3 Literature Review riia artie - SciELO Colombia · include breed, sex, age, weight, genes, and type of muscle fiber.Some of these factors are not well studied, others have variable

Rev Colomb Cienc Pecu 2016; 29:3-15

Revista Colombiana de Ciencias Pecuarias

Original articles

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Literature Review

¤ Tocitethisarticle:deLimaDM,deCarvalhoFFR,daSilvaFJS,RangelAHN,NovaesLP,DifanteGDS.Intrinsicfactorsaffectingsheepmeatquality:areview.RevColombCiencPecu2016;29:3-15.

* Correspondingauthor:DorgivalMoraisdeLimaJúnior.CampusArapiraca,UniversidadeFederaldeAlagoas,57309-005.Tel:+55-82-34821829.E-mail:[email protected]

Intrinsic factors affecting sheep meat quality: a review¤

Factores intrínsecos que afectan la calidad de la carne ovina: revisión de literatura

Fatores intrínsecos que interferem na qualidade da carne ovina: revisão de literatura

DorgivalMdeLimaJúnior1*,Zoot,DSc;FranciscoFRdeCarvalho2,Zoot,DSc;FelipeJSdaSilva1,Zoot;AdrianoHdoNRangel3,EngAgron,DSc;LucianoPNovaes3,EngAgron,PhD;GelsondosSDifante3,Zoot,DSc.

1Campus Arapiraca, Universidade Federal de Alagoas, Alagoas, Brazil.

2Departamento de Zootecnia, Universidade Federal Rural de Pernambuco, Pernambuco, Brazil.

3Unidade Acadêmica Especializada em Ciências Agrárias, Universidade Federal do Rio Grande do Norte, Rio Grande do Norte, Brazil.

(Received: November 27, 2014; accepted: September 15, 2015)

doi: 10.17533/udea.rccp.v29n1a01

Summary

Thequalityofmeatisamultifactorialparameterdependentontheperspectiveandgoalsofthelinkintheproductionchain.Generally,avarietyoffactorsdirectlyorindirectlyaffectthequalitycharacteristicsofmeatand,therefore,thevalueofmeatproducts.Often,theliteraturedividestheinterferingfactorsintointrinsicandextrinsic.Intrinsicfactorsarerelatedtoanimals;therefore,intrinsicfactorsarelessvariable.Thesefactorsincludebreed,sex,age,weight,genes,andtypeofmusclefiber.Someofthesefactorsarenotwellstudied,othershavevariableinfluenceorarecontroversialandonlyafewareknownandsometimescontrolled.Thus,thisstudyaimedtoreviewsomeintrinsicfactorsthatinfluencethequalityoflambmeat.

Keywords:cooking losses, meat color, tenderness, water holding capacity.

Resumen

Lacalidaddelacarneesunparámetromultifactorialquedependedelaperspectivaylosobjetivosdeleslabóndelacadenadeproducción.Engeneral,unaampliavariedaddefactoresafectandirectaoindirectamentelacalidaddelacarney,enconsecuencia,losvaloresdelosproductoscárnicos.Amenudo,laliteraturadividelosfactoresqueinterfierenintrínsecayextrínsecamente.Losfactoresintrínsecosestánrelacionadosconlosanimales,porlotanto,sonmenosvariable.Estosfactoresincluyenlaraza,elgénero,laedad,elpeso,losgenesy

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de Lima DM et al. Sheep meat quality: a review

eltipodefibramuscular.Algunosdeestosfactoresnoestánbienestudiados,otrostieneninfluenciavariableosonpolémicos,ysólounospocossonconocidosyavecescontrolados.Porlotanto,estetrabajopretenderevisaralgunosfactoresintrínsecosqueinfluyenenlacalidaddelacarnedeovino.

Palabras clave:capacidad de retención de agua, color de la carne, perdidas por cocción, terneza.

