 55, 169–175. Quality control of fermentedmeatproducts 393 19.1 Introduction Analysis of raw meat quality encompasses a large variety of attributes and analytical methods. In the following section a broad definition of meat quality is presented and those attributes which are more pertinent to this discussion are highlighted. Laboratory-based methods tend to require a large input of resources. A brief overview, of some of the more popular laboratory methods is outlined in Section 19.2. There is a huge requirement for more rapid methods for the estimation of meat quality. Such methods need to be accurate, precise and suitable for use in a commercial situation. Currently, only a few earlypostmortem measurements are recorded in meat plants in attempts to obtain advance knowledge regarding quality (Section 19.3). However, a wide array of novel techniques has been tested for their usefulness as indicators of meat quality. Section 19.4 details the findings of some of these new methodologies. Animal genomics has benefited greatly from the advances that have recently been witnessed in the analysis of the human genome. Section 19.5 highlights some of the prospects this technology offers to deepen our understanding of meat quality and to the development of objective methods for analysing raw meat quality. While attempts have been made to present many of the recent advances in the area of meat quality analysis this chapter is not to be considered a definitive list of laboratory-based methods and relevant emerging technologies. 19.2 Defining meat quality Meat quality can be defined in various ways from palatability to technological aspects to safety. A common definition of quality is that it is a ‘measure of traits 19 New techniques for analysing raw meat quality A. M. Mullen, The National Food Centre, Dublin that are soughtand valuedby the consumer’. Hoffman (1990) described meat quality as the ‘sum of all quality factors of meat in terms of the sensoric, nutritive, hygienic and toxicological and technological properties.’ In the following chaptermostemphasiswill beon sensory, nutritive andtechnological aspectsof meat quality. Sensoryproperties include tenderness,flavour and colour while nutritive factors includefat, protein andconnectivetissuecontent. Technological factors include suchparametersas water holding capacity,pH, water distribution, etc. Most referenceswill be regardingbovine, porcineand ovine muscle. 19.2.1 Diff iculties for the meat industry Thevariability of meatquality preventsthemeatindustry marketing its produce according to quality. Despite muchwork in understanding thescientific basisof quality attributes(tenderness,colour, water-holding capacity, juiciness)their evaluation, prediction and control remain most elusive within the meat processing plant (i.e. within 48h post-slaughter). As a result meat produced todaycannot be guaranteed to possessthe bestquality attributesas its quality canonly be truly assessedafter purchase.Thereforethe marketability of meat, the consistencyof quality and the guaranteeingof setstandardsof product are made very difficult. The reasonsfor the variability of meat quality are numerous, but theyemanate from thefact thatthesequality attributesarealtered from postslaughterconditions,right along the production chain, into the beef processing plant, in retail outlet andevenin the purchaser’s home. 19.2.2 Why the needfor objective methods Most of the laboratory-basedmethods(seebelow) require an expenditure of time, personneland cost. Most proceduresare generally not quick enoughor adaptable enoughto an ‘on-line’ or ‘at-line’ situation. Ideally, the ultimate eating quality of meat needsto be predictedin the early postmortem period (Mullen et al., 1998aandTroy et al., 1998).By this, we meanwithin 24–48h post-slaughter, duringwhich time the carcassis within theconfinesof the meat factory. Thereis alsoa needfor a methodof assessingmeatquality at thepoint of sale.Presently,routinemethodsof measuringmeatquality, within a typical European meat processing plant, revolve arounda few measurements. These include measurementsof both pH and temperature. Commercially available probes include hand held probes for the measurement of the electrical parametersof conductivity and impedance. 19.2.3 Laboratory-based methods Many objective and subjective, laboratory-based, methodsfor characterising meat quality have been developed to aid the comprehensive assessmentof quality attributes.The whole areaof sensoryanalysisprovidesa complex array of tools for deciphering specific details relating to meat quality. The sensory New techniquesfor analysing raw meatquality 395 assessmentdepends on threeprincipalconsiderations.First thereareappearance characteristics including colour, form, size, shape, integrity, viscosity, etc. Secondare textural characteristics, which may include tenderness,firmness, mouthfeel, bite and chewability. The third principal consideration includes flavour factors suchas taste,odour, off flavours. In generalthe assessment of these sensory attributesrequires trained panelsof judgeswho can minimise subjectivity, (Singhal et al., 1997). In some circumstances, where untrained panelists are used,larger numbers of assessors may be required. A variety of sensory testsareavailable to theresearchereachprovidingquitedistincttypesof information. Analytical tests include, for example, difference test such as triangular and paired comparisons, which determineif detectable differences exist betweendifferent samples. Descriptive analysis is usedto quantitatively and qualitatively characterisesensory attributes.A

scaleusedto measure the degreeof liking or disliking is usuallycalledahedonic scale.Muchusehasbeen made in food research of this hedonic scaledevelopedby Peryam andPilgrim (1957)(seeLove, 1994for review on acceptability evaluation). A wide rangeof objective tests are available for meat quality assessment (Chrystall, 1994).Someof thephysical methodswhich havebeendevelopedto predict tenderness,asassessedby a sensorypanel,includemeasuring the force required to shear,penetrate,bite, mince,compress or stretch meat(Szczesniak, 1963; Szczesniak and Torgeson, 1965). To date, no meanswith sufficient precision havebeendevelopedor identified to predictcookedmeattenderness, with sufficient accuracy, during the early postmortem period.However, the use of the Warner-Bratzler shearforce (WBSF) blade (Warner, 1928;Bratzler and Smith, 1963) has become a standard method for estimating tenderness from cookedmeatsamples. Recently, in the US, a morerapid methodfor estimating tendernesshasbeendeveloped(Shackelford et al., 1999).Many research groups have determined the relationship betweensubjective and objective measure- ments of tendernessandin many instances‘r’ valuesof above0.7 areobserved. Instrumental analysis of flavour volatiles requires precise GC methods following extraction and concentration of the compounds. A portion of the columneffluentcanbedivertedfrom theendof thecolumn,prior to thedetector and routed through a port to be sniffed by a human subject for qualitative evaluation. Splitting the effluent in this manner with the use of a sniffer port allows for simultaneoushumanevaluation and instrumental qualification. The useof mass spectrometrygreatlyenhancesthis analysis.Other instruments such as high performance liquid chromatography (HPLC) are also usedfor flavour analysis. Themeasurementof thewater-holdingcapacity(WHC) of meat is carriedout in many differentways(seeHonikel andHamm1994,for review). All measure theinherentability of thecellular andsubcellular structuresof meatto hold on to part of its own and/oraddedwater. In spite of the variation in methodsused, there are three main treatments that give rise to three basic procedures for measuringWHC, i.e. (i) applyingno force, (ii) applying mechanical force and (iii ) applying thermalforce. 396 Meat processing Colour is usually consideredthemostimportantsensory characteristic in the appearanceof meat. Various systems exist for the objective measurementof colour with CIE L* a*b* or Hunter Lab being quite popular (seeMacDougall, 1994for review). In thepastmeat wasoftendescribedin a simplistic mannerasa combination of muscle fat and moisture and small amounts of non-combustible material (ash). However, with new labeling laws, growing interest and focus on the nutritional value of food meatcompositional analysis encompassesmanyother attributes (Elli s, 1994). In recent years,in particular, there has beena lot of interestin the analysis of fatty acids.Because of their reported health benefits the ratio of unsaturated to saturatedfats,andthe level of individual fatty acids suchasconjugatedlinoleic acidhavereceived a lot of attention. GC andHPLC arecommonly usedmethodsin the analysis of fatty acids. 19.3 Current state of art techniques 19.3.1 pH A knowledge of pH and its importancein the quality of meat is an essential element in meat quality measurements. Postmortemglycolysis results in the accumulationof lactic acidandadeclinein thepH of themuscle from about7.2, at death,to roughly 5.5 after rigor mortis onset(Geesink,1993).In pork, rapid pH declinecanresultin pale,soft, exudative (PSE)meat,which presents a large problem to pork producers. To date the most effective predictor of the occurrence of this condition is the measurement of the early postmortem pH decline. In pork pH measurements at 45min postmortem (pH45) are usedto detectthepresenceof PSEconditions(Somerset al., 1985).Recently Kircheim et al. (2001) showed pH45 displayed a high degreeof reliability in correctly predicting PSE and RFN (reddish-pink, firm, non-exudative) meat while Eikelenboom et al. (1996) suggest ultimate pH is a good predictor of pork tenderness.In bovinemuscle, measurementsat 48h postmortem(pH48) areused to detectDFD meat.While Shackelford et al. (1999)reported that pH3 wasnot an effective predictorof meat tenderness,O’Halloran et al. (1997) concluded that both the early postmortem and ultimate pH of muscle, has an important effect on the disruptionof myofibrillar proteins and thus on meat tenderness. The relationship betweenpH and temperature up to 24h postmortem is an important factor when considering ultimate meat quality. Recentresearch has focusedon themannerin which eventhe temperatureof themeatat the time of samplingwill influencethe pH (Jansen,2001; Bruce et al., 2001). In general glass or solid state electrodesare used to measure pH electrochemically. Investigations at The National Food Centre(NFC) have recently shown that significant variation in recorded pH values is introducedthrough the use of different types of meters and probes.For industrial situations a solid state electrode would be the most suitable,however, some diffi culties have been notedin terms of drift within the probe, which may be associatedwith protein New techniquesfor analysing raw meatquality 397 build up. Andersen et al. (1999) suggested that near infared(NIR) and visual rangespectrometric methodsare comparableto the precisionof the standard glass electrodepH meter. 19.3.2 Electrical impedanceand conductivity The electricalconductivity of musclechangeswhen damageto differing degrees occurs to the membrane systemof the muscle during postmortem glycolysis. Conductivity is a way of testing the intact cell membraneswithin a muscle tissue. Impedance,which is a combination of both resistanceand capacitance, decreaseswhen thereis a disruptionin membraneintegrity (Kleibel et al., 1983) andan increasein fluids within the muscletissue(Pliquett et al., 1995).Early postmortemmeasurementsof theseelectrical parametershave beenacquired from trials within the NFC and have been compared with sensory and technological attributes in pork. Pearson correlationsrevealed that impedance andconductivity measurementswere significantly correlatedto the colour,drip loss and tenderness values. Schoeberlein et al. (1999) ascertained that impedancemeasurementsact asa good indicatorof pork quality, while Lee et al. (2000) suggestthat conductivity (24h postmortem) may be a reliable predictor of waterholding capacity in pork. The relationshipbetween electrical impedanceandbeeftendernesshasbeenexploredby Lepetitet al. (2002).Using anarbitrary methodof segregatingbovine carcasseson thebasisof colour,drip loss and pH, a strongercorrelation (rˆ 0.84) betweenconductivity 24h, and WBSF 14 dayswasobserved(Mullen et al., 2000) in oneclassificationgroup. Some relationship exists between electrical measurements and tenderness, however, it would appear that this is not a simple, linear relationship. The usefulnessof conductivity and impedance measurementsas quality predictors hasbeenaddressed by manyresearchersandmore detailsregardingimpedance, can be read in Chapter10 in this book and a paperby Pliquett and Pliquett (1998). 19.3.3 Colour Colour measurementsin the early postmortemperiodhavebeeninvestigatedfor their relationship with meat tenderness. Jeremiah et al. (1991) conclude segregation(tenderness)basedon both pH and colour appearto offer little in advantageover the use of pH alone. While more recent studies suggesta relationship between colour and tenderness(Wulf et al., 1997), correlation coefficientswere quite low (rˆ ÿ0.38 (WBSF); rˆ0.37 (sensorytenderness)). Wulf and Page (2000) suggestedinclusion of muscle colour and pH would increasethe accuracyand precisionof the USDA quality gradingstandardsfor beefcarcasses.A monochromaticfiber-opticprobewasdevelopedby MacDougall and Jones(1975) to measurethe internal reflectanceof meat. It has a peak sensitivity at 900nm, where absorbanceby red heme pigments is minimal (Swatland,1995).Theusefulnessof the fiber-optic probein segregatingPSEand 398 Meat processing DFD classeshasbeendemonstrated(MacDougallandJones,1980;Garridoet al., 1995).However,this probehasnot beentakenup by the industry to any great extent.Following analysison a large numberof topsidepork muscles,we have shownbothreflectance,usinga handheld,noninvasiveprobe,(Optostar)andthe CIE L* valueof colour, performedwell asobjectivemethodsof segregatingthe visualquality of pork topsidesprior to processinginto hams(NFCresultsaccepted for ICoMST 2002). Tan et al. (2000) concludedthat a colour machinevision systemwasanaccuratemethodof evaluatingpork colourwhile vanOeckelet al., (1999) found double density light transmissionto be a useful method.Results from a multichannel fibre optic probe indicate that adiposeand collagenous connectivetissuehavehigh reflectancevalues(Swatland,2000). 19.4 Emerging technologies In recentyears,newtechnologies havebeendevelopedwhich showpromisefor exploitation and use in the meat plant. These include both physical and biochemical techniques,which aredescribed in more detail below aswell asin otherchapters in this book. Theseshowpotential for useasindicators of meat quality andpavethe way for further research into their predictive ability. 19.4.1 Ultra sound Soundwaves with frequencies abovethe audible rangeare called ultrasound waves.A number of variablescharacterising the propagation of an ultrasound signal, through a medium such as meat, can be measured. In addition the ultrasound measurements canalsobe madeat a numberof frequencies. Sound movesby compressionwaves,whicharereflected andrefractedwhentheymove from one medium to the next. Sono-elastography is a method which uses ultrasonic pulsesto track the internal displacementsof small tissueelementsin responseto externally applied stress. The mechanical properties of meat have beencharacterisedby two sono- elastography parameters – the propagation velocity and the attenuation co- efficient of the mechanical wave. Optimisationof the measurementconditions have taken temperature,sample dimensions, probedimensions and frequency rangeinto account. Measurementstaken from beefsampleshaveindicatedthe usefulnessof this technologyasa nonintrusivemethodof visualisingstructural characteristicsof beef (Ophir et al., 1993; and Crossand Belk, 1994). These investigationsindicatedthatmeasurementsmaydescribe musclestructureat the musclebundlelevel. The evolution of meat during rigor onsetandageingwas followed by pH measurementsandmechanical resistance of myofibrils at 20% of deformation. Comparisons were made between theseparametersand the variables from the sono-elastography analysis. Results indicate that sono- elastographycanbeusedto follow rigor mortisonsetandageing in meat.Elastic deformation of intramuscularconnective andadiposetissuecausedby external New techniquesfor analysing raw meatquality 399 stressis detectedultrasonically andhasbeenproposedasa methodof predicting beefquality (Swatland, 2001). Abouelkaram,etal., (2000)haveanalysedbovine muscle samples and investigatedthe influence of compositional and textural characteristics on ultrasonicmeasurements. The methodusedwasbasedon the measurement of acoustic parameters(velocity, attenuation andbackscattering). They concludethat the ultrasonic methodusedis robust enoughto

havereal potential for muscletissuecharacterisation. A novel ultrasound techniquehas been developedwith the potential to rapidly andaccurately measure tendernesson small samples of meat (Allen et al., 2001).This technique hasmuch higher resolution than previously applied methodsand is, therefore,very sensitiveto meat texture. The methodis also sensitive to differences in meat composition,particularly fat andprotein content. It is possible, therefore, that composition and texture could be measured simultaneously to give an overall picture of the likely eatingquality of meat. This could be particularly useful in processed meatswhere it is important to know thecompositionandtextural propertiesof intermediateemulsionsin order to control the eating quality of the final product. Anisotropy of ultrasonic velocity is capable of tracking structural changesin ageing beef and has potential as an indicator of eating quality in beef (Dwyer et al., 2001a,b). However, further work on a broaderspectrum of meat samplesis needed to validate this approachfor predicting beefeating quality. 19.4.2 Nuclear magnetic resonance (NMR) NMR imaging measures energy differences between magnetic momentsof naturally occurring, intrinsically magnetic atoms, when external fields are imposed.The relationship between waterdynamics andmuscle typeshasbeen exploredusingNMR. Various quantitative NMR parameterswhich areclosely relatedto waterdynamics, namelyrelaxation curves (T21 andT22) andmagnetic transfer parameters,havebeenacquired andanalysed. According to Beauvallet andRenou(1992), NMR hasprovento bea powerful techniquefor thestudyof transformations in muscle tissue and is of value in assessing meat quality. Further measurements, recorded at 3h and 14 days postmortem in bovine muscle, detected a redistribution of water over the ageing process.This redistribution is being analysedto monitor its suitability in determining meat quality (water holding capacity). A patternwas seento exist for someof the NMR measurementsversus time postmortem for different pH falls. This was thought to bepartly dueto pH fall andpartly dueto muscle shortening. A study by Brondrumet al. (2000) concludedNMR to be a better predictor of water holding capacity,intramuscular fat and total water content, than the useof a fibre optic probeor visible or NIR spectroscopy.Laurent et al. (2000)published a good overview of the characterisation of muscle by NMR imaging and spectroscopic techniques. These techniques give non-invasive access to stuctural, metabolic and chemical information as well as water dynamics and fat distribution. However, the costof this analysismay be prohibitive. 400 Meat processing 19.4.3 Image analysis Imageanalysisof meathasbeeninvestigatedwith theview to identifying features which are characteristicof the meatsample.Textural attributesof photographic imageswere analysedusing severalfeatureextractionmethodsto evaluatethe possibility of identifying bovine muscle (Bassetet al., 2000). This involved acquiringphotographicimagesof meatsamplesunderbothultravioletandvisible light. Classificationsexperimentswere performedto identify the bovine muscle accordingto muscletype,ageandbreed.Classificationof musclesfrom animals within oneagecategoryled to high identificationrates,while classificationsbased on ageof the animalandbreedsprovedmoredifficult. 19.4.4 Autofluorescence(AF) spectroscopy AF wasassessedfor its potential to predictthe fat andconnective tissuecontent in meat (Wold, et al., 1999b). Meat samples containing varying amounts of meat, fat and connective tissue were analysed. The results conclude that at different wavelengthsalong the spectra, AF may provide a rapid methodfor detection of connective tissue(380nm) and fat (332nm) contentin meat. AF spectroscopyhasalsobeeninvestigatedin conjunctionwith imagingto analyse postmortem changesin sensoric tendernessand WBSF measurements. An optimum excitation wavelength has been demonstrated for modeling the biochemical constituents. Good correlationshave beenobtained between the emission spectra and time postmortem. Combining spectral data with information from imagescan result in betterprediction modelsfor fat content (Wold, et al., 1999a). 19.4.5 Near Infar ed (NIR) spectroscopy Applications of NIR for the prediction of functional properties and quality variables in foods have emerged. NIR spectrometry is both rapid and nondestructive and can be calibratedto measureseveral componentsat one time. Infrared light is partof thebroadspectrum of energy knownaselectromagnetic radiation. NIR spectrometry is concernedwith a specificregionof the infrared, adjacent to the red end of the visible spectrum. The frequency of wave oscillations in the IR region is of the same order as the natural mechanical vibrational frequencies of many chemical groups(Benson, 1993).The types of absorptionsthat dominateNIR arehydrogenic absorptionssuchasÿOH,ÿNH andÿCH vibrations.Thesetypesof absorptionsaredisplayedby moistureand virtually all othermajor constituents of foodstuffs. Many applications of NIR havedealtwith the quantitative determination of compositional analysis of foods(Osborn andFearn, 1986).NIR spectrareflect the organic constituents of food products and contain information about the conformation of components such as proteins and polysaccharides. NIR applications have also focusedon direct estimation of quality parameters in foods. WhenusingNIR spectrato predictthefat content it is advisableto mince New techniquesfor analysing raw meatquality 401 or grind the meat into a homogenousmixture (Isaksson et al., 1992; Rodbotten et al., 2000). In this way a single NIR scanwill probably detect the ‘true’ composition.Perhapsincreasingthenumberof NIR scanssubstantially on intact meat samplesmayimprovetheprediction results for fat (Rodbotten etal., 2000). The ability of NIR to detectchanges in the stateof waterandhydrogenbond interactionsin foodshasbeenobserved (Hildrum et al., 1995). Sincesuchchanges evidently occur in meat during tenderisation and ageing it was thought that a relationship may exist betweenNIR measurementsand meat quality attributes. This wasinitially investigatedby Mitsumota et al. (1991)who observeda strong relationship between NIR and both WBSF and compositional measurementsof meat. Sincethenmanystudiesconcluded that NIR wasa goodpredictorof meat tendernessasassessedby WBSF(Byrne,1998;Parket al., 1998).However, these prediction modelswere not always easily replicated (NFC, unpublished work). Recently work at the NFC (Venel et al., 2001) focusedon avoidanceof a number of potential experimental errors which may have mitigated against the developmentof satisfactory models.While NIR (750ÿ1100nm) was unable to satisfactori ly predict the selected organoleptic properties of bovine M. semimembranosus (SM), better results were obtainedfor the WBSF values in the LD (rˆ 0.51). While the predictive performance was improved, when the samplesetwassegregatedaccording to animal grade, sex,ultimate pH or day of boneout (rˆ 0.54ÿ0.72), the accuracieswereno betterthanpreviouslyreported (NFC, unpublishedwork). NIR spectra(1100ÿ2500nm) werecollectedpre-rigor in bovine M. longissimusdorsi (LD) (Rodbottenet al., 2000).While thesespectra hadhigher overall absorbanciescomparedto post-rigor measurementsthe results did not supportthatearlypostmortemNIR spectracouldbeusedasa predictorof beef tenderness. 19.4.6 Temperature It is well known thattemperatureplaysa majorrole in determining meat quality. Problemssuchascold shortening, heatrigor andcold autolysisareassociated with postmortem carcass temperature. May et al. (1992) concluded that an internal longissimusdorsi temperature(4.5cm to 5.5cm into themedial portion immediately anterior to the 9th rib) of 33ºCat 2.5h postmortemwasrelated to the tendernessof the meat(rˆ ÿ0.63 (WBSF); rˆ 0.54 (sensorytenderness)). Pork loins having low carcasstemperatureat 3 h postmortem havehigher pH and water holding capacity and produced lower lightnessand WBSF values (Park et al., 2001). Optimal beef tendernessafter ageing for 14 days was associatedwith anintermediatepH declineof pH5.9ÿ6.2at 1.5h postmortem or rigor temperatureof 29ÿ30ºCat pH 6.0(HwangandThompson,2001).In lamb a temperatureof approximately 15ºCat onsetof rigor appearsto beoptimal for tenderness(Geesinket al., 2000). Not all researchers however agreeto the usefulness of temperature in the identification of differences in tenderness (Jones and Tatum, 1994). Perhaps strategic temperature measurementsmay provide useful information on the ultimateeating quality of meat. 402 Meat processing 19.4.7 Immunoassays The application of immunoassay technology to the analysisof non-clinical samples in theFoodandAgricultural sectorshasbeengrowing steadily for some time (Rittenburg and Grothaus,1992). It is a powerful analytical tool that dependson theinteraction betweenanantibodyandtheantigenbeing measured. It canprovide a rapid,economical, highly sensitive andspecificanalysisandis relatively simpleto perform. In comparisonto other analytical methodssuchas electrophoresis and high performance liquid chromatography (HPLC), immunoassays allow a higher sample throughput with minimal sample processing. This analytical method has been used in the detection of food contaminants such as antibiotics, pesticides and microbiological organisms (Rittenburg, 1990).The potentialof this methodfor investigating endogenous food componentssuchas vitamins, enzymesand structural proteins hasbeen realised(Finglas et al, 1992;Doumit et al, 1996). Proteolytic degradation of key myofibrillar proteins has been shown to contribute to post mortem tenderisation(Troy et al., 1987; O’Halloran 1996; Boyer-Berri and Greaser, 1998). Degradation of many structurally important myofibrillar proteins,during thepostmortemageing of meat,hasbeenobserved by many researchgroupsincluding NFC. Of thesetroponin T and its 30kDa myofibrillar proteolytic fragmenthavebeenrelatedto meattenderness(Buts et al., 1986;Troy et al., 1987). It hasbeensuggested that the appearance of this 30kDa fragment could serve as an early postmortem indicator of meat tenderness. A soluble 1734.8Da fragment of the troponin T molecule has recentlybeenisolated(Stoeva et al., 2000;Mullen et al., 1998b;Nakai et al., 1995)which appears to berelatedto meat tenderness(Mullen et al., 2000).Due to its solubility this fragment is more easily extractedfrom meat than the myofibrillar 30kDa and, therefore, it may be a more suitable candidate for routine factory analysis. An immuno-based assay was developed using polyclonal antibodies for the detection of this fragment.Initial resultsshow a relationship between formation of the fragment and beef tenderness.The calpastatin/calpain proteolytic system which has been implicated in the tenderisation process has also been targeted for the development of an immunoassaytest (Doumit et al., 1996; Koohmaraie, 1996b). Exoprotease activities can constitute a novel and adequate technique to predict early postmortempork meat quality (ToldraandFlores,2000).Theseenzymesremain stableup to 24h postmortem. Development of immuno-basedassays to these andother importantenzymesandproteolytic fragmentsareunderway with the ultimate aim of predicting meat quality traits. The analytical performanceof theseassaysneedsto bethoroughly validatedandconvenient samplepreparation proceduresdesignedfor applicationof theassays to meat extracts.Evaluationof the efficacy of the assays in the prediction of meat tendernessis alsonecessary and the resulting data can then be usedto select the assay or combination of assayswhich give the best correlation with

alternative indices of tenderness. Data collected from the validation stages would also indicate whether a qualitative or quantitative assayformat is neededfor a final test system.There New techniquesfor analysing raw meatquality 403 are somereservations aboutspeedof immunoassays for use in a commercial situation (Koohmaraie, 1996b). However, ultimately, and more ideally, a successfulassay could be developedinto a morerapid test suchasa ‘dip-stick’ type test, which would be morereadily transferableto the meatindustry. 19.4.8 Metabolites Many metabolites exist in muscle,bloodandurinewhich may contain valuable information regarding the variability of quality between different animals. Determinationof someof thesefactors may be part of routineanalysis in some laboratories. Results from thesesamples may provide an indicator of meat quality and may also provide a greater knowledgeof the biochemical process occurring over this period(Troy et al., 1998).Higherlevelsof metabolites such ascreatinine phosphokinase,free fatty acidsandhydroxybutyratehavebeen linked to the ultimate pH (pHu). No relationshipwasobservedbetween various bloodbiochemicalparametersandpHu (NFC, unpublishedresults).Nucleosides and nucleotides also play an important role in the biochemicalchanges which occur during the early postmortem period. There is a rapid decreasein high energy molecules such as tri- (ATP) and di- (ADP) nucleotides, early postmortem, with a simultaneousincreasein mononucleotides (AMP, IMP, GMP, etc.), and nucleosides (adenosine, inosine, guanosine, etc.). Levels of hypoxanthineandinosinewere different in exudative andnormal pork meat up to 3 dayspostmortem (Battle, et al., 2001).In thesamestudy IMP andATP only differedbetween 4 and6h postmortemwith the IMP:ATP ratio differing up to 2h postmortem. The authorssuggest that 2h is the optimumtime for sampling when attempting to predictPSE.In anotherstudy the sameauthorssuggestthat nucleotidecontentsmayserveasanindex of some tastevariationsbetween pork quality classesbut a direct link may be unlikely dueto their rapid metabolism and the low degreeof differences accounted for (Flores et al., 1999). Other novel metabolites of interest include nitric oxide (NO) which is a gaseous intercellular messenger and has recently been proposed in ubiquitous roles, including thosewithin a normal functioning skeletal muscle.WBSF valuesfor striploins incubatedwith NO enhancers were seento decreasewhile thoseof striploinsincubatedwith NO inhibitorsincreasedat days3 and6 of conditioning (Cook et al., 1997). The mechanismof NO in tenderisation is not yet known, however NO can mediate its effects by free radicalsand/or calcium changes which canin turn affect proteolytic enzymes. The non-enzymatic tenderisation of meat proposed by Takahashi (Takahashi 1996) and involving calcium ions could be partially explained by NO. 19.4.9 Tenderness probe As mentioned aboveefforts have beenmadeto developphysical methodsto predict tenderness,as assessedby a sensory panel. As well as the Warner- Bratzler shearforce method,otherinstrumentshavebeendevelopedandtested. 404 Meat processing The MIRINZ (Meat Industry ResearchInstitute of New Zealand)tenderness probeconsists of two sets of pinson which meat samplesareimpaled(Jeremiah andPhillips, 2000). Tension is appliedto the musclefibres by onesetof pins which rotaterelative to a staticsetof pins. A torquesignal is recordedagainst the angleof rotation. Resultsindicate it may be an alternative methodto the WarnerBratlzer.However, this methodwould still require cookingof themeat. Ideally the industry requiresa methodwhich would allow measurementsto be takenon raw meat,eitheron the carcassor on primal or retail cuts. 19.5 The geneticsof meat quality In recent yearsgreat advances have beenmade which have enableddeeper understandingof the relationship between genomics and meat quality. It is anticipated that breeding programmes will be greatly improved through identificationof polymorphismsin theDNA sequenceswhich impacton quality traits. Functional genomics aims to provide further insight to the complex interplay of geneexpressioneventsinvolvedin thedevelopmentof meatquality. Theimportanceof thisexpandingareaof researchis becoming moreapparentin the understandingof meatquality (Mullen et al., 2000andmany referencesin the following paragraph). The readeris also directedto Marshall (1999) and Solomonet al. (2000)for further informationin this area. Complementaryto the functionalgenomics approachis proteomeanalysis(Andersonet al., 2000).The useof proteomics allows the characterisationof expressedprotein within any given cell type.This is a very powerful techniqueasthe phenotypic traits of an organism areultimately manifestedthroughthe interaction of the environment andthevariousproteinsexpressed in its tissues(structural, enzymatic,metabolic andregulatory proteins) (Pandey andMann, 2000). DNA markers, (regions of chromosomesshowing polymorphisms in the nucleic acid sequence)can be usedto detectquantitative trait loci (QTL), or regionson a chromosomewhich havea substantial effect on quantitative traits suchastenderness,growth rate,intramuscular fat etc. This is referredto asQTL mapping. To successfully carry out QTL analysis, several hundredanimalsare required. Thesemust be producedover severalgenerations using pure bred animalsand employing strict control of the breeding regimes. DNA markers linked to theQTL canbeusedto develop strategiesfor markerassistedselection (MAS) breedingprogrammes(for review readDentine, 1999).Preliminarydata from genome-wide scanningof DNA markers have revealed a number of putativeQTL associated with meat traits, althoughrelatively few results have beenpublished to date.Therehavebeenseveralprojects,world wide, designed to identify QTL affecting phenotypessuchas meat quality, carcassattributes, growthanddevelopment of beefcattleandpigs. The following aresomeof the research groups that are currently undergoing programmesin this area: Jay Hetzel and Bill Barendse’s group from the CSIRO in Australia (Hetzel and Davis,1997andHetzel et al., 1997),YoshikazySugimoto from the Shirakawa New techniquesfor analysing raw meatquality 405 Instituteof Animal Geneticsin Japan,SteveKappes’groupat theUSDA MARC in the US (Stone et al., 1999),animalgenomicsgroupat TexasA&M (Taylor and Davis, 1997, 1998), animal genetics group in Michigan StateUniversity, and Michel George’s group from Belgium. Casaset al., (2000) hasidentified suggestive QTL for longissimus muscle area,hot carcassweight, marbling and WBSF. QTL for carcassandgrowth traits havebeenidentified (Stoneet al., 1999). The chromosomal locations of at least five genesinfluencing beef tenderness and another four genesinfluencing marbling havebeenidentified (Taylor and Davis, 1998andHetzel et al., 1997).A QTL influencing WBSF hasalsobeen recently identified (Keeleet al., 1999).In pork QTL for IMF andbackfathave been identified (for review seeDe Vries et al., 2000; Rothschild, 1997). In general, however, relatively little hasbeenpublished concerning thelocalisation of genesinfluencing variations in beefcattle phenotypes. 19.5.1 Major genesand candidate genes Although many quantitative traits seemto be controlled by multiple genes, individual genescanaccountfor a relatively largeamountof variation in some traits. Thesegenesare referredto as major genes. Candidate genesare genes which arerelatedphysiologically or biochemically to the selectedtrait andare assumed to have an effect on trait performance. Using this approach several majorgeneshavebeendetected.Recentevidencesuggests thatdoublemuscling in some beef breedsis caused by a mutation of a gene located on bovine chromosome 2 that produces the protein myostatin (Grobet et al., 1997; Kambadur et al., 1997; Smith et al., 1997). Normally, myostatin serves to repressskeletalmusclegrowth, but themutation appearsto block this effectand permits extra muscle growth. Porcine stresssyndrome(PSS) or malignant hypothermia (MH) is a geneticdisorderthat canresult in suddendeath or PSE meat in domestic pigs.Initially thegeneticmutationresponsible for this disorder waslocated to theMH locus but subsequentwork demonstrateda mutationin a single (major) gene, the ryanodine receptor gene (see DeVries et al., 2000; Cunningham, 1999for review). An exampleof acandidategenefor meatquality is providedby thegenefor fatty acid bindingprotein(FABP).Polymorphismsin this gene(heart andadipocyte)havebeenfoundto be associatedwith variations in IMF in pigs (Gerbenset al., 1998a,b). In addition, the effect appears to be independent of backfat. Anotherrelevantcandidateapproachis theresearchon calpainandcalpastatin.Therearemanyreportsof therole of thecalpain system, a setof calcium dependentproteasesandtheir inhibitor calpastatin,both in vivo and postmortem in protein turnover and meat tenderness(Koohmaraie 1992, 1996a;Zamoraet al., 1996).Threepolymorphic siteshavebeenidentifiedin the pig calpastatingene(Ernstet al., 1998).Significant associations between beef tendernessand calpastatin genotype were detected by Greenet al. (1996a,b), but not by Lonerganet al. (1995). 