Resumo

Aqualidadedacarneéumparâmetromultifatorial,dependentedaperspectivaeobjetivosdoelodacadeiaprodutiva.Geralmente,umagrandevariedadede fatoresafetamdiretaou indiretamenteascaracterísticasdequalidadedacarnee,consequentemente,osvaloresdosprodutoscárneos.Frequentemente,aliteraturadivideosfatoresinterferentesemintrínsecoseextrínsecos.Osfatoresintrínsecossãoreferentesaoanimale,portanto,menosvariáveis.Essesfatoresincluemraça,sexo,idade,peso,genesetipodefibrasmusculares.Algunsdessesfatoresnãoestãobemestudados,outrostêminfluênciavariáveloucontrovertidaesomentealgunssãoconhecidose,àsvezes,controlados.Dessaforma,objetivou-serevisaralgunsfatoresintrínsecosqueinfluenciamnaqualidadedacarneovina.

Palavras chave:capacidade de retenção de água, cor da carne, maciez da carne, perdas por cocção.

Introduction

Currently,theglobalsheeppopulationismorethan1billionheads(FAO,2015).Onaglobalscale,sheepmeatproduction is small,with less than8.6milliontonnes.ThelargestproducersofsheepmeatareChina,India,Sudan,NigeriaandPakistan.ThethreelargestdestinationsforsheepmeatworldwideareChina,EU,andUS,accountingforabout60%ofglobalexports(FAO,2015).

Meat is themost important source of animalprotein for thehumandiet (Lawrie,2005;McAfeeet al.,2010).However,theparametersthatdefineitsdegreeofacceptanceandqualityvarywiththepointofviewandinterestoftheproducer,trade,industry,andconsumers.

Fromanindustrialperspective,qualityisdefinedanddeterminedbyobjectivefactorsrelatingnotonlytothequalitydemandedbytheconsumer,butalsotoindustrialmeatcharacteristics(Osórioet al.,2009).Inthecontextofthesupplychainandmeatscience,theanalysisofcolor,pH,waterholdingcapacity,cookinglosses,tenderness,chemicalcomposition,fattyacidcomposition,amongmanyothers,areallimportantintheconceptofintegratedqualityandthesearchformorehomogeneousproducts.

Besidesbeinginterconnected,qualityparametersdefinedbythefinalconsumerandindustrydependon a long list of other intrinsic (inherent to the

animal) and extrinsic (inherent tomanagement,environment,etc.)factors.Therefore,meatqualityis defined by animal age, sex, and physiologicalstate,and thepost-mortembiochemistryofmuscleand fat, carcass composition, feed contribution toflavour,proteinandfat levels,aswellas theeffectofgeneticsontissuesandmetabolism,preandpostslaughterhandling,andstorage,amongothers(Webbet al.,2005).

In thecaseof lamb,an increase inconsumptionaccompaniedbyademandforincreasedqualityhasbeenobserved.Thissituationforcesthesupplychaintobetterunderstandthefactorsaffectingmeatquality;weneedtoconsiderthenumberoffactorsthataffectthequalityoflambmeat.Themainintrinsicfactorsinterferingwiththequalityoflambmeatarebreed,sex,age,geneticcharacteristicsandtypeofmusclefibres.Theaimofthisworkistodescribehowtheseintrinsicfactorscausechangesinthequalityofsheepmeat.

Intrinsic factors affecting sheep meat

Breed

Breedhasalargeeffectoncarcassmorphology.It is a complex factor anddifficult to assesswhenonlyitseffectsontheamountoffatormeatqualityare considered.The problem lies at the basis ofcomparison,asresultsvaryaccordingtothechosencriterion:samecarcassweight,sameage,samedegreeofmaturity,etc.(Hopkinset al.,2011).Furthermore,

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racialcomparisoniscomplicatedduetodifferencesintheadoptedselectionprogramsbetweencountries(Sañudoet al.,2008).

It is true that there is genetic variationofmeatquality between populations, especially betweenimproved breeds and native breeds.Lambe et al.(2008;2009)showedvariation(p<0.05)infinalpHandtendernessbetweentheTexelandScottishBlackFacebreeds.Changes in tenderness between thesegenotypescanbepartlyexplainedbythedifferenceinthenumberofmusclefibers(Büngeret al.,2009).Breedalso influencesotherparameterssuchas thechemicalcomposition(Table1).

Breedmayalsoinfluenceothernitrogenfractionsofmeat,besidestrueprotein.Esenbugaet al.(2009)observed thatAwassi sheep show lower values(p<0.05) of non-protein nitrogen (2.44 ± 0.07%versus2.91±0.09%)andsmalleramounts(p<0.05)ofnitrogensolubleinwater(5.18±0.13vs.6.30%±0.16%)whencomparedtoMorkaramansheep.

Regarding chemical composition at the samecarcassweight,animalsofbreedswithsmallerframe

sizewillbeolderandhavemorefatthanthosewithlargerframesize(Osórioet al.,2008).BreedssuchasDorperandtheircrosseshavegreateramountofintramuscular fat at the same age than breeds notspecializedformeatproductionsuchasRambouilletbreed (Arvizuet al., 2011).Barkawiet al. (2009)examined two Egyptian fat-tailed sheep breedsobservingthatOssimibreedshowedhigher(p<0.05)fatcontent(4.2%)thanRahmanibreed(3.3%).TheauthorsnotedthatRahmanibreedhadhigherframesizeandlatermaturitywithhigherlevelsofcirculatinginsulingrowthfactor(IGF-I)atdifferentages.

Typically,selectedbreedsformeatproductionhavegreaternumberofmusclefibersandsmalleramountofintramuscularfatperunitareaofmuscle(Büngeret al., 2009;Hopkins et al., 2011). Furthermore,Vaccaet al.(2008)inferredthatdifferencesbetweengenotypesaltertheactivityoflipogenicenzymesinsheepmuscle,suchasΔ-desaturase,andcaninfluencetheamountandcompositionofdepositedfattyacid.

Cholesterollevelsareoftenassociatedwithheartdisease and redmeat is theprimary sourceof thislipid.Fariaet al.(2012)showeddifferences(p<0.05)

Table 1. Physical-chemical characteristics of Quadriceps femoris from three sheep breeds (mean ± SEM*).

Characteristic Breed

Zwartbles Suffolk Oxford down

Dry matter (g/Kg) 22.0a ± 0.20 23.0b ± 0.26 22.8b ± 0.27

Ash (g/Kg) 1.1b ± 0.01 1.1a ± 0.01 1.1a ± 0.01

Protein (g/Kg) 19.0a ± 0.13 18.1a ± 0.18 18.1a ± 0.17

Collagen (g/Kg) 2.3a ± 0.32 2.5ab ± 0.30 2.9b ± 0.31

Myoglobin (g/Kg) 2.3a ± 0.08 2.3ab ± 0.36 2.5b ± 0.36

Intramuscular fat (g/Kg) 1.7a ± 0.27 3.1b ± 0.36 2.8b ± 0.37

pH 5.7a ± 0.01 5.7a ± 0.02 5.7a ± 0.02

Water holding capacity (%) 18.8a ± 0.75 17.9a ± 1.01 17.0a ± 1.03

Lightness index (L*) 48.4a ± 0.72 47.2a ± 0.97 50.1a ± 0.99

Redness index (a*) 8.5a ± 0.40 8.6a ± 0.54 9.2a ± 0.56

Yellowness index (b*) 12.5a ± 0.27 12.1a ± 0.36 13.4a ± 0.34

a,bMeans followed by different superscript letters in the same row indicate significant difference (p<0.05) based on Duncan’s test. *Standard error of the mean. Adapted from Komprda et al. (2012).

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intheorderof5.72mg/gcholesterollowerforTexelxPolwarthlambmeatcomparedtoTexelxCorriedale.

Themarbling degree can influence varioussensory impressions of sheepmeat, especially itsjuiciness.Inastudyevaluatingbreedswithdifferentaptitudes, Cloete et al. (2012) observed that thelower amount of intramuscular fat inmeat fromMerinosheepwasassociatedwithlowerscoresforsensorycharacteristicsofinitialjuicinessandlastingsucculence(after-tastesucculence)whencomparedto sheepofdoublequalitygenotypesor cut. In anextensivereview,Hopkinset al.(2011)hadalreadynotedlowerjuicinessintheMerinogenotype.

There are few studies comparing breed andpost-mortem pH evolution.Hoffmanet al. (2003)observedthatsheepcrossesbetweenmeatbreedsandwoolbreedsdiffered(p<0.05)inpH48hourspost-mortem,withvaluesof5.71and5.79forMerinoxDormerandMerinoxSuffolkcrosses,respectively.Merino breed has a high final pH,which can bederived from the predominantmusclefiber in thebreed.Duetoselectionforproductionundergrazingconditions, oxidative fibers (1 and 2A)may beprevalentinthemuscleoftheseanimals.Thesefibersarecharacterizedbylowlevelsofglycogen,whichiscloselyrelatedtohighfinalpHvaluesinthemuscle(PösöandPuolanne,2005).