406 Meat processing 19.5.2 Geneexpression and microar ray technology Genomics is the study of an organism’s whole genetic blueprint and the variations within that blueprint which make every individual in a population unique. Functional genomics seeksto relate differences in the genetic blueprint to physiology andphenotype. It is widely believedthat thousandsof genesand their products(proteins)in a given living organism,function in a complicated and orchestrated way to create the unique characteristics in individuals. Differencesin geneexpressionor changesin the sequence of expressed genes contribute to the various phenotypesin any animal population. Traditional methodsallow only onegeneto be studied at a time. However, thereis much excitementat presentover theuseof microarraysor biochips,andtheir potential contribution to the study of genomics.The technique, which involves laying down an orderedarray of genetic elements onto a solid substrate, is useful becauseit enablesgeneticanalysisof thousandsof genesandmarkersin asingle experiment (Zhaoet al., 1995;Dugganet al., 1999;Sinclair,1999). Combining microarraytechnology with methodsof molecularbiology allowscomparisonof gene expression to be made betweenindividuals or between cell types etc. (Yang et al., 1999;Liang andPardee, 1992).Using this technologywill allow patterns of gene expression to be compared between animals displaying extremesof quality traits of interest.In this mannera ‘favourable’ setof gene expression patterns may be definedfor particular quality traits. Thesepatterns could be monitoredthroughvarious treatmentregimesto determine an optimal setof conditionsthat shouldexist within the animalprior to processing.Many research groupsworld wide, includingNFC,havedynamic programmesin place to determine the relationship betweenpatterns of geneexpression(andprotein expression) and meatquality traits. This is an exciting and revolutionary area with much potential for real applications to improving the consistencyof the quality of meat. While methodology requiresinvestment in termsof time and development of specific tools, the benefits in the medium to long term are potentially great. 19.6 The future Many innovative advances have been made in the area of measuringand predicting meatquality traits. It canbeseenthat in manycases the findings can be difficult to interpret and may be contradictory to others.Obviously factors such as experimental design, sampling methodology, sampling conditions,

instrumenttypeanddataanalysisarecritical to the interpretationof results.The application of any of thesetechniquesto an online situation will requirelarge scale industrial basedtrials to verify and confirm their ultimate usefulness. Many advanceshave been made in the area of DNA and gene expression analysis. It is anticipatedthat this will contributegreatlyto our understanding of meatquality traits. It is possible thatearlypostmortemprediction of meatquality will require recording more than one ‘on-line’ measurement. Ultimately New techniquesfor analysing raw meatquality 407 predicting meatquality attributesmay requirea more holistic approach which sets criteria at morethatonepoint alongthechainof animalproduction through to consumption. 19.7 Sourcesof further information and advice A wide arrayof booksareavailablefor general readingon the sciencebehind meat quality attributesandtheir measurements.A few of the morenoteworthy include Singhal et al. (1997), Pearsonand Dutson (1994), Kress-Rogers and Brimelow (2001), Taylor et al. (1996) and Lawrie (1998). Throughout this chapter many referenceshavebeencited,many of which arereview articlesor book chapters, rather than list all of thesehereagain the reader shouldconsult the relevant sections. In the areaof meat quality prediction (especially using various probes) Chapter 10 in this book should be read, in conjunction with many of the published papersby this author. Someof the resultsdiscussed in this chapterarefrom research carriedout undertheEU FAIR programme(Fifth Framework), projectnumber PL96-1107andvariousnationally funded projects (Departmentof Agriculture, Food andRural Development,Ireland). 19.8 References ABOUELKARAM, S., SUCHORSKE, K., BUQUET, B., BERGE, P., CULIOLI, J., DELACHARTRE, P. and BASSET, O. (2000) Effects of bovine muscle composition and structureon ultrasonic measurements.Food Chemistry, 69 (4), 447–455. 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(1999b) Quantificationof connective tissue(hydroxyproline) in groundbeefby autofluorescencespectroscopy. Journal of Food Science, 64 (3), 377–383. WULF, D.M. andPAGE,J.K. (2000)Usingmeasurementsof muscle colour,pH and electrical impedanceto augment thecurrentUSDA beefquality standards and improve the accuracy and precision of sorting carcasses into palatability groups.Journal of Animal Science, 78, 2595–2607. WULF, D. M., S. F. O’CONNOR, J. D. TATUM andG. C. SMITH. 1997.Using objective measurementsof muscle color to predict beef longissimus tenderness. Journal of Animal Science, 75, 684–692. YANG, G.P., ROSS, D.T., KUANG, W.W., BROWN, P.O. and WEIGEL, R.J. (1999) Combining SSH and cDNA microarrays for rapid identification of differentially expressedgenes.Nucleic AcidsResearch, 27, 1517–23. ZAMORA, F., DEBITON, E., LEPETIT, J., LEBERT, A., DRANSFIELD, E. AND Ouali, A. (1996) Predicting variabi l i ty of ageing and toughness in beef M.Longissimusdorsi et thoracis. Meat Sci. 43, 321–333. ZHAO, N., HASHIDA, H., TAKAHASHI, N., MISUMI, Y AND Sakaki, Y. (1995) High- densitycDNA filt er analysis: a novelapproachfor largescalequantitative analysis of geneexpression. Gene, 156, 207–213. 416 Meat processing 20.1 Introduction Meat packaging technology has evolved rapidly over the past two decades yet despite major developments in packaging materials and systems the fundamental principles of packaging muscle foods remain the same. Packaging fresh meat is carried out to delay spoilage, permit some enzymatic activity to improve tenderness, reduce weight loss, and, where applicable, to ensure an oxymyoglobin or cherry red colour in red meats at retail or customer level (Brody, 1997). When considering processed meat products, factors such as dehydration, lipid oxidation, discolouration and loss of aroma must be taken into account (Mondry, 1996). Many meat packaging systems currently exist, each with different attributes and applications. These systems range from overwrap packaging for short-term chilled storage and retail display to 100% carbon dioxide atmosphere packaging for long-term chilled storage (Payneet al., 1998). Considerable interest has developed recently within the retail sector in merchandising centrally processed, display-ready, meat cuts. Packs are prepared at the meat plant and from here, placed straight onto the supermarket shelves in this form. The notion of centralised fresh meat packaging began almost immediately after the corner butcher had moved to the backroom of the newly emerged supermarket in the 1950s (Brody, 2000). The meat and retailing industry’s movement towards centralised packaging and distribution has led to an increased interest in other types of packaging systems which may have potential use for the future. The only criterion customers have at the point of purchase of fresh meat cuts is visual appearance (Kropf, 1980). Consequently, desirable colour must be maintained during chilled 20 Meat packaging H. M. Walsh and J. P. Kerry, University College Cork storage, distribution and subsequent retail display if preservative packaging systemsare to be effective (Jeremiah andGibson,1997). A longer shelf life is also required for long- and short-distance distribution. The use of modified atmosphere packaging (MAP) as well as vacuumpackagingsystems are just some of the optionsavailableto the processor/retailer.The shift from point-of- saleprocessingto central processinghasalsoled to theintroductionof motheror master packaging systems.Thesesystemsconsistof a numberof gas-permeable overwrapped trays, sealed in a master pack which contains a modified atmosphere. Thesemay be superior to MAP, provided that the meat maintains anacceptable appearance for a sufficient periodafterbulk packsareopenedand individual meattrays aredisplayed. In conclusion,selecting a preservative packagingthat is appropriate for a particular fresh/processedmeat product for a particular niche market requires knowledge of the principal deteriorative processes to which the product is subjected,thegeneral hygieniccondition of theproductwhenit is presentedfor packaging and the temperature history that the product can be expected to experienceduring its storageanddistribution (Gill, 1991) The dominant preferenceamong consumers in their daily food consumption patterns (after tasteandsafety)is for convenience.Consumerswant their food fast andeasy(Kinsey,1997).The family unit hasdecreasedin sizeover recent years andmore peoplearenow living alone. Therearenow morewomenin the workforce, who do not desire complicated food preparation each evening. Longer commuting to and from work and increasingly busy life-styles also contribute to the needfor convenience.Therefore, smaller servings of a wide choice of meat cuts, well presented in packs in retail display units are the obvious choice for consumers. Centralisedmeatpackaging offers a number of significant advantages to the industry andthe consumer. For the industry, the overall costsof production are reduced. Transportation costs are lower and trimming, evaporation and drip losses are reduced also.There is also improvedinventory and product control with theuseof computerisedproduct movementsystems.This leadsto accurate forecastingof requiredstock andcanall becarried out from onecentrallocation (www.packstrat.com).Centralprocessingalso offers someeconomyof labour for theindustry. Personnelwork onahigh-speed,automatedline, eachwith their ownspecifiedjob, andgreater safetyis achieveddueto closesupervision.At the very least, retailers must be knowledgeable about the differences between packaging treatmentsto make cost effective buying decisions, which in turn, will benefit the consumer (Schulter et al., 1994). The advantages for the consumerinclude better sanitation and enhanced palatability due to controlled ageing of the product (www.ansci.uiuc.edu/ meatscience/Library/packaging.htm). The choice of product available to the consumer has also improved. Fifteen to twenty years ago, only fresh poultry meat wasseenin shelf-readypackaging. However,today a wide rangeof fresh andprocessedpork, lamb andbeefproducts, arealso available. Therefore, the main contributors to fresh meat deterioration leading to loss of profit, are, 418 Meat processing colour, microbiology and drip loss. Processedmeats on the other hand,need protection from bacteriological contamination, oxidation, dehydration, discolouration and lossof aromato ensurea goodquality product is available to the consumer(Mondry, 1996). Before considering the form of packaging which will be usedto pack muscle food products, it is important that factors which will determine shelf-life quality of a particular meat product are considered, measuredand quantified wherepossible.For the purposes of this review,meatquality factors will be divided into those for freshmeat andthose for processed meatproducts. 20.2 Factors influencing the quality of fresh and processed meat products The principal factors that mustbeaddressedin the preservation of freshchilled meataretheretentionof anattractive, freshappearancefor theproduct which is displayed anda delayin bacterial spoilage (Gill, 1996).Minimising drip losses is also of economicconcern because such lossescan increase the cost of the product, which is often traded on narrow profit margins. During storage, processed meats deteriorate in the first instance because of discolouration, secondly becauseof oxidative rancidity of fat and thirdly on account of microbial changes (PearsonandTauber,1984). 20.2.1 Meat colour In the mind of the averageconsumeraboutto purchasemeat,colour becomes synonymouswith freshredmeatquality (RenerreandLabas,1987).Thecolour of fresh red meatis of the utmostimportance in marketing sinceit is the first quality attributeseenby the consumer who usesit asan indication of freshness and wholesomeness.The colour of fresh meat is not well correlated with the eatingquality howevertheconsumerstill demandsthatbeefhasa bright cherry red colour (Taylor, 1996), lamb a brick red colour and pork and chicken a uniform pink colour. Meat colour depends on myoglobin,a pigmentwith severalforms (Renerre andLabas,1987) (seeFig. 20.1).Myoglobin is concernedwith the storageand transfer of oxygen within the muscle. Myoglobin concentrationsare variable between speciesandbetween muscles.Light chickenmeat, porkandbeefcontain 0.01, 1–3 and 3– 6mg/g myoglobin, respectively (Warriss, 1996). Deoxy- myoglobin or reduced myoglobin is purple in colour and is the predominant musclecolour in the absenceof oxygen. It is the expected musclecolour of vacuumpackagedmeat.Whenoxygenis introducedor whenmeatis exposed to air, deoxymyoglobinbecomesoxygenated to oxymyoglobin which is responsible for the bright cherry red colour consumers expect to seeon the supermarket shelves.If oxygenis removed, oxymyoglobin reverts to the basicdark purple myoglobin pigment(Taylor,1996).Overaperiodof time andunderatmospheric Meat packaging 419 conditions,whichmayvary from severalhoursto several days,oxymyoglobin is furtheroxidisedto metmyoglobin.This is thepigmentresponsible for thebrown discolourationassociated with non-saleable meat (Kerry et al., 2000). Deoxy- myoglobin andoxymyoglobin arehemeproteinsin which the iron is presentin the ferrousstate(Fe2+)while metmyoglobin possessesthe ferric (Fe3+)form. Theconversionof theferrousto theferric form is brought aboutby oxygenation. Myoglobin canrapidly combinewith or loseoxygenin responseto thepartial pressureof oxygento whichit is exposed(LivingstonandBrown,1981).Ledward (1970) found that the formationof metmyoglobinon bovine M. semitendinosus wasmaximalatapartialO2 pressureof 6mmHg at0ºC.Meatcanbemaintainedin muchhigheror extremelylow O2 concentrationsin orderto avoid thesecolour- destructive O2 tensions. Sorheimet al. (1995) reportedthat pork loin sections stored in CO2 atmosphereswith 1.0, 2.8 and 4.0% O2 for 12 days were all discolouredbut thatsectionsstoredin O2 freeCO2 werenot. Greeneet al. (1971) reported that 40%metmyoglobincausedmeatrejectionby consumers. The pigment of curedmeats, nitrosylmyoglobin, is stablein the absenceof oxygenor undervacuumbutoxidation to metmyoglobin is rapidwhenoxygenis present.Therateof oxidation increasesdirectly with increasing oxygentension. Low humidity and high storage temperature may result in a brown discolouration on the surface due to chemical alteration and dehydration. Nitrosylmyoglobin is much

more susceptible to light than myoglobin; cured meats canfadein onehour underretail display lighting conditions.Sincelight acceleratesoxidative changes in the presenceof oxygen,vacuumor inert gas packaging will help reduce the effect (Robertson, 1993). Lundquist (1987) discoveredthatholdingvacuumpackagedmeatsin thedarkfor 1–2 daysbefore exposing themto display lights allowedresidualsurfaceoxygento be depleted by microorganismsand tissueactivity, thus reducingcolour deterioration. He also reportedthat to inhibit colourchangesin curedmeatproducts,a lower level of available oxygen than that required to shift the microbial population from aerobic to anaerobic wasrequired. Fig. 20.1 The colour of freshred meatrelatedto the forms of the pigmentmyoglobin (SorheimandNissen,2000). 420 Meat processing Thedegree of photooxidation of thenitrosyl meatpigmentis highly affected by theoxygenpressureabovethecuredmeat productbut it canbeminimisedby the use of low oxygen transmission rate films in combination with vacuum packaging or packaging in modified atmospheres without oxygenor interactive packaging with oxygenabsorbers (Andersenet al., 1988, 1990). 