Associatedwith juiciness,meat tenderness isanotherattributeinfluencedbygenotype(Martínez-Cerezoet al.,2005).Thedifferences in thedegreeofmuscularity,ageandphysiologicalactionof thecalpain–calpastatin enzyme complex aremainlyresponsible for thevariation in tendernessof lambmeat(Thompsonet al.,2006).

Teixeiraet al.(2005)showedobjectivedifferences(p<0.01) inmeat tenderness betweenBragançano(7.8Kg/cm2) andMirandesa (6.8Kg/cm2) sheepbreeds.Accordingtotheauthors,thesensorypanelalso identified differences (p<0.05) in hardness,assigningscoresof4.1 toBragançanoand just2.8forMirandesa.Inthelateststudy,Ekizet al.(2009)evaluatedthequalityofsheepmeatoffivegenotypes(TurkishMerino,Ramlic,Kivircik,ChiosandImroz)andobserveddifference(p<0.01)inshearforce(kgf)betweengenotypes.

Physical aspects such as color,water holdingcapacityandcookinglossesaredependenttoagreateror lesser extenton thefinalpHofmeat (Table2).The literature describes variations in color scores,juicinessandwaterholdingcapacitybetweenbreeds(Hernández-Cruzet al.,2009;Costaet al.,2011).

Osórioet al.(2008)arguedthatthemostnoticeablechanges are relatedwith physical aspects ofmeat,mainly the colorbecause it has adirect impactonappearanceandconsumeracceptability.Meatcolorisinfluencedbythemusclemyoglobincontentandthe electrical state ofmuscle proteins (Ramos andGomide,2007;Khlijiet al.,2010).Breedinfluencestheamountofmyoglobinpresentinmuscle,asJuárezet al.(2009)showedfortheGrazalemaMerinobreed:3.09mg/gmyoglobin in lactation and 4.01mg/gmyoglobin in the growing phase,whileLebrijanaChurrabreedshowedvaluesof1.61mg/gand2.79mg/gforthesameproductivestages,respectively.

Geneticscanalsoinfluencefattyacidscompositionofmuscle.According toMuchenje et al. (2009),differences among breeds reflect underlyingdifferencesingeneexpressionoractivityofenzymesinvolvedinfattyacidsynthesis,desaturationorchainelongation,andthusdeservemoreattention.

Demirel et al. (2006),Madruga et al. (2006),andMarinoet al.(2008)observeddifferencesinthelevelsofmonoandpolyunsaturated fattyacids fordifferent sheepbreedsandattributed it todifferentdeposition rates of intramuscular triacylglycerolsin adipocytes associatedwith a dilutive effect ofmembranephospholipids.

Sex

Proximatecompositionofmeatisaffectedbysex,especiallyfatcontent(Peñaet al.,2005;GerrardandGrant,2006;Pérezet al.,2007).Meatfromfemalesisoftenricherinlipids.Santoset al.(2007)observedthatnativeanimalsfromSpainhadhigher(p<0.05)lipidslevelsinthemeatoffemale(2.3%)comparedwithmalelambs(1.9%)ofthesameage.Rodríguezet al.(2008)alsofounddifferences(p<0.05)inthefatcontentofmeatfrommalesandfemales(1.6vs.2.9%,respectively)inAssafsheep,attributingthesedifferences (p<0.05) to the amount of carcass fat,

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Table 2. Meat quality parameters of longissimus muscle as affected by lamb genotypes (mean ± SEM*).

Variable Genotype1 p-value

CA ACA RA ARA A

pH 5.59 ± 0.1 5.75 ± 0.1 5.63 ± 0.1 5.89 ± 0.1 5.58 ± 0.1 0.14

Cooking losses (%) 27.6 ± 1.5 29.3 ± 1.5 27.7 ± 1.5 28.2 ± 1.5 29.8 ± 1.5 0.81

Water holding capacity (%)