20.2.2 Lipid oxidation Lipid oxidation is a leadingcauseof quality deterioration in muscle foods(Rhee et al., 1996),resultingin rancidity, off-fl avoursandoff-odours aswell ascolour and texture deterioration (Kanneret al., 1992). Lipid oxidation in vivo and in musclefoods,is believed to be initi ated,in the highly unsaturatedphospholipid fraction in subcellular membranes (Morrissey et al., 2000). Immediately preslaughter,andduring the early postslaughter phase,oxidation in the highly unsaturatedphospholipid fraction is no longer highly controlled andthebalance between the proxidative factors and antioxidative capacity is likely to favour oxidation. At this stage it is unlikely that thedefensivemechanisms thatexist in the live animalstill function (Morrisseyet al., 1998). Mechanical boning, mincing, restructuring andcooking cancausesignificant disruption of the cellular compartmentalisation structure which facilitates the meetingof proxidantswith unsaturated fatty acidsresulting in thegenerationof free radicalsand propagation of the oxidative reaction(Buckley et al., 1995). Themajorproductsof lipid oxidationarethehydroperoxides, which breakdown into secondaryproductssuchasaldehydes, alcohols, hydrocarbonsandketones. Thesesecondaryproductsformedduring oxidationcontribute to theoff-flavours generated during storage(St Angelo and Spanier, 1993). A distinctive off- flavour developsrapidly in meat that has beenprecooked,chilled-stored and reheated. The term Warmed-OverFlavour(WOF) hasbeenadoptedto identify this flavour deterioration. Autoxidation of membranephospholipids is largely accepted as causal in the formation of WOF. It is thought that the polyunsaturatedfatty acids from polar phospholipids rather than triglycerides areresponsiblefor the initial developmentof off-fl avoursandoff-odours in raw andcookedmeats(Renerre andLadabie, 1993). Lipid oxidation is not usually a limiting factor in conventionalover-wrapped traysasair-permeablefilms allow odourvolatilesto escapethroughthe package. However,with modified atmospherepackages,the volatile productsareretained within thepackageandcanbeclearlydetectedby consumerswhenopened(Zhaoet al., 1994).Theseodourscan be termedas compartmentalisedpackagingodours andmay arisethrougha complexinteractionof productvolatileswith packaging volatiles in a manipulatedgaseousenvironment.Storageof meat in high O2 atmospheresleadsto a limited shelflife dueto lipid oxidation.Taylor etal. (1990) reportedthat malonaldehydein beef samplesincreasedin modified atmosphere packsmore rapidly than in vacuum packsbut not until one week after retail packaging.Jacksonetal. (1992)foundthatbeefstriploinspackagedin 80%O2 and 20%CO2 at 3ºC developedstrongoffflavoursasa resultof lipid oxidation. Meat packaging 421 Cookedor pressuretreatedmeatsaremore vulnerableto oxidationthanfresh meats.Factorswhich influencetherateandcourseof oxidation of lipids arewell known and include light, local oxygen concentration, high temperatures, presenceof catalystsandwateractivity. Control of thesefactorscansignificantly reduce the extent of li pid oxidation in foods. St Angelo and Spanier(1993) discoveredthat heme-containing catalystssuchasmyoglobin, hemoglobin and cytochromesmayalso causeoxidation. Nitrites,which areaddedto meat during curing, are thought to prevent lipid oxidation or the formation of meatflavour deterioration. It hasbeenwell documented that vacuumpackaging or modified atmospherepackagingin ananoxicgashasbeenshownto reducelipid oxidation of precookedmeatseffectively (Nolanet al., 1989;Spanieret al., 1992). Even though precooked meatsare placed in an anoxic environment, lipid oxidation still proceedsdueto residual oxygenin the product andthe package. The residual concentration of oxygenin MAP packagesis normally 0.5–2.0% (Smiddy et al., 2002,Randall et al., 1995).Bertelsenet al. (2000)statedthat the oxidative stability may be further improvedif a raw material with an optimum intrinsic oxidative stability, achieved by feeding supranutritional levels of vitamin E, is usedfor production of theseproducts. The combined synergistic effects of supplementing animals with dietary -tocopheryl acetateand the subsequent manipulation of packagingsystems to improve meat quality and extend shelf-life of muscle food productshave beenshown by a numberof researchers. Cannonet al. (1995)showedthat packagingat low oxygenlevels combinedwith dietary vitamin E washighly effective in decreasing TBARS in chill-storedprecookedporkchopsandroasts.Kerry etal. (1996)reportedthat- tocopherylactetatesupplementedmodifiedatmospherepackagedbeefincreased colour stability in steakcoreswhen compared to aerobically packaged cores. O’Gradyet al. (2001) found that lipid andoxymyoglobin oxidation in minced beef stored in 80% O2 : 20% CO2 were lower in muscle from vitamin E supplemented animals compared with unsupplementedanimals. 20.2.3 Meat microbiology The microbial population of freshmeatis affectedby a number of factors such as species, health and handling of the live animal, slaughtering practices, chill ing of thecarcass, sanitation during fabrication,typeof packaging usedand handling throughdistribution andstorage(Young et al., 1988).Most microbial contamination of muscle tissueoccurs after the animal has beenslaughtered through two main sources, those derived from the slaughter environmentand organismsfrom theintestinaltract. Thepredominantorganismson thesurfaceof freshly prepared carcasses are gram-negativebacteriasuch as Acinetobacter, Aeromonas, Pseudomonas and Moraxella. Enterobacter and Escherichia are also found. Gram-positive organismsare less abundant but commonly include Brochothrix, other lactic acid bacteriaandMicrococcaceae. The wrapping materials for fresh over-wrapped meat are only slightly permeableto watervapourbut highly permeable to oxygenandcarbondioxide. 422 Meat processing Therefore, conditions for microbial growth are favourable. The predominant organisms in this caseare the aerobicpsychrotrophs,such as Pseudomonas, Acinetobacter and Psychrobacter spp. Pseudomonads in particular causea putrid spoilage of the meat. Vacuum packaging and using high oxygen impermeablefilms caninhibit thegrowth of Pseudomonasbut it doesnot affect thegrowth of Lactobacillusorganisms,which arefacultativeanaerobesandtend to thrive in vacuum-packagedmeats. Lactic acid bacteriahavetwo particular advantages. Firstly, they developat a slower rate than aerobic gram-negative flora, resulting in a longershelf life. Secondly, the sour‘off’ odour,which can be detectedon opening of packs,is far lessoffensivethanputrid odours. Thereare inconsistenciesin the literaturerelating to the growth of different bacterialstrains in vacuumpackaged meat. Newton and Rigg (1979) reported that these contradictions could be explained if films of different permeabiliti es were used in eachstudy. High oxygen modified atmosphere packagedmeat spoils aerobically with the spoilage flora being dominatedby Pseudomonas. Their growth rate is only half that attained under nonpreservative aerobic conditions. Low oxygen modified atmosphere packaged meat is normally spoiledby lactic acidbacteriaif theatmosphereusedis 100%CO2. Thegrowth rateof the lactic acidbacteria is nearly halveddueto thebacteriostatic effectof CO2, resulting in a longer shelf life than obtained for equivalent vacuum packagedproducts. Many factorsinfluencethenatureof themicroflora thatdevelopin processed meatproductsduring chill storage.Themainfactorsarenitrite concentration,salt concentration(which affectstheaw), presenceof oxygenandpermeabilityof the packagingfilm. Theoverall pH of theproductmayalsoplay a part (Zeuthenand Mead,1996).Themostfrequentlyobservedtypesof bacterialspoilagein vacuum packed,sliced,cooked,curedmeatsareasweet/sourodourcausedby lactobacilli, leuconostocsand streptococci(Mol et al., 1971); a cheesy odour caused by Brochothrix thermosphacta (Egan et al., 1980); a sulphide odour causedby Enterobacteriaceae and greening caused by hydrogen peroxide producing lactobacilli. Boeremaet al. (1993) reported that the advantage of shelf-life extension afforded fresh meats by carbon dioxide controlled atmosphere packaging,over that attainablein vacuumpackaging,doesnot apply for sliced cookedham. The presenceof yeastsand moulds can be a problem for some processedmeat products,especiallyon dry meat surfaces. The most common speciesof yeastsencounteredon meatproductsare Candidaand Rhodotorula. The presenceof mould growth on packagedmeat is usually an indication of a defectivepackagingsystem.Yeastscancausespoilagewhencounts areaslow as 105/g meat,whereas,bacterialspoilagedoesnot usually occurbelowpopulations of 107/g–108/g meat.McDanieletal. (1984)reportedthatvacuumpackedcooked beefsteakswereorganoleptically acceptableafter 21 daysstorageat 4ºC,while modifiedatmospherepackagedsteakswerenot fit for consumptionafter14 days of storage.Hintlian and Hotchkiss(1987)foundthathighCO2 MAP waseffective in inhibiting the growth of Pseudomonas fragi, Salmonella typhimurium, StaphylococcusaureusandClostridiumperfringeson cooked, slicedroastbeef. Meat packaging 423 20.2.4 Drip loss One of the main quality attributesof fresh meat is its water-holdingcapacity becauseit influencesconsumeracceptanceand the final weight of the product (Den Hertog-Meischke,1997). The loss of exudatesfrom muscle tissue is unavoidable.Any systemprolongingtheshelf life of packedchilled meatwill be subjectto accumulationof exudatesor drip. Thedrip is thoughtto originatefrom the spacesbetweenthe fibre bundlesandthe perimysialnetworkand the spaces betweenthe fibresandtheendomysialnetwork(Offer andCousins,1992).These spacesappearduring rigor development.Factors that may affect drip losses includerigor temperatureandmembraneintegrity (Honikel, 1988;Honikel et al. 1986),preslaughterstress,processingfactors,andpackaging(Payneet al., 1997). Exudatelossesareexacerbatedby cuttingof meatinto smallerportions.Lossesof approximately5% of the primal cut weight at the packingplant canbe expected. The amountof drip in cut meat is also largely dependenton samplethickness, surfaceto volumeratio,orientationof cut surfacewith respectto musclefibre axis andprevalenceof largeblood vessels(Farouket al., 1990). Taylor et al. (1990) found that drip losses were lower for vacuum skin packaged samples than modified atmosphere packaged samples. Payneet al. (1998)

investigateddrip loss in beef under conventional vacuum packaging systems and non-vacuumpackaging systems and found that drip loss can be reduced by using a packagingsystemthat avoids applying a vacuum. The accumulation of juice from processedmeat products is alsoa causefor concern in vacuumpacks.Vacuum skin packsagainhavethe advantageover vacuum packsfor processed meats in that thereis no excess of film aroundthe product, leaving virtually no space for product juice to collect (Mondry, 1996). Condensation of moisture on the surfaceof the meatand the package may be preventedby carrying out packaging operationsin anenvironmenthaving a dew point temperature below the subject temperature (Rizvi, 1981). Antifog properties in fresh meatpackagingfilm are provided by lowering the surface tension of the film through incorporating a wetting agent into the film formulation or by coating the surfacewith a wetting agent. 20.3 Vacuum packaging Todaythemostwidely usedmethodemployed to extendthestoragelife of fresh meat is vacuumpackaging (Bell andGarout, 1994).In theUSA, 97%of all beef is estimated to have been fabricated and transported as a vacuumpackaged product (Humphreys, 1996). Vacuum packaging extendsthe storagelife of chilled meatsby maintaining an oxygendeficient environmentwithin the pack. The air within the packagemust be evacuated effectively to nominal anoxic levels (lessthan500ppm)to preventirreversible browning dueto low levelsof residual oxygen.The exclusion of oxygen from the meat surfaceas soon as possible after the breaking of the carcassinto primals preserves the meat’s potential to reoxygenatefollowing retail packdisplay. 424 Meat processing The conceptof ‘boxed beef’ wasdevelopedby French Scientistsasearly as 1932, to prolong the shelf-life of frozen meatstoredas milit ary provisions. It wasnot until 1966,however, thatbeefwascentrally processedanddistributedin this form. Todaydifferentpackaging materials areusedbut theconcept remains the same.The carcassesaredivided into parts,deboned and trimmed, vacuum packed in heavy plastic bags, placed in corrugated paperboard boxes and shipped to retailers. Boxed beef is a preferred method of packaging by distributors andretailers becauseweight lossanddrying canbe prevented,it is hygienic, meat colour and quality are maintained as films of low O2 permeability are used,operationscan be centralised, rational distribution is possible andthereis easeof inventorycontrol (Tomioka, 1990). The preservativeeffect of vacuumpackagingis achievedby maintaining an oxygendepletedatmospheresincepotentspoilagebacteriaareinhibitedin normalpH meatunderoptimumvacuumpackagedconditions(Gill, 1991).Themicroenviron- mentwithin thepackwill determinethetypeof microflorawhich develops (Devore and Solberg, 1974). When meat is first vacuum packagedany residual oxygen remainingin thepackis consumedby meatandmusclepigments(HoodandMead, 1993)andCO2 is producedasthe endproductof tissueandmicrobial respiration. Underagoodvacuumthepackageheadspaceconsistsof < 1%O2 and10–20%CO2 (Lambertet al., 1991).This typeof packageseverelyrestrictsthegrowthof aerobic microorganismssuch asPseudomonasandfavoursfacultativeanaerobic organisms such as Lactobacillus (desirable)and Brochothrix thermosphacta(undesirable). Theseareslowgrowing bacteria,theycauselessoffensivetypesof spoilageathigher bacterialnumbersthanotheraerobicorganismsandwill eventuallycausespoilagebut onlyaftermanyweeksof storage(Muller, 1990).Underaerobicconditionsthegrowth of Brochothrixthermosphactaat chill temperaturesis inhibited at pH valuesbelow 5.8.However,thegrowth of thisorganismis oftenassociatedwith theearlyspoilage of vacuumpackagedhigh pH meat. If vacuumpackaging procedures are followed correctly, the storagelife of meatcanbe extended(Muller, 1990).Caremust be takento ensurethe initial bacterialload hasbeenkept as low aspossible by adherenceto good hygiene procedures. The temperature must be maintained as near as 0ºC as possible (Brody, 1989). High pH andDFD meat mustalso be avoidedasearly spoilage may occur (Humphreys, 1996). The success of packaging is thought also to dependlargelyuponthedegreeof vacuumisation achieved. High vacuumlevels resultin themostdesirable musclecolourandfat appearance.Vacuumpackaged meatof normal pH (< 5.8) can be storedfor 12 (Eustace, 1989) to 14 weeks (Hood andMead, 1993)at 0ºC. Vacuum packaging is a simple easily controlled processwith any failure clearly identified by visibleair pocketsremaining in thepack.Thereis increased hygieneandsimplified handlingduringdistribution andstorageaswell asmore efficient use of refrigerated storage. There is more efficient processcontrol throughthe useof flow line techniqueswith subsequentincreased productivity. Thereis also a significant reduction in skilled labour and wasteat retail level associated with vacuumpackaging (Humphreys,1996). Meat packaging 425 However, vacuumpackaging is consideredunsuitablefor redmeatsfor retail display purposessincetheoxygendepletedatmospherecauses themeat in these packages to be the purplish colour of deoxymyoglobin and therefore not acceptableto consumers (Gill, 1991).Semanet al. (1988)observedthatvacuum packagedmeathadgreater colour stability thanmeatstoredin carbon dioxide. Pork chopsstoredin vacuumwerealso more desirable in appearanceandhad more acceptablecolour thanaerobically storedchops(Doherty andAllen, 1998; Doherty etal., 1996). Therangeof productsto whichstraightvacuumpackaging can be appliedis limit ed however; vacuumpackagingis ineffective for whole carcassesor cuts of shapes which prevent the packaging film being closely applied to all surfaces(Gill, 1996). Theformationof drip in meatpackagingis unsightly,andrepresentsaportion of theproductthat theconsumercannotuse.Many studiesreported thatvacuum packagedmeatproducedhigher levels of drip thanmeatpackagedin modified atmospheres (Doherty et al., 1996, Schulter et al., 1994, O’Keefe and Hood, 1982).However, a very low level of drip is observedwhen meatis shrink-wrap vacuumpackaged.This lower drip losscouldbedueto thefact that thereis less spacefor drip to form, or dueto softerpackaging or a combination both (Payne et al., 1998).Vacuumpackaging is consideredunsuitablefor meatproducts that aresensitive to pressure,for example very thin slicesof hamthat whenpacked undervacuumarediffi cult to separate without damage.Theintroduction of CO2 or N2 flush at this stagecould prevent slice adhesionandprovide bettercolour retention dueto the removalof residual O2. Vacuumpackagesfor meatareformedin four basic ways.Thefirst methodis through heat shrinking a flexible packagingmaterial around the primal cuts (Zagory, 1997).Shrink bagsaresupplied pre-madewith asealprovidedat either endandalong thesides.Whentheyarebriefly exposed to heat,abuilt in tension, called ‘locked in tension’ is released and they shrink in both directions. This process increases film thickness, improving mechanicalresistance and oxygen barrier properties. The level of drip is alsoreducedandhandlingof the product is improved. Most of theseshrink bagsare made from multi-ply formulations basedon polyolefin resins,with eitherpolyvinylidenechloride(PVDC) or ethyl vinyl alcohol (EVOH) asthe gasbarrier component(Humphreys, 1996). The second methodis by using a preformedplastic bag, also known as a pouch,in anevacuationchamber(Zagory, 1997).Thebasicpouchstructureuses polyamide (PA) asthe outer layer which providesbarrierandphysicalstrength properties with an inner core and sealing layer of polyethylene(PE) or li near low density polyethylene (LLDPE). Thesematerials cannotbe shrunk which may give rise to the accumulation of drip in the creasesandfolds (Humphreys, 1996). The third methodis the useof thermoforming traysin line from a baseweb (Zagory, 1997).After theproduct hasbeenplacedinto thenewlyformed tray, a second film web,coming from a secondreel of film is placedon the top of the tray. The resulting pack is evacuatedin this caseandthe top andbottom films aresealedin themachine’svacuum-sealingstation. After cuttingthesealedweb 426 Meat processing acrossand longitudinally, finished single packs leave the machine (Mondry, 1996). The final methodis throughvacuumskin packaging, in which the product actsasa forming mould (Zagory, 1997).In vacuumskin packaging the meat is placedin a rigid pre-formedtrayor on theflat surfaceof a flexible basematerial. The top web is first softened by heatand air is evacuated.The top web then forms closely around the product, shrinking as it does, and forms a seal everywhere it comesinto contact with the base(Humphreys,1996). A numberof packaging systems exist for processed meatsalso. Vacuum packaging is usedfor thickly slicedmeats andwholepiecesof processed meats. Vacuumpackagingwith a steamshrinkoperation canalsobeused.This method removesloose film and wrinkles are reduced. The product must be able to withstand the heattreatment during shrinking. Vacuum packsfrom rigid trays are used for stackedslices of processedmeat. The shapeof the product is designedto fit tightly to the package dimensions. Modified atmospherepacks from flexible film are usedfor salamis,bulk packsof sliced meatsand bulk packsof frankfurter sausages.Thesebulk packsare deliveredto supermarkets wherethey areopenedin the preparation areabeforedisplaying the productfor saleasa freshproduct. Modified atmospherepacksin rigid film or traysareused for thinly sliced productsand for products which can damage the film when packed under vacuum. The gas or gas mixture in these packs is very much dependenton thetypeof product, theway in which theproduct is consumedand the type of film used.Skin packsareusedfor high quality expensive products. The film is softenedbefore being skin-drapedonto the product and therefore does not damage it. Difficu lt opening procedures and the high cost of the package are the main disadvantages of this system (Mondry, 1996). Thesousvidemethodof food preparationwasdevelopedin themid-1970sin France (Creed, 1998)andhasfoundwidespreadacceptancethere.Acceptanceof this processing methodhas beenslower in the United Statesand most other Europeancountriesbutcontinuesto grow, particularly in thefoodservicesector. Sousvide involves vacuumpackagingof foods,usually in multilayer laminate plastic pouches,cooking the vacuumpackaged product in a water bath, moist steamor pressurecooker,cooling rapidly in cold waterandthenstoring under refrigeration (Zagory, 1997).It hasbeenwidely claimedthat sousvide food is sensorially andnutritionally superiorto thatproducedusingcook-chill methods. Firstly, the low oxygentensioninsidethepackinhibits bothchemical oxidation andmicrobial activity. Secondly, the packagingpreventsevaporative lossesof waterandflavour volatiles during heattreatment (Church, 1998).The majority of studies undertaken on the microbiological safety of sous vide products concern Clostridium botulinum. The public health risk posedby sousvide is exacerbated by its anaerobic nature which inhibits both chemical oxidation and aerobic spoilage organisms which usually provide the sensory indication of spoilage prior to it becoming unfit for consumption. Thus,a potential risk exists for sousvide products to be palatableyet

microbiologically unsafe(Conneret al., 1989).However, thereis little evidenceto dateto indicatea significant risk Meat packaging 427 except in cases of extreme product abuseresulting from either a lack of uniformity of heattreatment or temperature/time abuseduring chilled storage. Canning is alsoa form of vacuumpackaging which is oftenaccompaniedby thermal processing.Vacuumin the cansmay be obtained by filling completely with theproduct at a high temperatureusing atmospheric pressure.Thevacuum mayalsobeobtainedby machine vacuum,by ‘steam-vac’ closureor by thermal exhausting. The major reasonfor canning meatis to providesafeproductsthat have desirable flavour, texture and appearance. Successful production of commercial ly steri le canned meat products requires that al l viable microorganisms be either destroyed or rendereddormant. The processmust also inactivateraw material enzymesystems.Commercially sterilecannedmeat products generally reach an internal temperature of at least 107ºC, but this temperaturemay be aslow as101ºC,depending on the salt andnitrite content. Somemeat productsmerchandisedin cansreceiveonly a pasteurisationprocess and are referred to as ‘perishable’, which means that they must be kept refrigerated. (PearsonandGillett, 1996).Five principal typesof cansareusedin themeatindustry; squareandpullmanbase,pearshaped, roundsanitary,drawn aluminium, andoblong. The cansusedaregenerally tin or chrome platedlow carbon steelor aluminium.Themost recent developmentin this areahasbeenin the replacement of suchmaterials with PET-aluminium basedlaminates.The resulting product hasan improved flavour, greaternutritional valueandenergy costs are reduced. There are a wide range of meat-based cannedproducts available on the supermarketshelves.The consumer is probablymost familiar with beef stew,chilli con carne, meat balls in gravy, canned hams,spamand tongue and luncheonmeat(PearsonandGillett, 1996). 20.4 Modified atmospherepackaging Modified atmospherepackaging (MAP) is theenclosureof foodproducts in high gas-barrier materials in which the gaseous environmenthas beenchanged to slow respiration rates, reduce microbiological growth and retard enzymatic spoilagewith theintentof extendingshelf-life (Younget al., 1988).Distribution distance is now probably the main factor determining the form of packaging usedfor freshmeats. As discussedpreviously, the central preparation of retail packs is now commonplace within the trading sector. These central cutting systemscanbe operated with product in conventional over-wrappedtrays,but only if times areshortbetween meatcutting anddisplay. For wider tradingof retail-readymeat,a modified atmospheremust beusedto extendthestoragelife of the product (Young et al., 1988). The advantagesand disadvantages of modified atmospheres areshownin Table20.1. MAP systems mostfrequently usemixturesof CO2, O2 and/or N2, in which eachgashasa specific role to play in extending the shelf-life andmaintaining the appearanceof packaged meat (Young et al., 1988).Over a hundredyears ago,a patent wasgrantedfor applying a gasmixtureof CO2 andCO for storage 428 Meat processing of meat.In the1970s,MAP wasintroducedfor retail meat in FranceandtheUK. Themarketshare of MAP in Western Europeancountriesasa percentageof the total retail meatmarket is 10–40%(SorheimandNissen, 2000).However, this methodof meatpackagingis not aspopular in the USA. The demandfor meat packaging in theUSA is led by meatpackingcompaniesratherthanby retailers. In addition, the distribution chain is neitherasquick or ascontrolled asit is in Europe, anddistancesfrom processorto marketaregreater (Taylor, 1996). 20.4.1 Gasesusedin fresh and processedmeat packaging The mostcommonly usedgasesfor the packagingof meatareCO2, N2 andO2 althoughother gasesincluding CO, nitrous oxide, argon,sulphur dioxide and ozonehave beentried to a limit ed extent (Church,1994). The EU classifies packaging gasesas additivesand hasgiven eachof them an E-number. Also according to EU legislation, foodspackagedin modified atmospheresmustbe labelledwith a phraselike ‘Packagedin a protective atmosphere’ (Sorheim and Nissen, 2000).Gasesfor the packaging of meatare seldomusedalonebut in mixtures,which vary according to the application (Sorheim et al., 1997). Oxygen Oneof themajor functionsof oxygenis to maintain theredpigment, myoglobin in theoxymyoglobinstatethat is responsiblefor thebright redcolour associated with freshness. Oxygen pressurelevels over 240mm are thought to greatly increase and extend the fresh appearance of meats(Seideman and Durland, 1984).Removal of oxygenis particularly important for processed muscle foods held in modified atmospheresystems. In most cases,deterioration of meatsis causedby oxidationof meat componentsor spoilageby aerobic microorganisms, both of which areacceleratedin the presenceof oxygen.The level of residual oxygenin processedmeat modified atmospherepacksis therefore an important factorto consider. It maybeattributedto anumberof factors,suchastheoxygen permeability of the packaging material, the ability of the food to trap air, poor sealing of the packwhich may causeair to leak in, or inappropriate evacuation and/orgasflushingprocedures(Smithetal., 1986).Smiddyetal. (2001)reported that measurement of residual oxygen in packs in conjunction with oxygen Table 20.1 Advantagesanddisadvantagesof modified atmospherepackaging(Wolfe, 1980) Advantages Disadvantages Extendedtransit time Visible addedcost Higher quality maintenance Variableproductrequirements Active inhibition of bacteriaandmoulds Not universallyeffective Reducedeconomicloss Colour changeswith red meats Atmospheremaintenance Temperatureregulation Meat packaging 429 permeability of the packaging materials may provide a better insight into applicability of these materials assuitableprotectorsof food during storage. Carbon dioxide Carbon dioxide is a known inhibitor of microbial growth including meat-borne microorganismsandthesepreservative propertieswerereported asearlyas1882 (Finne,1982). Gramnegativespoilage flora of refrigeratedmeat areespecially sensitive to CO2 while lactic acid bacteria are lessaffected (EnforsandMolin, 1984). The inhibitory effectsof CO2 havebeenattributed to alteration of the bacterial cells permeability, pH changes and enzymatic inhibition (King and Nagel, 1967). Thereappearsto be an increase in the lag phaseandgeneration time, which delaystheoverall increaseof bacterialpopulations. Factorssuchas initial bacterial load, time of application, storage temperature and gas concentrationwill affect the desiredendresult. Gill andTan (1980)demonstratedthat the level of CO2 that gavemaximum inhibition for the commonspoilage organismswasapproximately 200mm Hg, equivalent to 26% CO2 in air. That is, for most of the organismsusedin their study, 26%CO2 gavethesameinhibition ashigherlevelsof CO2. Theinhibitory efficiencyof CO2 is increasedat lower temperatures.This is thought to bedue to the fact that the solubility of gasesis much higher at lower temperatures;the CO2 concentration in the medium will increase asthe temperature is lowered. A packaging system usingan atmosphereof carbondioxide alone is now in commercialusefor chilledredmeatsthataretransportedto distantmarkets(Gill andHarrison,1989).The first practical useof modified atmospherescontaining elevatedlevels of carbon dioxideasa preservative in thehandling of freshmeat wasin theshipment of wholebeefcarcassesfrom AustraliaandNew Zealandto GreatBritain in the 1930s(Silliker andWolfe, 1980). Carbondioxide reactswith water to form carbonic acid and can actually dissolve in freshmeatandalso in the fat. As the gasdissolves in the waterof fresh meat, the quantity of gas within the package diminishesand a partial vacuumis generated. This may bring about the collapse of the pack (Hirsch, 1991). Bruce et al. (1992) reported fissures in beef stored in 100% carbon dioxide controlled atmospheres,which they attributed to evolution of absorbed carbon dioxidefrom themeatduring cooking.It is thought thata carbon dioxide level of 5 l/kg wasusedin this study while the optimum level to useto extend chilledstoragelife of redmeats andpork is 1–2l/kg (Gill andPenny,1988)and 2l/kg respectively (Jeremiah et al., 1996). Sorheimet al. (1996) were of the opinion that increasing atmospheric pressuresconcentrations of CO2 had a negative effect on the ability of meat to hold water.Ledward (1970) reported that more than30% CO2 in red meataccelerateddiscolouration. Experiencehas shown that as far as processed meats are concerned,about 95% of applicationscanbe coveredby a standard mixture of 70% N2 and30% CO2. For boiled and cookedmeatproducts the main dangercomesfrom CO2 dissolving in theproduct juice. Too much CO2 will changetheproduct’s aroma andcausesthe packto collapse. Too little CO2 will meanthat after a few days, 430 Meat processing no CO2 will remain in the package. Close monitoring of the gas mixture composition is required. Pre-friedproducts arepacked at higher levels of CO2 (up to 50%). Thesepackagesaregenerally made from rigid film, ascollapsed packsarea commonfeature dueto dissolution of CO2 (Mondry, 1996). Nitrogen Nitrogen is an inert gasand is abundantly availableat relatively low cost,has neithercolour nor odour and is chemically unreactive (Hirsch,1991). It hasa low solubility in bothwaterandfat. In modified atmospheresnitrogen is usedto displace oxygenin order to delayaerobic spoilageandoxidativedeterioration. Another role of nitrogenis to act asa filler gasso as to preventpackcollapse (Day, 1992). Carbonmonoxide The positive effect of carbon monoxide (CO) on meatcolour was known and patented over 100 yearsago (Church, 1994) but as yet CO hasbeenapplied commercially only to a limit edextent in theMAP of meat. TheNorwegianmeat industry hasbeenusing a gasmixture of 60–70%CO2, 30–40%N2 and 0.3– 0.4%CO for the packaging of beef,pork andlamb.Basedon the literature,the presenceof 0.4–1.0%CO in modified atmospheresusedfor the packagingof meat seemssufficient to producea stable cherry red colour (Sorheimet al., 1997).However, theundesirable pink colour,which sometimesarisesin cooked white meat, can sometimesbe linked to exposure to CO also. Sorheimet al. (2001)reported thatpersistentrednessin cookedbeefburgers wasinfluencedby CO. The burgers,containing carboxymyoglobin, were cookedto an end point temperature of more than 80ºC while still having tracesof pink colour and uncooked appearance.However carbon monoxide is a toxic gasandthereforeits usefor food packaging is not allowed in mostcountries. It is not approved for meat packaging in the US or in the EU (Luno et al., 1998). Very little information exists in the li terature on the exposure to CO following the consumption of meat that has beentreated with CO gas but it is considered highly improbable that CO exposure from meat packaged in an atmosphere containing up to 0.5% will represent a toxic threat to consumers through the formation of carboxyhaemoglobin (COHb) (Sorheim et al. 1997). The safetyof workers who come in contactwith carbonmonoxide in meat packaging factories is also a cause for concern. If pure CO or high concentrationsof CO were usedfor mixing of gasesin the plant, they would poseaclear risk. Thepracticeof Norwegiangassuppliersis eitherto deliverCO

asa 1% CO/99% N2 mixtureandthenblendthis mixture with CO2 on site,or as a complete0.3%CO/70%CO2/30%N2 mixture.This practiceis recognised by Norwegian healthauthorities to be safe(Sorheimet al., 2001). In a studycarried out by Luno et al. (2000)it wasshown thatanatmosphere containing 50%CO2 and0.50–0.75% CO in thepresenceof a low concentration of O2 (24%) is able to extendthe shelf life of freshbeef steaksby 5–10 days whencomparedwith thestoragelife in anatmosphereof 70%O2, 20%CO2 and Meat packaging 431 10%N2. Thepresenceof CO and50%CO2 extendsproduct shelf-life by inhibi- tion of spoilage bacteriagrowth, delayedmetmyoglobin formation, stabilisation of redcolourmeasuredby instrumental andsensory techniques,maintenanceof fresh meat odourandslowing down of oxidative reactions(Luno et al. 2000). Jayasingh et al. (2001) recommended the pretreatmentof beef steakswith 5% CO for 24 hoursto ensure a high colour stability beforecontinuing storagein anaerobic conditions. It is thought that the colour of cookedmeatproducts can also benefit from exposure to CO, as1% CO in a N2 atmospherestabilised the colour of bologna(Aasgaard,1993).The reasonfor the colour improvementis unknown but CO may bind to partly undenaturedmylglobin. Sulphur dioxide and argon Sulphur dioxide is very chemically reactive in aqueous solution and forms sulphite compounds, which are inhibitory to bacteria in acid conditions (pH< 4). It hasfoundusein thecontrol of microbial growth in someprocessed meat products, such as sausages. Some people display hypersensitivity to sulphite compoundsin foods and their usehascomeunderscrutiny in recent years. Argon is a noble gasand is not known to haveany chemical or biological activity. However, it is reported to havesome antimicrobial effects. Argon is present in theatmosphere(0.90%)andis therefore relatively abundant (Zagory, 1997). 20.4.2 Modified atmosphereequipment A variety of machinesarenow available, usingmixturesof between 60–80%O2 and 40–20% CO2 for prolonging the useful retail life of fresh meat to approximately a week. The most common of these is the thermoforming machinewhich producestraysfrom a bottomwebof plastic, flushesthemwith a gasmixtureandthensealsthemwith a top webof film. Theuseof modifiedgas atmospheres for thebulk gasflushprocesswasdevelopedin themid-1970s.The basic bulk gaspacking techniqueemploystheuseof a preformedpouchor rigid tray along with a high barrier flexible lidding material. Air surrounding the product insidethepackageis removedandreplaced with a specificgasmixture. The modified atmospheregasmixes usedfor bulk gaspacking,aswell as the performance requirements of the package, differ greatly from those for consumer retail packs. Oxygen is not normally used in bulk modif ied atmospherepacking,sinceextension of caselife of most products depends on the absenceof oxygenThe most commongasmixtures selectedfor different meat productsfor bulk gasflushing canbe seenin Table20.2. Thermoformingmachineshavebeendesignedfor gasflushingof retail sized packsbut canalsobe usedfor bulk packingby removing thesmaller die inserts. Packsof up to 5kg canbe produced at high speeds but they canbe difficul t to handle and tend to be expensive. Snorkel-type machines are specifically designedfor bulk gaspackingof meatandarenowthemostwidely used.Theair 432 Meat processing is evacuatedfrom preformedpouches andreplaced with gasthroughretractable snorkels,which areinsertedinto themouthsof thepouchesuntil just beforeheat sealing (Down, 1996). Modified atmosphere trays are designed to minimise contact with the undersideof themeatandalsobedeepenoughto avoid contactwith thelid. The excessive size of the tray can add considerably to the packaging costs. Tray depthcanbeconsiderably reducedby vacuumskin-packing themeat to thebase of thetray using anO2 permeable plastic.Thespaceabovetheskin-packedmeat is flushedwith a modifiedatmosphere,beforebeing sealedwith a barrierplastic lid. The meat is fixed to the baseof the tray and, therefore, there is less likelihood of accidentalcontact with the lid or tray sides(Taylor, 1996). 