21.5 ± 1.2 20.8 ± 1.2 21.6 ± 1.2 21.7 ± 1.2 21.4 ± 1.2 0.99

Shear force (Kg/cm2) 2.28 ± 0.2 1.49 ± 0.2 1.87 ± 0.2 1.91 ± 0.2 2.03 ± 0.2 0.17

Color

Lightness index (L*) 36.6 ± 1.1c 40.4 ± 1.1b 38.2 ± 1.1bc 41.0 ± 1.1ab 43.61 ± 1.1a 0.001

Redness index (a*) 5.39 ± 0.4 5.57 ± 0.4 5.39 ± 0.4 5.31 ± 0.4 5.40 ± 0.4 0.37

Yellowness index (b*) 10.9 ± 1.4 11.7 ± 1.4 10.5 ± 1.4 12.9 ± 1.4 12.60 ± 1.4 0.68

Chroma 12.5 ± 1.1 13.2 ± 1.1 12.5 ± 1.1 14.4 ± 1.1 14.4 ± 1.1 0.55

H-Angle 60.6 ± 4.6 62.3 ± 4.6 57.9 ± 4.6 63.4 ± 4.6 61.0 ± 4.6 0.94

a,b,c Different superscript letters in the same row indicate significant differences based on the stablished p-value. 1Genotypes: CA = F1 Charollais-Awassi; ACA = B1 Awassi-Charollais-Awassi; RA = F1 Romanov-Awassi; ARA = B1 Awassi-Romanov-Awassi; A = Awassi. *Standard error of the mean. Adapted from Abdullah et al. (2011).

beinghigherinfemales(10.9%)thaninmales(8.6%).Whenintactandcastratedmalesarecompared,meatfromcastratedanimalshashigher(p<0.01)fatcontent(Haddadet al.,2006;Warrenet al.,2008).

Physicalparametersofmeatqualityareinfluencedbysex.Johnsonet al.(2005)evaluatedmuscleandmeat deposition ofTexelmale and female lambs,observing increased (p<0.01)depositionofmuscleand less fat inmales for variables adjusted to thesamecarcassweight.Inthesamestudy,meatqualityreflecteddifferences(p<0.01)forgenderintenderness(74.5Nforfemalesand82.4Nformales)andfinalpH(5.60forfemalesand5.74formales).

Decreasing pH is influenced bymany factors,amongwhichglycogen,ATP,andcreatinephosphatereservesarethemostdeterminant.McGeehinet al.(2001)observed thatpHdrop is faster (p<0.05) infemalesthaninmales,withconstantdifferencesof0.18pHunits.Itcanbeinferredthatglycogencontentinfemalesishigherduetolesssexualactivity.Anotherpossible hypothesis is that the higher reactivity ofmalesispromotedbytestosteroneanddepletesmuscle

glycogen faster via catecholamines.Adrenalinerecruits glucose to the bloodstreamand stimulatesmuscleglycolysis(PösöandPuolanne,2005).

OkeudoandMoss(2008)evaluatedtheinfluenceofsex(intactmales,castratedmales,vasectomizedmales,andfemales)onmeatqualityofsheep(Table3).

Thedifferencesincookinglossesandshearforcebetweenmalesandfemalescanbepartlyexplainedbyhigherintramuscularfatcontentoffemales(OkeudoandMoss,2008).Inreviewingaspectsofmeatquality,KoohmaraieandGeesink(2006)claimedthatfathaslowerwatercontentthanmuscle;therefore,musclesricher in adipose tissue have reducedwater loss.Moreover,authorspointoutthatagreateramountofadipocytesimpliesthattheamountofmusclefibersperareaisreduced,therebyfavouringsmallershearforcevalues.

Frequentdifferencesinmeattendernessarefoundformostspeciesbetweenintactandcastratedmales.Lageet al. (2009) observed higher shear strengthandsmallervaluesforthemyofibrillarfragmentation

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Table 3. Effect of sex on sheep meat quality.