20.4.3 The effectivenessof MAP on fresh and processedmeats The composition of the atmosphere within a modified atmosphere package determinesto a largedegree theextentandtypeof spoilage thatdevelopsduring storage. Reportsdiffer concerning theoptimumgasmixturerequiredto maintain satisfactory meat colour and to extend the microbiological shelf life of the product. The most commonly usedgasmixture for fresh red meat is high O2, which hasa minimum of 60–70%O2 and30–40%CO2. Packaging in high O2 extendsthe time for occurrenceof microbiological spoilage anddiscolouration of meat (Sorheim and Nissen, 2000). Gill (1991) stated that modified atmospherescontaining high oxygenconcentrationsessentially doublethe time to spoilage(storagelife) andimprovecolour stability. Accordingto Younget al. (1988), oxygen partial pressures over 240mm greatly enhanceand extend retentionof the freshappearanceof meat.Low O2 MAP is sometimesusedfor bulk packaging product;the inhibitory effects of CO2 areexploitedwithout any particular regard for the preservation of meatcolour (Gill, 1995). ShayandEgan(1990)foundthat the increase in displaylife of retail cutsby modified atmosphere storagedecreased as the time of storagein the vacuum pack increased. However, they concludedthat modified atmospherestorageof Table 20.2 Typical MAP combinationsshowingbulk storagelife (Down, 1996) Bulk MAP Packaging Gasmix Temp Life product (ºC) (max. days) Whole chicken 5L PA/PE 100%CO2 ÿ2 to 0 20–25 Whole turkey 5L PA/PE 100%CO2 0 to 2 14–20 Poultry portions 5LPA/PE 100%CO2 ÿ2 to 0 10– 14 Pork primals 5LPA/PE 40%CO2/60%N2 0 to 2 10–14 Pork primals PA/EVOH/PE 100%CO2 0 to 2 20–25 Beef primals PA/EVOH/PE 80%CO2/20%N2 ÿ2 to 0 42 Lamb primals PA/EVOH/PE 80%CO2/20%N2 0 to 2 21 Curedmeats PA/EVOH/PE 80%CO2/20%N2 0 to 2 21 Wholesalmon/trout 5L PA/PE 80%CO2/20%N2 0 to 2 14–20 Meat packaging 433 beefandlamb in a mixture of 80%O2 and20%CO2 cangive up to a threefold extensionof retail display life. Gill andJones(1996) reportedthat pork chops stored in 67% oxygen and 33% carbondioxide for up to 12 days remained acceptablein appearanceduring48hoursof display.Marriott et al. (1977)found thatatmospherescontaining60%carbondioxide,25%oxygenand15%nitrogen improved the overall retail appearanceand desirability of beef cuts. However, Okayamaet al. (1987)showed that beef steaks,storedin 20% carbondioxide and80% oxygenfor 13 daysat 4ºC underwent a changein surfacepH. Most chilled poultry products are sold pre-wrappedin O2 permeable film, which preventsmoisture lossandthe spreadof contaminating micooorganisms. Relatively little useis madeof MAPdueto highcostandthelack of anymarked advantage in preservation. However, where O2 impermeablefilms are used, mainly for turkeyandduck,thereareclearbenefitsin extendingshelf-life (Hood and Mead, 1993). There have also been reports that high CO2 atmosphere packaging of poultry extendsthestoragelife up to threetimes thatof storagein air (Bakeret al., 1985). Zeuthen and Mead (1996) suggested that 50% of the shelf life of modified atmosphere meats could be attributed to effective chilling (+2ºC during processing, storageand display), 33% to high standardof hygiene during processingwhile the remaining 17%is affectedby thequality of material used. Temperature is probably the most important single environmental factor influencingthe growth of bacteriaon MAP meat (Lambert et al., 1991). The optimum storagetemperaturefor chilled meat is the minimum that can be maintained indefinitely without overt freezing of the product. Gill (1991) statedthat theoptimum temperaturefor packagedmeatisÿ1:5 0:5ºC. Evena small increase aboveoptimum temperature will lead to large lossesof meat storagelife, irrespective of the packaging used.At temperaturesof 0, 2 or 5ºC, thestoragelife is about70,50,or 30%, respectively, of thestoragelife obtained at theoptimum temperature(Gill, 1991). Theimportanceof storagetemperature wasfurther emphasisedby SorheimandNissen (2000)who reportedthat when MAP meatis storedat 8ºC, Salmonella spp.andEscherichia coli, may posea health risk to the consumer. Thesepathogenscan tolerate high carbon dioxide concentrationsandthereforestrict temperaturecontrol is required. Temperature is also important for maintaining the colour of meat. High temperaturesare known to decreasecolour stability. At temperaturesabove3ºC, myoglobin is more readily oxidisedto metmyoglobin (FaustmanandCassens, 1990).At low temperatures,oxygendiffusion into themeatis greaterandsoa deeper layerof oxymyoglobin is formed (Winstanley, 1979). O’Keeffe and Hood (1982) suggested that the rate of discolouration of beef is temperaturedependent and underaerobicconditions,therateof discolouration is two to five timeshigherat 10ºCthanat 0ºC. Under aerobic conditions, the dominant spoilageorganisms are the strictly aerobic Pseudomonads. Glucose is abundantin mostmuscle tissuewhich allows Pseudomonads to grow to numbers of about 108/cm2 before the glucose becomes growth limit ing. The bacteria then attack amino acids as sources of 434 Meat processing growth substrates.While the bacteriaareconsuming glucose,no offensive by- products are producedbut when they commenceutilising the amino acids as food sources,a variety of by-products are produced which are detected organoleptically as putrid odours and flavours (Gill, 1996). High oxygen atmospheresin conjunction with CO2 inhibits growth of Pseudomonadsand allows theslowergrowing organisms,like lactic acid bacteriato dominate. The creation of conditions where lactic acid bacteria predominate are preferred becauseunlikePseudomonads, lactobacilli donotprecipitatespoilagewhenthey are increasing in numbers(Gill, 1991). Ahmad and Marchello (1989) reported that a gasmixture of 10% CO2:5% O2:85% N2 was the most effective modified atmosphere in reducing psychotrophic growth on beef steaks.Buys et al. (1994) found that higher meanpseudomonadcounts were recordedfor 25% CO2:50% N2:25% O2 and 80%O2:20%CO2 bulk packagedsamples thanfor 100%CO2 and75%CO2:25% N2 gasmixtures,respectively. Cookedmeatspacked undermodified atmospheres, containing CO2 as the antimicrobial component,are more prevalent than ever in the supermarket (Devlieghereet al., 1999).However, thereareconflicting reportspublished on the shelf-life extending effect of modified atmospheresfor cookedproducts. Reportedgascompositionsof modified atmospherepackaged processedmeat products areshownin Table20.3. The widespreaduseof modified atmosphere packaging for cured meat productshas generated problems regardingcolour stability of curedmeatproducts storedunderilluminationduring retail display. Light exposure (Andersen et al., 1988) including intensity of light or illuminance,oxygen transmission rate of the packagingmaterial (Yen et al., 1988)andresidual level of oxygen(Moller et al., in press)havebeenfound to affect thecolour stability of cured meat. Resultsof a study carried out by Moller et al. (in press) concluded that it is important to consider all factors simultaneously,whenoptimising the colour stability of cured ham. 20.5 Bulk, master or mother packaging Jeyamkondan et al. (2000) considered master packaging to be the most economical of all centralised packaging

techniques. However, it must be integratedwith strict temperaturecontrol in a narrowrangejust abovefreezing, goodprocessinghygieneandmaintenanceof a completely anoxicatmospherein the package headspacethroughoutthe distribution period to maximise storage life. If properly applied, thestoragelife of retail readymeatcanbeextendedfor up to ten weeksin the master package followed by threedaysof retail display. While processed meatsare not master packagedat present, this method of packaging may be considered safe and reliable for such products where requirementsor applicationsmay arise. It is thought that a ratio of 1:3 in meatto gasvolumeis required to maintain anadequately preservative compositionof theatmospherein a retail pack.Packs Meat packaging 435 Table 20.3 Reportedgascompositionsof processedmeatproducts(Church,1993) Gas(%) O2 CO2 N2 Bacon,cured < 0.5 CO2/N2 Flushed Bacon,sliced – 20–35 65–80 Barbecueribs – 20–40 65–80 Beef, slicedcooked 10 75 15 Chicken,cooked < 0.2 30 70 Chickenthighs,breaded,baked – 30 70 Chicken,breaded,flash fried – – 100 Cookedmeat – 20–25 75–80 Cookedmeat – 20–25 70–75 Cookedmeat – 20–40 60–80 Cookedmeat,sliced – 80 20 Cookedmincedmeatproducts – 20 80 Cornedbeef < 0.3 60 40 Curedmeat – 50 50 Curedmeat – 20 80 Curedmeat – 40 60 Curedmeat,bulk – 35 65 Curedmeat,retail – 20 80 Frankfurters – – 100 Frankfurters – 100 – Ham – 20–35 65–80 Ham, Italian, sliced – 20 80 Ham, sliced that are oversized for the product they contain increasethe distribution and displaycostsperunit andtheyarealsoconsideredunfavourably by thecustomer (Gill and Jones, 1996). Therefore, modified atmosphere display packs in commercial useare often of a size sub-optimal for meat preservation and so confer only a modestextensionof product storagelife (Gill andJones, 1996). Master packaging would alleviate the problems associated with oversized displaypacks. Mincedbeefandbeefsteaksthat aremaster packagedunderN2 and CO2 atmospherescan be stored for three weeks or longer than product freshly preparedfor displayfrom vacuumpackagedmeatof the sameage(Gill andJones,1994a,b). Off-flavour developmentconstituted the limi ting factor in extending thechilled storagelife of display-readypork in controlled atmosphere masterpacks(JeremiahandGibson,1997). It hasbeenreported that the most successful gasmixture in the pouchfor master packagingis 25% CO2, 50% N2 and25% O2 althoughthe odour scores indicatedthat this mixturecouldachievea storageperiodof only 14 daysat 0ºC andsubsequentshelf-life of two days.A studywascarriedout that investigated theinfluenceon theshelf life of freshpork of differentcentralisedprepackaging techniques– PVC overwrapping, MAP using 25% CO2 and 75% O2, vacuum skin packagingandbulk gasflushingof themaster packwith 100%CO2. All of the packagingsystems were equally efficient for the first four days of retail displaybut in theextendedshelf-life study themaster packsystemdemonstrated the most promising shelf-life resultsand was also judged superior on odour scores(Buys,1996). 20.6 Control led atmosphere packaging and active packaging systems Modif ied atmosphere packaging is a packaging system where the pack atmosphere is altered initial ly and then allowed to changeover time during storage. With controlled atmospherepackaging, the package atmosphere is alterediniti ally and then maintainedduring the life of the package (Jeremiah, 2001).Discolourationin controlledatmospherepackagingcanbeprevented only by exclusionof essentially all oxygenfrom thepackage,which requires theuse of special evacuation equipment and totally gas impermeable packaging materials (Gill, 1991). Gill and Jones(1994a,b) reported that discolouration inducedby any residual oxygen in controlled atmosphere packswill resolve after 2–4 days.If CO2 is a major or sole componentof the input atmosphere, then the quantity of addedgas must be adjustedto assure that the intended atmospherepersistsafter dissolution of the gasinto the product(Gill, 1995). For chilled meat, the most effective technology to date is the high CO2 controlled atmosphere packaging system. This regime limits microbial deterioration through optimal storagetemperatures (ÿ1.5ºC), high levels of CO2, low residual oxygen ( 0.05%), and use of a gas impermeable film (Jeremiah et al., 1995). Meat packaging 437 Active packagingis an innovative conceptthat can be definedasa type of packaging that changesthe condition of the packaging to extend shelf-life or improve safetyor sensory properties while maintaining the quality of the food. Major active packaging techniquesare concerned with substances that absorb oxygen,ethylene, moisture, carbon dioxide, flavours/odours and thosewhich release carbon dioxide, antimicrobial agents, antioxidants and flavours (Vermeirenet al., 1999). Themost prevalent form of active packagingin themeat industry is basedon oxygenscavenging.Themajority of commercialO2 scavengersusedin themeat industry arebasedon iron powders, which aremixedwith acidsand/or salts and ahumectant,to promoteoxidationof theiron. Thehumectantmaybedry or pre- wetted(Gill andMcGinnis, 1995).Oxygenscavengersaregenerally formulated to reducetheO2 concentrationin a volumeof air that is five timesthe ratedO2 absorbing capacityof the scavenger to < 100ppm within abouta day, but the time taken to reach thatvaluemayvary from 0.5–4days(Smithet al., 1986).A potential risk associated with O2 scavengersis accidental ingestion of a large amount of iron, in spite of the label ‘Do Not Eat’ on the front of the pack. A welcome alternativeto sachetsis the incorporationof theO2 scavengerinto the packaging structure itself. Low molecular weight ingredientsmay be dissolved or dispersedin a plastic or theplastic maybe madefrom a polymericscavenger. Other recent developmentsinclude inserts in the form of flat packets, cardsor sheets uponwhich themeat product maysit, aswell asO2 scavenging adhesive labels. Someoxygenscavengersuseanenzymereactor surfacethatreactswith some substrate to scavengeincoming O2. Another technique involves sealing of a small coil of an ethyl cellulose film containinga dissolved photosensitivedye andsingle O2 acceptorin the headspaceof a transparent package. Illumination of the film excites dye molecules, which sensitise any O2 moleculesto the singlet state.Thesemoleculesin turn thenreactwith acceptor moleculesandare consumed (Rooney, 1995). In a recent studya naturalantimicrobial agent, grapefruit seedextract,was incorporated on thefood contactsurfaceof multilayeredpolyethylene(PE) film by a co-extrusion or solution coating process and applied to minced beef. Results showed that both types of grapefruit seed extract-incorporated multilayer PE films contributed to a reductionof the growth ratesof aerobic andcoliform bacteriaonmincedbeefwhencomparedto plainPEfilm (Haetal., 2001).Ouatter et al. (2000)undertook a study to evaluatethefeasibility of using antimicrobial films, designedto slowly releasebacterialinhibitors, to improve the preservation of vacuum-packaged processed meats during refrigerated storage. Resultsconfirmedthat the lactic acidbacteria,werenot affectedby the antimicrobial films under study but the growth of Enterobacteriaceae was delayed or completely inhibited asa result of film application. Research in biosensortechnology for the detection of pathogensis very prevalent at present, althoughto date,therehasbeenno commercial success. Belcher (2000)proposed that biosensors will play a big role in the futureof the 438 Meat processing packaging of meatproducts. Biosensorsaredefinedas indicators of biological compoundsthat canbe assimpleastemperaturesensitivepaintsor ascomplex asDNA-RNA probes. Infectiousdosages of pathogenssuchasSalmonella or E coli 0157-H7 areaslow astencells anduntil biosensorshaveadetection limit as low asa singleorganismperml, with rapiddetection andat a low cost,theywill not be considered viable.Two systems,which havebeenrecentlydevelopedto the semi-commercial state in North America are the SIRA ‘Food Sentinel’ systemand the toxin alert ‘Toxin guard’ system. The SIRA ‘Food Sentinel’ systemusesa bar code monitoring system for the detection of specific food contaminants. The second system is for manufacturing flexible packaging materials that candetectandidentify microbial materials in the package. Anotherrecentdevelopmentavailable now on themarketis theCryovacLid 550P/Barrier FoamTray packaging system.This usesa high barrier polystyrene foamtray anda multi-ply lidstock thathasa peelableinterfaceandis theactive part of the process.The product is held at its reduced/deoxymyoglobin state throughoutdistribution but once it reaches the retail store the barrier film is broken at the interface and is peeled off. A high oxygen permeable layer remains,which letsoxygeninto thepackageandallows themeat to returnto the red oxymyoglobin state in 15–30 minutes (Belcher, 2000). A new and innovative product, known as Fresh-R-Pax moistureabsorbing trays, suitable for freshcut meatsandother high purgeitems(manufacturedby Maxwell Chase Technologiesandsupplied by Balitmore Chemicals) is now available. Fresh-RPax moisture absorbing technology is marketedin pad, pouchor tray format (Rowan, 2001). Smiddy et al. (2002) had success detectingoxygen levels in packaged meat products using disposablephosphorescent oxygen sensors, placedin eachpackanda fibre-opticphasedetector. 20.7 Packagingmaterials usedfor meat products A number of simple criteria must be adheredto when selecting particular packaging materials for use with meat products. The package is the primary means of displaying the contained meat product and providing product information and point of sale advertising. The package must also be cost effective relative to the containedfood. The main requirements of any chilled musclefood packageare listed in Table20.4. Plasticfilms arethematerials of choicefor themajority of meatproducts. A plastic film derivesits basicproperties from the monomer unit of the polymer from which it is made.Monomerscomposedof carbon andhydrogen produce polymers suchas polyethylene and polypropylene, which are good barriers to moisturebut relatively permeable to gases.The inclusion of chlorine in the monomerunit greatlyreducesgaspermeability but maymake thepolymerfilm brittle. This problem can be overcomeby adding small quantities of other monomers such as acetals and acrylates which upset the regular polymer structureandmakethefilm moreflexible. Othercompoundsmayalsobeadded Meat packaging 439 to polymers to improve their handling on machines or enhanceparticular properties.Themethodby which thefilm is producedalsoaffects its properties. Most meat packagingfilms arethermoplasticandareextrudedfrom the molten stage throughdies.They can be stretchedto thinner gauges(thickness)before cooling andthis may impart the ability to shrinkwhen reheated(Taylor, 1996). If the properties required of a packaging material cannotbe satisfiedby a single film, severalfilms with individual desirableproperties may becombined to give a satisfactory composite.Thesemay be combined by laminating two or more films together.This is carried out by joining together previously extruded plastic films either by adhesives or by extruding an adhesion polymer melt between the layers. Polymers may be co-extruded together to form a single material by delivering individual molten resins by separate extruders to a combinedroundor flat platedie which maintainstheir separation

in discretebut weldedlayers.A compositecanalsobeproducedby coatinga film with another polymer. In this casea layer of molten plastic resinor a dissolved or dispersed polymer is appliedonto a preformedfilm (Humphreys, 1996).Polyvinylidene chloride and ethyl vinyl alcohol are commonly usedin this way to produce materials with very goodgasandmoisture properties (Taylor, 1996). The choice of films for packagingmeat is largely determined by their moistureandgaspermeabilities. Most of the films usedaremoisturebarriers in order to avoid weight loss from the meat. Gas permeability is much more variable and is specific to individual polymers. For retail cuts of fresh meat where retention of bright red colour is desired, packageswith high oxygen transmissionratesareused.However, for cutsof meatandprocessedproducts where extendedstorage life is the main concern, packageswith low gas transmission rates are used(Newton and Rigg, 1979). The moistureand gas permeabilities of some commonly usedplastic films for meat packagingare shown in Table20.5. A vacuumpackaging film must havemechanical toughness,a high resistance to puncture(especially from bone-in meats) andabrasion,gasbarrierproperties (particularly to oxygen) be adequatefor the application, havesuitableoptical propertiesandtheability to form a sealevenin thepresenceof fat or meat juice Table 20.4 Functionsof a packagingsystemfor chilled musclefood products l Containthe product l Sealintegrity l Be compatiblewith the food l Preventmicrobial contamination l Non toxic l Protectfrom taintsandodours l Handledistributionstresses l Be costeffective l Preventphysicaldamage l Havesalesappeal l Haveappropriategaspermeability l Communicateproductinformation l Control moisturelossor gain l Easily openable l Protectagainstlight wherenecessary l Be tolerantto storagetemperatures l Possessantifog properties l Preventdirt contamination l Be tamperevident l Conformto legal legislation l Conformto environmentallegislation 440 Meat processing andfilm overlap.Thefilms thatbestmeetall theserequirementsarecomposites, which utilise thepropertiesof two or more individualfilm materials to providea good package (Eustace, 1981), eachproviding their own contribution to the structure. Most film products currently usedin Australia for vacuumpackaging freshmeathaveeithernylonor PVDCincluded astheprimarybarrierto oxygen. The individual polymer materials most often usedfor meatvacuumpacksare listed in Table20.6 with their main contributions to the overall structure. During manufacture, shrink bags are stretched both longitudionally and transverselyatacontrolled rateandtemperaturewhichreorganisesthepolymeric chainsandretainsabuilt-in tensionasthefilm is chilled.Later,whenthematerial is exposedto heat,this tensionis releasedandthefilm shrinksin bothdirections. Most shrink bagsavailable on the marketusemulti-ply formulationsbasedon polyolefin resins,with either PVDC or EVOH as the gasbarrier component. Electronic cross-linking is sometimesusedto improvethemechanical resistance of the basic material (Humphreys, 1996). Pouchescan be producedby co- extrusion, adhesive or extrusion lamination.One of the basicpouchstructures usesPA astheouterlayer with aninner coreandsealing layerof PEor LLDPE. Thepropertiesof pouches canbe improvedby incorporatingorientedPA which reducesthesusceptibility of its oxygenbarrier propertiesto moistureor by adding aluminium foil layerswhich canoffer an exceptionally high barrier to oxygen. Heat sealability can be improved by using more expensive EVA or ionomer resins(Humphreys, 1996).For vacuumskin-packaging, thehighly formable top websare basedon ionomer resinswith barrier layersof EVOH and the rigid bottomwebs on polyvinyl chloride(PVC), polystyreneor PET. Table 20.5 Barrier propertiesof plasticmaterialstypically usedin packagingof meat (Roberts,1990) Material (25 micron thickness) O2 transmissionrate Watervapour (cc.m2.day–1.atm.O2 1) transmissionrate 23ºC;dry (g.m– 2.day–1) 38ºC;90% RH EVA (ethyl vinyl acetate) 12,000 110–160 LPDE (low densitypolyethylene) 7,100 16–24 PC (polycarbonate) 4,300 180 PP(polypropylene) 3,000 10 PS(polystyrene) 2,500–5,000 110–160 HDPE (high densitypolyethylene) 2,100 6–8 Nylon 11 (polyamide) 350 60 UPVC (unplasticisedpolyvinyl chloride) 120–160 22–35 Nylon 6 (polyamide) 80 200 PET (polyesterterephthalate) 50–100 20–30 Amorphousnylon 40 20 Aromatic nylon 2.4 25 PVDC extrusion(polyvinylidenechloride) 1.2–9.2 0.8–3.2 PVDC emulsion(polyvinylidenechloride) 0.8–3.4 0.3–1.0 EVOH (ethyl vinyl alcohol) 0.16–1.6 24–120 Meat packaging 441 Thermoforming is now the most common methodof modified atmosphere packaging of meatandmeatproducts.Traysareproducedfrom a bottomwebof plastic, evacuatedandthenflushedwith the gasmixture beforethey aresealed with a top webof film . Thetraysareusuallymadefrom unplasticised polyvinyl chloride (UPVC) or PS and the lidding materials from PET/PS combinations, which may also include a PVDC or EVOH componentto improve gasbarrier properties. Trays are often designedwith patterned basesto dispersethe drip which may accumulate on storagebut in most cases extra absorbent padsare also included. Condensationon the insideof thecontainer lid canbeavoidedby minimising temperaturefluctuationsin thedisplaycabinetandby incorporating an anti-fog coatingon the inner surfaceof the lidding material. Thepropertiesof thematerial from which processed meatpackagesaremade are also of great importance. Optical properties, barrier properties, neutral behaviour regarding taste andsmell, resistance to fats andoils, sealability and Table 20.6 Individual polymer materials, common abbreviation and associated properties Polymermaterials Abbreviations Associatedproperties Low densitypolyethylene LDPE Sealability,formability, moisture barrier, low cost Linear low density LLDPE Sealability,abuseresistance,moisture polyethylene barrier, formability Polypropylene PP Moisturebarrier,thermalresistance, dimensionalstability Ethylenevinyl acetate EVOH Sealability,improvedabuseresistance copolymer over LDPE, clarity Polyesters PET Mechanicalresistance,heatresistance, mediumO2 barrier Ethylenevinyl alcohol EVA High O2 barrier,goodco-extrusion, processability,clarity Polyamides PA Mechanicalstrength,O2 barrier (moisturesensitive),formability Polyvinylidenechloride PVDC High O2 barrier (moisturestable), greaseandfat barrier High densitypolyethylene HDPE More gasimpermeablethanLDPE, low cost,strong,reducedclarity Polyvinyl chloride PVC Versatile,shrink properties,sparkling clear, low cost Polystyrene PS Excellentclarity, low cost,readily themoformedandinjection moulded Ionomer Heatsealability,producefilms of unusualtoughnessandclarity Polycarbonate PC High clarity, strong,impact resistance,dimensionalrigidity 442 Meat processing tightness, thickness and machinability must be considered. In most cases multilayer films are used.The most common materials usedfor packaging of processed meatareshownin Table20.7. 20.8 Future trends Packaging is a prerequisite today demanding distribution of food products globally, nationall y regionally. Product development in meat foods will continue, leading to a wider range of products with increasingcomplexity. Salesof ready-mademealsare increasingandreadymadeproducts containing meatputs high demandson creating a suitable packaging environmentwhich will guarantee quality and maintain or extendshelf-life. Thereis a healthand fitnesstrendsweepingacrossmany countries.Hygienic andecologicaldemands on meat producerswill also increase andthese demandswill affect thechoiceor selectionof materials usedandultimately, the packaging properties obtained. Researchanddevelopment in the areaof activepackaging systemsfor meat products hasreceivedmuchattentionrecentlyandwill continue to do so in the nearfuture.The areasof interestarebio andchemical sensor technologies and anti-microbial agents.Johansson(2001)concludedin a recentreport that food packaging, including the total packaging system, is set to undergo major development changes over the next few years.Theway to facethe challengeis Table 20.7 Materialsusedfor packagingprocessedmeat(Mondry, 1996) Packtype Bottom web materials Top film materials (whereapplicable) Flexible vacuumpack PA/PE,co-extrudedas5 layer-films Flexible MAP pack PA/PE OPA/PE PA/EVOH/PE (O= oriented= prestretched) PA/EVOH/PA/PE PET/PVDC/PE PP/EVOH/PE PE/EVOH/PE Rigid vacuumpack A-PET (amorphouspolyester) OPA/PE PVC or PVC/PE PET/PVDC/PE PS/EVOH/PE OPA/PE/EVOH/PE PET/PE/EVOH/PE Rigid MAP pack PVC OPA/PE PVC/PEor PVC/EVOH/PE PET/PVDC/PE A-PET OPA/PE/EVOH/PE A-PET/PEor A-PET/EVOH/PE PET/PE/EVOH/PE PS/EVOH/PE Skin packs PVC/PE Severalcombinationsof PS/EVOH/PE up to sevenor more layers A-PET but incorporatingEVOH A-PET/PE asgasbarrier Meat packaging 443 the development of barrier materials, a packaging systems review and to see packaging asa meansof reducingenvironmental load in the supplychain. 20.9 References AASGAARD, J. 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Meat packaging 451 ‘A’-‘not A’ test 181–3 accelerated production 381 acetic acid 265, 266 acid taste 372 acidulation 366–7, 380–1 see alsopH actin 34, 35, 372 active packaging systems 437–9 actomyosin 35 adenosine triphosphate (ATP) 198 adhesion 343, 344, 346–7 adjusted temperature coefficient 209, 210 adolescents 84, 85 adult equivalent (AE) 243–4 AFLP 233 aldehydes 114– 15, 374, 376–7 branched 374, 375 alginate 351–2 -linolenic acid 73, 74 alternative forced choice (3-AFC) tests 181 amines biogenic 90–1 heterocyclic 67 amino acids 78–9, 374, 375 amplification 232 anaemia 82–3 analytical methods 394–416 AF spectroscopy 204–6, 401 colour 201–3, 363–4, 398–9 current techniques 397–9 electrical impedance 195–9, 207–8, 398 emerging technologies 399–405 future trends 407–8 genetics 405–7 image analysis 194, 401 immunoassays 232, 403–4 laboratory based methods 395–7 metabolites 404 microbiological hazards 231–3 need for objective methods 395 NIR 201, 204, 401–2 NMR 400 pH 199–201, 397–8 temperature 402 tenderness probe 404–5 ultrasound 399–400 androstenone 181, 207 animal subsystem 241, 242–4, 246, 247–9 animals campylobacteriosis 225 E. coli infections 221–2 salmonellosis 219– 20 welfare standards 20–1 see alsocattle; pigs; poultry; sheep anisotropy 196 antibiotics 233 antimicrobial films 438 appearance 363–5 see alsocolour arachidonic acid 69 Index Arcobacters224,226 argon432 aroma aromacompoundsseevolatile flavour/ aromacompounds fermentedmeatproducts361, 368–71, 372–7 asymmetricinformation8–9 ATPase318 attributes,quality seequality attributes autofluorescence(AF) spectroscopy 204–6,401 automatedslaughterline layout 294, 295 automatedwashingsystems261,263 automaticeviscerationsystem288–90 automation2, 283–96 currentdevelopmentsin robotics284–5 eviscerationprocess287– 90 future trends294–6 andhygiene294 andmanagement294–6 pig slaughtering285–7 secondaryprocesses290–4 boningof the fore–end291–3 boningandtrimming of belly 293 boningandtrimming of loin 293–4 carcasscutting 290–1 cutting of the middle 291,292 hind leg boning293 autoxidation,lipid 108–10,376–7 B vitamins86–7 Bacillus anthracis229 Bacillus cereus229 bacteriaseemicrobiologicalhazards batterpreparation367–8 beef90, 433–4 breedandgeneticeffectson quality 38–44 CLA 147 consumption11–12,13 fat content70, 139–40,142–3,143–4, 145–6 fatty acids75, 76 high concentratediets49–51 modellingcolour stability 124–8,129, 133–4 robotic equipment284 sampling166–7,177–8 sensorycomparisonsbetweencountries 189 US customersatisfactionstudy29–30, 31 beefcattleproduction239–58 challengesfor modellers244–51 elementsof 240–4 future developments254–5 simplemodelof herdstructure251–4 belly: boningandtrimming 293 binders351–2 bioavailability of iron 83 biochips233,407 bioelectricalimpedance198–9 biogenicamines90–1 biohydrogenation75 biosensors438–9 boar taint 181,207 bonehealth89–90 boning belly 293 foreend291–3 hind leg 293 loin 293–4 Bosindicuscattle39–43 Bostauruscattle39, 40–3 bovinemastitis222 bovinespongiformencephalopathy(BSE) 11, 230–1,333 branchedaldehydes374, 375 breed fatness141–2 andgeneticeffectson meatquality 37–49 brittle behaviour342 brucellae229 bulk densitytheory29 bulk packaging435–7 Caliciviridae 231 calpainproteolytic system34, 164,318, 403,406 calpastatin34, 164,406 Campylobacterjejuni 224–6 cancer64, 65, 66–9 candidategenes406 canning427–8 capacitance196 CAPERsystem263 carbohydrates81, 315

aromacompoundsfrom carbohydrate catabolism374–5 carbondioxide 437 absorption124 MAP 430–1 carbondioxide stunning54–5,286 carbonmonoxide431–2 carcass compulsoryclassification21 Index 453 carcass(continued) cutting 290–1 decontamination2, 259–82 problemscausedby irregular surfaces261 measurementsof connectivetissue 204–5 weight andfatness141–2 carnitine91 carnosine90 carryingcapacity,farm 251–4 categoryscales185–6 cathepsins164 cattle breedandgeneticeffectson beef quality 38–44 effect of high concentratedietson beef quality 49–51 pathogenicdiseases219,220,221–2, 225 seealso beef;beefcattleproduction centralisedmeatpackaging417–19 characteristics,quality 8, 17, 18–19 chemicaldecontamination263–7,273,274 chi-squaredtest183 chicken269 seealso poultry children80–1,84 chilling 2, 297–312 impacton colour 300–2 impacton drip loss302–3 impacton evaporativeweight loss 303–4 impacton texture299–300 primary 304 secondary304 temperaturemonitoring306–8 chlorine263,264,265, 274 chlorinedioxide 264, 265,274 cholesterol69, 77–8 choline91 chromaticitycoordinates209–10 CIE colour system209–10,363–4 climate 240– 1,246, 246–7,249–50 Clostridiumbotulinum228–9 Clostridiumperfringens228 coagulation365–6 cobalt110 cold chain304–6 cold room tempering335 cold-shortening(cold-inducedtoughening) 34, 299 cold waterwashing262 collagen37, 162–3,204–6 colorectalcancer(CRC) 65, 66–9 colour 35–7,397,419–21 fermentedmeatproducts361,363–5 colour development364–5 high pressureprocessing319–20 impactof chilling andfreezing300–2 instrumentalmeasurement201–3, 363–4,398–9 on-line monitoring201–3 colour changesduring cooking 209–10 quality indicator159,165 sensorymeasurement363 spectrophotometry194,202–3 colour stability 122–36 externalfactorsaffecting123–31 curedham128–31 freshbeef124–8 modellingdynamicchangesin headspacecomposition123–4 future trends134–5 internal factorsaffecting131–3 meatpackagingand426,431, 432, 434, 435 validationof models133–4 Comitrol processor336 comminution336 Committeeon Medical Aspectsof Food andNutrition (COMA) 65, 66, 138 communication17, 18–19 comparisontests179–81,362 compartmentalisedpackagingodours421 competition14 complexity249 compositepolymer films 440–1 composition analysisof 397,401–2 quality, structureand27–37 computermodellingseemodelling concentration370 concussivestunning54– 5 conditioning299–300 conductivity,electrical398 conjugatedlinoleic acid (CLA) 75–7,89, 137, 146–7,148–9 connectivetissue37, 162–3,317, 401 on-line quality monitoring204–6 consistency56 consumers4, 5 andfat 138 perceptionsof quality 6–14,17–18 testingrestructuredmeat350–1 consumption,meat11–12,13, 65, 147 demand91–2 454 Index energyintake138 recommendationsandcanceravoidance 66–7 contamination260 seealso decontamination controlledatmospherepackaging437–9 convenience12, 418 cookedcured-meatpigment(CCMP) 114, 115, 116 cookedmeats435,436 cooking259 decontaminationprocessesand267, 268, 271 measuringchangesduring 208–11 methodandcancerrisk 68 restructuredmeat distortion347–9,350 losses347, 348 copper110 coronaryheartdisease(CHD) 65, 138 Corynebacteriumpseudotuberculosis229 countries,comparisonsbetween189 credencequality attributes(CQA) 9–11, 16, 18, 21, 22 Creutzfeldt-Jakobdisease,new variant (vCJD) 230–1 CryovacFoamTray packagingsystem 439 Cryptosporidiumparvum229–30 cues7, 17–19 consumersandcueprocessing9–11 culling rates252,253,254 curedmeats colour stability 134 externalfactors128–31 internal factors132–3 flavour quality 113–16 cutting carcass290–1 middle 291, 292 Cyclosporaspp.230 D vitamins87–8 dark, firm anddry (DFD) meat53 Debaryomyceshansenii379–80 decisionframes8–9 decisionsupportsystems245,247, 248, 249, 254 decontamination2, 259–82 currenttechniquesandtheir limitations 260–2 differencebetweenmethodsand treatments261–2 future trends273–6 novel methodsapartfrom steam272–3 problems261 steam262,267–72,273–4 useof chemicals263–7,273, 274 washing262–3 degradationenzymes34–5 ‘Deluge’ system263 demand91–2 seealso consumption deoxymyoglobin419–20 descriptivetests362–3 design,refrigeration308–10 DFD meat53 diet animal effectson fat contentand compositionof meat144–7 influenceson raw meatquality 49–52 human vegandiet 74, 80 vegetariandiet 74, 79–81 differencetests178, 362 diffusion 268 direct extraction370 directionalpreferencetests179 disease cancer64, 65, 66–9 causedby microbiologicalhazards 217–31passim, 259, 297 CHD 65, 138 fat contentand69–71 vCJD 230–1 disinfectionof equipment294 disodiumethylenediaminentetraacetic acid 111 display305 distillation 370 distortion,cooking347–9,350 ‘DNA chip’ technology233, 407 DNA markers405 docosahexaenoicacid 73, 74, 141 domestictransportandstorage305–6 doming348, 349 drip loss167, 298,398, 419 impactof chilling andfreezing302–3 packagingand424,428 drying 366–7,368,381 duo-trio test181,182 E vitamins51, 382,422 eatingquality 6, 157 determining166 experiencequality attributes(EQA) 8, 9–11,16, 21–2 Index 455 eatingquality (continued) quality indicators160–5 standardsfor 21 Echinococcusgranulosus230 economicsubsystem241,244,246,248–9 eicosapentaenoicacid 73, 74, 141 elastin204–6 electricalconductivity398 electrical impedance195–6,207–8,398 electricalstimulation55–6 electricalstunning54–5 electrodepenetrationdepth196–7 electromagneticscanning198 electronicnose371 empiricalmodels244–5 emulsifyingproperties320 emulsions207–8 energyintake138 engineeringspecification309–10 Envirobot285 enzymes34–5 eatingquality andenzymaticactivity 164 effect of high pressure315, 318 lysosomal317–18,318 proteolytic34, 164, 318,403,406 Escherichiacoli (E. coli) 221–4,231, 434 diseasein animals221–2 diseasein man222–4 steamdecontamination270–1 ethics12–14,20–1 ethyl vinyl acetatecopolymer(EVA) 442 ethyl vinyl alcohol (EVA) 440,442 EuropeanUnion (EU) decontamination274, 276 packaging429 standards19–21 evaporativeweight loss298,303–4 evisceration287–90 expenditure65 experiencequality attributes(EQA) 8, 9–11,16, 21–2 externalsensorypanels176 F–line robot series287 farm carryingcapacity251–4 fat componentandquality of raw meat27, 28–32,33 intramuscularfat 28–32,33, 140–1, 159–60,161–2,166–7,206 lipid hypothesis65, 148 sourcesin the diet 71, 72 technologicalquality 159–60 fat content89, 137–53,401 animaleffectson fat contentand composition141–4 CLA 146–7 dietaryeffects144–7 anddisease69–71 fat andthe consumer138 fatness138–41,141–3,144, 148 fatty acidsseefatty acids future trends147–9 on-line monitoring206 fatness138–41,141–3,144, 148 fatty acid binding protein(FABP) gene 406 fatty acids71–8,89, 397 cholesterol69, 77–8 CLA 75–7,89, 137,146–7,148–9 dietaryeffectsin pork 51–2 eatingquality 161–2 fat content139,141,143–4,144–6,148 flavour quality 110 free fatty acidsin fermentedmeat products374,376 monounsaturated73, 139,141, 143, 148 polyunsaturated73–5,89, 139, 141, 143, 144–6,148 saturated72–3,139, 141,143,148 technologicalquality 160 trans fatty acids77 FEEDMAN 245,247, 248,249 fermentedmeatproducts2, 359–93 appearanceandcolour 361,363–5 control and improvementof quality 377–81 flavour 368–72 asfunctional foods382 future trendsin quality development 381–2 products359–60 quality 360–1 sensoryquality and its measurement 361–3 tasteandaroma372–7 texture365–8 fibre-optic probe194, 398–9 fibrinogen352 fixed-choiceprofiling 186 flaking 336,341–2 flame ionisationdetection(FID) 371 flavour 105– 21,166,361 dietary impacts50–1 effect of ingredientson 110–16 456 Index evaluationof aromacompoundsand flavour quality 116–17 fat and30–2,33, 162 fermentedmeatproducts368–72 lipid oxidationandmeatflavour deterioration108–10 on-line testing207 role of lipids 106–8 seealso aroma;taste;texture;volatile flavour/aromacompounds flexible MAP packs427,443 flexible vacuumpacks443 flow (gases)268 flow cytometry232 fluorescence204–6,401 food-borneillnesses217–31passim, 259, 297 food hygieneseehygiene food preparation12 food supplychain3–5,17–18 forage49, 241, 242 fore-ends,boning291–3 forming 337 fracturebehaviour342–3 free-choiceprofiling 186 freezerburn 301,304 freezing197, 297–312 impacton colour 300–2 impacton drip loss302–3 impacton evaporativeweight loss 303–4 impacton texture299–300 pressureassisted320–1 primary 304 restructuredmeat337–8 secondary304 temperaturemonitoring306–8 freshgrillsteak-typeproducts351–2 Fresh-R-Paxmoistureabsorbing technology439 Friedmanvalue184 functional foods79–82,148–9 componentsin meat90–1 fermentedmeatproductsas382 functionalgenomics405, 407 fungi/moulds378,380, 423 gaschromatography(GC) 370–1 gaschromatography– massspectrometry (GC–MS)166 gaschromatographyolfactometry(GCO) 166, 371 gases absorptionin meat124 modellingchangesin headspacegas composition123–31 permeabilitiesof packagingfilms 440, 441 usedin MAP 429–32 seealso under individual gases gelatinisation210–11 gelation320 GEMANOVA model125–8 geneexpression407 GeneralisedProcustesAnalysis (GPA) 187 geneticmarkers43–4 genetics37–49,405–7 genotype141–2,143–4 GermPlasmEvaluation(GPE)program 38–9 Giardia duodenalis229 Giardia lamblia 229 glucono-delta-lactone(gdl) 352 glutathione83, 90, 91 glycogen315 glycolysis318 grain-baseddiets50–1 gram-negativebacteria322, 422 grampositivebacteria322,422 grapefruitseedextract438 grass-fedbeef145–6 GRAZE 245 grillsteaks332, 333–8 fresh351–2 seealso restructuredmeat HACCP 19–20,217 haemiron 83, 84 haemproteins111, 114 haemoglobin37, 55, 202 Halothanegene45–7 ham128–31 hardness365, 366–8 headspacecollection370 headspacegascomposition123–31 health149 diseaseseedisease functional foodsseefunctional foods nutrition seenutrition heatdecontaminationtreatments262 heatinsolublecollagenbonds37 hedonicscales396 seealso sensoryanalysis herdstructuremodel251–4 heterocyclicamines67 heterogeneousassays232 hexanal116–17 Index 457 high concentratediets49–51 high pressureliquid chromatography (HPLC) 370–1 reversedphaseHPLC 371 high pressureprocessing272, 273,313– 31 currentapplicationsandfuture prospects323–4 effect on food components314–15 effectson microflora 321–3 effectson sensoryandfunctional properties318–20 enzymereleaseandactivity 318 andmeatquality 313–14 pressureassistedfreezingandthawing 320–1 structuralchanges315–18 hind leg, boning293 homocysteine87 homogeneousassays232 hot waterwashing263 hunter-gatherersocieties81–2 hydroperoxide-dependentlipid peroxidation110 hydroperoxides421 hygiene260 automationand294 standards19–20 ice contentin restructuredmeat339–40 crystal formation300, 301 imageanalysis194, 401 immersion264 immunoassays232, 403–4 impedance,electrical195–9,207–8,398 impedimetry232 indole 207 infra-red thermometry307–8 inoculationmicrobiology275–6 inspectionquality attributes(IQA) 8, 16 instrumentalanalysis colour 363–4,397,398–9 comparisonof sensoryanalysiswith 186–8 eatingquality 166 emergingtechnologies399–405 fermentedmeatproducts363–4,369–71 flavour volatiles369–71,396 impedance195–9,207– 8,398 on-line monitoring1–2,193–216 pH 199–201,397–8 insurancetheory29 interactiveprototyping249 interfaceproblem246–9 intermediatevalueproductssee restructuredmeat intramuscularfat (IMF) (marbling)28–32, 33, 140–1,159–60,161–2,166–7,

intermediatevalueproductssee restructuredmeat intramuscularfat (IMF) (marbling)28–32, 33, 140–1,159–60,161–2,166–7, 206 iron 82–4,90, 438 prooxidanteffect 110–11 iron deficiency82–3 isoelectricpoint 35 Japan:pork customersatisfactionstudy 30, 33 juiciness28–9,162 ketones374,376–7 KUKA robot 285 laboratory-basedquality methods395–7 seealso analyticalmethods lactic acid 53, 374 decontaminationwith 265,266 lactic acid bacteria378,423 lamb 90, 433–4 automatedslaughtering384 dietary influences51 fat content70, 139, 140 fatty acids75, 76, 139 SpanishandUK sensoryanalysis189 land 241–2,246, 246–7 laserdiffractometer203–4 laserscanning200–1 lateral shrinkage348,349 leantissueseemuscles leg temperaturemeasurement308 light scattering200, 208 linear low densitypolyethylene(LLDPE) 442 linoleic acid 69, 73 lipid hypothesis65, 148 lipids 105–21 aromacompoundsfrom lipid degration 105–10,374,376–7 colour andlipid oxidation319–20 effect of ingredientson flavour 110–16 evaluationof aromacompoundsand flavour quality 116–17 high pressureprocessingand315 oxidationandquality deteriorationin packaging421–2 lipoic acid 90 lipolysis 376 Listeria monocytogenes227–8 loin, boningandtrimming 293–4 458 Index long-termpre-slaughterstress52–3 longissimusdorsi (LD) muscle colour stability 131,132 fat content142–3,161 sampling166– 7,167–8 low densitypolyethylene(LDPE) 442 low-temperature,long-timecooking technique323 lubricationeffect 29 lysosomalenzymes317–18,318 Maillard reaction106–7,108,165 major genes406 malignanthypothermia(MH) 45–7,406 malonaldehyde421 management,automationand294–6 managementmodels245, 254 marbling(intramuscularfat) 28–32,33, 140–1,159–60,161–2,166–7,206 marketsubsystem241,244, 246,248–9 massspectrometry(MS) 371 GC-MS 166 MStester197 masterpackagingsystems418, 435–7 mastitis,bovine222 ‘meat factor’ 83 meatflavour deterioration(MFD) 108– 10,115–16 meatquality schemes15–16 mechanicalproperties342–3 mechanisticmodels244–5 Mediterranean(Southern)type fermented products360, 361,364, 372,377, 380, 381 seealso fermentedmeatproducts metabolites404 metal ions 110–11 methyl ketones377 metmyoglobin165, 201,320, 419–20 microarraytechnology233, 407 microbiologicalhazards2, 217– 36,259–60 analyticalmethods231–3 Campylobacterjejuni 224–6 Clostridiumbotulinum228–9 Clostridiumperfringens228 E. coli 221–4,231,270–1,434 effectsof high pressureprocessing 321–3 future trends233–4 Listeria monocytogenes227–8 main hazards218–31 otheragents230–1 otherbacteria229 packagingand422–3,425, 430,434–5 parasites229–30 Salmonellae218– 21,270,297, 434 Staphylococcusaureus227 temperatureandmicrobiological growth 297–8 Yersiniaenterocolitica226,270 seealso decontamination Micrococcaceae375, 376,378,378–9 micronutrients82–8 seealso vitamins microwavedecontamination272–3,274 microwavetempering335 middle, cutting of the 291,292 minimum growth temperature298 MIRINZ tendernessprobe405 mixing 336–7 modelling beefcattleproduction2, 239–58 colour stability 122–36 copingwith naturalvariability 249–50 interfaceproblem246–9 matchingpurposeandstructure244–6 validationof models133– 4,251 verification of models250 modified atmospherepackaging(MAP) 421,423, 428–35,437 advantagesanddisadvantages429 effectiveness433–5 equipment432–3 flexible andrigid packs427,443 gascompositions436 gases429–32 modellingandcolour stability 122–36 moisturepermeability440,441 moleculartyping 233 monounsaturatedfatty acids(MUFA) 73, 139,141, 143,148 motherpackagingsystems418,435–7 moulds378,380, 423 MS-tester197 multidimensionalscenario249 muscles classification401 colour stability andmuscletypes131, 132 growth 142–3 musclefibre component32–7 structuralchangesdueto high pressure treatment315–18 Mycobacteriumparatuberculosis229 myofibres195 myofibrillar proteins35, 200 myoglobin35–7,131, 159,165, 201–2, 419–20 Index 459 myosin34, 35, 187–8,344–5,346,365–6, 372 myostatin406 myristic acid 73 Napolegene47–9 NationalCholesterolEducationprogram (NCEP)77 NaturalColour System(NCS) 363 naturalvariability 249–50 nearinfrared(NIR) polarised204 spectrophotometry201 spectroscopy401–2 niacin 86 nitric oxide 364, 404 nitrite-freecuring systems116 nitrites 364,422 andcolour stability 132–3 effectson flavour quality 113–16 nitrogen431 nitrosomyoglobin364 nitrosylhaemochrome201 nitrosylmyoglobin420–1 non-directionalpreferencetests179 non-haemiron 83, 84 Northerntype fermentedproducts359, 360–1,364, 366,377, 380–1 seealso fermentedmeatproducts Norwalk-like viruses(NLVs) 231 nuclearmagneticresonance(NMR) 400 nucleicacid basedassays232–3 nucleotides91, 404 nutrition 1, 64–104,149 fatty acidsin meat71–8 future trends88–92 meatandcancer64, 65, 66–9 meat,fat contentanddisease69–71 meatasa functional food 79–82 micronutrients82–8 protein in meat78–9 obesity82, 89 objectiveapproachto quality 5–6,7–8 objectiveanalyticalmethods395,396–7 off-flavours 109, 421 olfactometry371 omnivores81 on-line monitoring193–216 apparatus193–4 boar taint 207 changesduring cooking208–11 connectivetissue204–6 electrical impedance195–9 emulsions207–8 marblingandfat content206 meatcolour andotherproperties201–3 meatflavour 207 NIR spectrophotometry201 pH 199–201 sarcomerelength203–4 water-holdingcapacity203 optical fibres 194,398–9 organicacids264, 265–6,269–70,274 oscillatingmagneticfield (OMF) pulses 272, 273 osteomalacia87, 88 oxygen419–21 MAP 429–30,433,435, 436 modellingcolour stability in meat127, 128, 129,130–1 oxygenscavengers438 oxymyoglobin165, 201,419–20,429 ozone264, 267,274 packcollapse430–1 packaging2, 417–49 bulk, masteror motherpackaging 435–7 centralised417–19 controlledatmospherepackagingand activepackagingsystems437–9 factorsinfluencingquality of freshand processedmeatproducts419–24 future trends442–3 MAP seemodified atmosphere packaging materials439–42,443 permeabilityof packagingfilm 123–4 vacuumpackaging423,424, 424–8 pairedcomparisontests179 palatability28–9,49–50 pale,soft andexudative(PSE)meat45–7, 53–4,197,199,397 paleolithicdiets81–2 palmitic acid 73 pantothenicacid 86 parasites229–30 particlesize340–2 Pasteurellaspp.229 pasteurisation323 pasturesubsystem246,246–8 pathogensseemicrobiologicalhazards Penicillia 380 peptides370–1,372,374, 375 perceivedquality 5–6, 7 permeabilityof packagingfilm 123–4 pH 53 460 Index acidulationandfermentedmeat products366–7,380–1 analyticaltechniques199–201,397–8 breedtype and45, 46 eatingquality 164–5 isoelectricpoint 35 technologicalquality 158–9 phosphatehydrolysis345–6 phospholipids(PL) 106–7,110,421 phosphorus85 pigs pathogenicdiseases219, 221–2 slaughteringandautomation284–96 seealso pork plastic films 439–42,443 polarisation196 policy models245–6,254–5 polyamides(PA) 442 polyesters(PET) 442 polymerasechainreaction232 polymers439–42,443 polyphosphates264,266 polypropylene(PP)442 polyunsaturatedfatty acids(PUFA) 73–5, 89, 139,141, 143,144–6,148 polyvinylidenechloride(PVDC) 440, 442 pork 167,177,434 breedandgeneticeffectson quality 44–9 Halothanegeneeffects45–7 Napolegeneeffect 47–9 customersatisfactionstudies30, 32, 33 dietaryeffects51–2,144,144–5 fat content70–1,139,140, 144 fatty acids75, 76, 139,143, 144–5 PSE45–7,199,397 Pork StressSyndrome(PSS)45–7,406 potentialliveweight gain 248 pouches426,441 poultry 269 automatedslaughtering284 packaging434 pathogenicdiseases219– 20,221,222, 225 pre-breaking335,340, 341 price premium3 processspecification309–10 processingindustries4–5 production17, 18–19 propanal117 proteasome318 proteins67 degradationandaromacompouds374, 375 effect of high pressure315 haemproteins111,114 historicaldevelopmentof diet 81–2 myofibrillar 35, 200 nutritional quality 78–9 sarcoplasmic347 solubility 343–7 proteolysis56, 366, 372 proteolyticenzymes34, 164,318,403, 406 proteomeanalysis405 PSEmeat45–7,53–4,197,199, 397 Pseudomonads423,434–5 pseudofluorescence205–6 pulsedelectric fields (PEF)272,273 pulsedfield gel electrophoresis(PFGE) 233 pulsedlight 272,274 pyrazines375 pyrophosphate346 quality 1, 3–24 circle 16–19 consumerperceptions6–14,17–18 defining meatquality 394–7 eatingseeeatingquality improving meatandmeatproduct quality 21–2 objectiveandsubjectiveviews 5–6, 6– 8 raw meatseeraw meatquality regulatorydefinitions19–21 sensoryquality 360– 1,361–3 supplierperceptions14–16 supplychainand3–5 technologicalquality 157–60 quality attributes(QA) 7, 8–12,17, 18– 19,21–2 credencequality attributes9–11,16, 18, 21, 22 experiencequality attributes8, 9–11, 16, 21–2 inspectionquality attributes8, 16 quality characteristics(QC) 8, 17, 18–19 quality circle 16–19 quality cuesseecues quality function deployment14–15 quality guidanceapproach15 quality indicators157–74 determiningeatingquality 166 eatingquality 157,160– 5 future trends168 samplingprocedure166–8 technologicalquality 157–60 Index 461 quality schemes15–16 quantitativetrait loci (QTL) analysis 405–6 randomamplified polymorphicDNA (RAPD) 233 rankingtests183–4,362 rating scales185 raw materials fermentedmeatproducts377 restructuredmeat333–4 raw meatquality 27–63 breedandgeneticeffects37–49 dietary influences49–52 ensuringconsistency56 future trends57 quality, meatcompositionandstructure 27–37 rearingand52 slaughteringand52–6 storage56 rearingenvironment52 red, soft andexudative(RSE)meat47–9, 53–4 reduced-fatproducts140 reflectancespectra194,209 reflectedradiation308 refrigeration2, 297–312 cold chain304–6 drip loss302–3 evaporativeweight loss303–4 impacton colour 300–2 impacton texture299–300 optimisingdesignandoperation 308–10 temperaturemonitoring306–8 regulatorydefinitionsof quality 19–21 RendementNapole(RN) gene47–9 researchmodels245 resistance196 responsesurfaceplot 125,126 restrictionfragmentlengthpolymorphism (RFLP) 233 restructuredmeat2, 332–58 factorsaffectingproductquality 338–49 cookingdistortion347–9,350 ice content339–40 mechanicalproperties342–3 particlesize340–2 proteinsolubility 343–7 temperature340 future trends351–2 productmanufacture333–8 flaking 336 forming 337 freezing337–8 mixing 336–7 prebreaking335 raw materials333–4 tempering334–5 sensoryandconsumertesting349–51 retail display305 retailers4, 5 reversedphaseHPLC 371 riboflavin 86 rickets87, 88 rigid MAP packs427, 443 rigid vacuumpacks443 RNA amplification232 robotics284–5,287 seealso automation rotation/reflection187 RSEmeat47–9,53–4 safety19–20 seealso decontamination; microbiologicalhazards Salmonellae218–21,270,297, 434 salmonellosisin animals219–20 salmonellosisin man220–1 salt effect on flavour quality 111–13 restructuredmeat339–40,345, 346, 347, 351 effectivesalt concentration344–5 samples samplingprocedure166–8 usingin sensoryanalysistraining 177–8 sarcomerelength34, 163–4,203–4 sarcoplasmicproteins347 satiety82, 89 saturatedfatty acids(SFA) 72–3,139, 141, 143,148 sausage compositionandsize366–7 seealso fermentedmeatproducts scaling187,362 scoring185 scrapie230,231 screening176–7 SDS-PAGE371 ‘secondgeneration’restructuredmeat products352 selenium85, 90 sensitivityanalysis250 sensoryanalysis1, 166,175–92,395– 6 462 Index

categoryscales185–6 comparisonsbetweencountries189 fermentedmeatproducts361–2,362–3 aroma,tasteandflavour 369 colour 363 restructuredmeat349–50 sensorypanelseesensorypanel sensoryprofile methodsand comparisonswith instrumental measurements186–8 sensorytests178–85 sensorypanel176–8,361–2,362–3 generalconditionsfor assessmentof samples178 screeningcriteria andtraining 176–7 usingsamplesin training 177–8 sensoryquality 360–1 measurement361–3 separation370–1 SFK-Danfotechrobot series287 shearforce analysis166 Warner-Bratzlershearforce 39, 40–3, 44, 396 sheep pathogenicdisease219, 221–2 seealso lamb short-termpreslaughterstress53–4 shrink bags426,441 shrinkageduring cooking348, 349 signals17, 18–19 SIRA ‘Food Sentinel’ system439 skatole181, 207 skin packs424,426, 427,443 slaughtering automation284–96 andmeatquality 52–6 snorkelpackagingmachines432–3 sodiumalginate351–2 sodiumchloride111–12,339,340 seealso salt sodiumhalides112–13 sodiumnitrite 364 sodiumtripolyphosphate(STPP)111 soft fat 206 sono-elastography399–400 sousvide 427 spectrophotometry194,202–3 NIR 201 spraydecontaminationsystems261– 2, 263, 264 standards19–21 Staphylococcus375, 376,378–9 aureus227 startercultures366–7,378–80 steamdecontamination262, 267–72, 273–4 SteamPasteurisationSystem(SPS)271–2 stearicacid 73, 141 sterilisationof equipment294 storage56 refrigeration305 domestic305–6 strain theory29 Streckerdegradation375 stress52–4 long-term52–3 short-term53–4 structure363 changesdueto high pressuretreatment 315–18 quality, meatcompositionand27–37 ultrasoundanalysis399–400 stunningmethod54–5,286 subjectiveapproachto quality 5–6,6–7 sulphurdioxide 432 suppliers perceptionsof quality 14–16 problemsof variability of meatquality 395 supplychain3–5,17–18 surfactants261 survival rates252 taste368–71,372–7 seealso flavour taurine79 TBARS test116 technologicalquality 157–60 temperature297– 9,402,434 adjustedtemperaturecoefficient209, 210 measuringchangesduring cooking208 andmicrobiologicalgrowth 297–8 monitoring306–8 restructuredmeat339–40,345,346 seealso refrigeration tempering334–5 tenderness analyticalmethods396,397, 398,400, 402,403 beefandbreedeffect 39–43 chilling, freezingand299–300 connectivetissueand162–3 degradationof muscleproteins56 effect of high pressure318–19 intramuscularfat and29, 30, 161– 2 musclefibre and32–5 tendernessprobe404–5 Index 463 texture166 effectsof high pressure318–19 fermentedmeatproducts365–8 impactof chilling andfreezing 299–300 restructuredmeatandengineered texture352 thaw-shortening299 thawing320–1 thermalcontact307 thermocouples208 thermoforming426, 432,442 thermometers208 thiamin 86 thickness349,350 thrombin352 ‘Toxin guard’ system439 Toxoplasmagondii 230 training sensorypanels176–8 trans fatty acids77 transglutaminase352 transitionmetal ions 110–11 translation187 transmissiblespongiform encephalopathies(TSEs)230–1 transport305, 305–6 trays,packaging426,432,433, 442 triacylglycerols(TAG) 106,107, 110 triangulartests180 Trichinella spiralis 230 trimming belly 293 loin 293–4 trisodiumphosphate(TSP)263,264, 266, 274 TrochanterMajor 308 troponinT molecule403 trust 9, 10 ‘Tween 80’ 261 two from five test184–5 ‘Ulixes Sortierer’ system285 ultrasound194,272, 273,274, 399–400 ultraviolet light (UV) 272,274 unevenlateral shrinkage348,349 uniformity 168 United States(US) 274–5 meatsatisfactionstudies29–30,31, 32 vacuumpackaging423, 424,424–8 vacuumskin packaging424,426, 427, 443 validationof models133–4,251 values12–14,20– 1 variability, natural249–50 variety 168 vegandiet 74, 80 vegetariandiet 74, 79–81 verification of models250 verotoxigenicE. coli (VTEC) 221,222, 223–4 video imageanalysis(VIA) 194 viruses231 vitamins B 86–7 D 87–8 E 51, 382,422 volatile flavour/aromacompounds 105–10,373–7 from carbohydratecatabolism374–5 collection370 concentration370 detection371 evaluation116–17 instrumentalmeasurement369–71,396 from lipid degradation105–10,374, 376–7 origin 374 from proteindegradation374,375 separation370–1 volumeratio 130 warmed-overflavour (WOF) 109,421 Warner-Bratzlershearforce 39, 40–3,44, 396 washing262–3 automatedwashingsystems261,263 water effect of high pressure314, 320–1 washingwith 261–2,262–3,274 water-holdingcapacity(WHC) 35, 158–9, 164–5,203,396 weaningrates252,253, 254 weight loss,evaporative298, 303–4 welling 348, 349 window of acceptibility 28 World CancerResearchFund(WCRF) 66 yeasts378, 379–80,423 yellow fat 206 Yersiniaenterocolitica226,270 Z lines 34 zinc 84–5 464 Index Preliminaries Contents Contributors 1 Introduction 2 Defining meat quality 3 Factors affecting the quality of raw meat 4 The nutritional quality of meat 5 Lipid derived flavors in meat products 6 Modelling colour stability in meat 7 The fat content of meat and meat products 8 Quality indicators for raw meat 9 Sensory analysis of meat 10 On line monitoring of meat quality 11 Microbiological hazard identification in the meat industry 12 Modelling beef cattle production to improve quality 13 New developments in decontaminating raw meat 14 Automated meat processing 15 New developments in the chilling and freezing of meat 16 High pressure processing of meat 17 Processing and quality control of restructured meat 18 Quality control of fermented meat products 19 New techniques for analysing raw meat 20 Meat packaging Index

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