Sex pHi# pHf# Sarcomere length (μm)

Cooking losses (%)

Shear force (Kg)

Castrated males 6.45 5.67 1.72 21.67b 6.04ab

Intact males 6.51 5.73 1.75 20.43b 6.65b

Vasectomized males 6.54 5.69 1.73 20.42b 7.03b

Females 6.52 5.69 1.77 17.64a 5.35a

Standard error 0.065 0.037 0.036 1.369 0.617

Significance NS NS NS * *

a,bMeans followed by different superscript letters in the same column indicate significant difference (p<0.05). #pHi = initial pH; pHf = final pH. NS = not significant, * (p<0.05). Adapted from Okeudo and Moss (2008).

index inLongissimus dorsi of castrated comparedtonon-castratedanimals.Theauthorsalsoobservednodifferenceinm-calpainandμ-calpainactivity24hourspost-morteminrelationtosex.Calpastatinwas 81%higher in intact animals comparedwithcastratedmales.Besides high calpastatin activity,anotherexplanationforthelowmeattendernessofnon-castrated animalswould be their higher zincconcentration,whichisapotentinhibitorofcalpain(Koohmaraie andGeesink, 2006). Furthermore,Gökdalet al.(2010)foundhigher(p<0.05)collagencontentinmeatfromintactmales(4.03±0.44mg/g)comparedtoimmunologicallycastratedmales(2.52±0.28mg/g).

Sexdifferencesforfattyacidcontentaredocumentedin the literature. Tejeda et al. (2008) showeddifferences (p<0.01) in fatty acid composition ofLongissimus lumborumofMerinomalesandfemales.Theyassociatedittohigherlevelsofpolyunsaturatedfattyacidsinintactmales.Intramuscularfatismoresaturatedthanmembranephospholipidsforexample,andfemaleshavehigherdepositionofintramuscularfat.Therefore,itiscommonintheliteraturetorefertofemalesheepmeatasbeingmoresaturated.

Inaddition to fattyacidcomposition,castrationaffects cholesterol levels of meat frommales.According toMadruga et al. (2001), castrationincreased(p<0.05)cholesterolinmeatfromcastratedgoats(62.5mg/g)comparedtothatofintactanimals(58.0mg/g). It can be inferred that cholesterolmobilization by intact animals is higher because

steroidhormonesarederivedfromthislipid,whichcontributestolessdepositionofthismetaboliteintothemeat.ThesensorypanelratedbyNavajaset al.(2008)andTejedaet al.(2008)classifiedthemeatofintactmaleswithhigherscoresfor“badtaste”.

Age and body weight

Thesefactorsareanalyzedtogetherbecauseifnomanipulationoffoodoccursortheanimaldoesnotsufferseverefoodrestriction,agreaterweightinthesamegenetic background implies greater age.Theslaughterweight affects consumer acceptability inmanycountries(Martínez-Cerezoet al.,2005;FontiFurnolset al.,2006;Muelaet al.,2010)andthereforedeservesspecialattentioninthestudyofmeatquality.

The growth curve of sheep is sigmoid,with aperiod of accelerated lean tissue deposition thatcoincideswith puberty and a stabilization periodof protein deposition and increased fat depositionknownasmaturity.Theincreaseinproteindepositionis mediated by growth hormones (GH), whichincreasemusclefibers hypertrophy and reduce fathormonesdeposition.Theincreaseinfatdepositionamounts to the extent that sex hormones increasetheirconcentrationinthebloodstream(GerrardandGrant,2006).

Differencesinsheepmeatqualityatdifferentagesnecessarily correspond to changes in the amountof carcass fat and its relationship to physical andchemicalaspectsofmeat (Table4).Barkawiet al.

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(2009)evaluatedthechemicalcompositionofmeatfromnative lambsat twoages(270and360days)andobservedareduction(p<0.01)ofmoisture(75.8to75.1%)andanincrease(p<0.01)infat(3.3to4.2%)withincreasingslaughterage.

Regardingcolor,theincreasedweightandageatslaughtertendtoincreasetheamountofpigments,redcontent(a*)andreducedluminosity(L*).Juárezet al.(2009)observedanincrease(p<0.01)inmyoglobin(3.09to4.01mg/g),low(p<0.01)luminosity(45.10to40.19L*)andincreased(p<0.01)redness(7.35to9.79 a*)with increasing (p<0.01) slaughterweightofGrazalemaMerinosheepbreed.Inanotherstudy,Teixeiraet al.(2005)identifiedareduction(p<0.05)inL*of40.0±0.55to39.0±0.54whenslaughterweightincreasedfrom9-14to19-24Kg.

Silva Sobrinho et al. (2005) evaluatedmeatquality from lambs of different exotic genotypesslaughtered at two ages.They found thatWarnen-

Bratzlermeasurementwas higher inmeat fromanimalsslaughteredat300dayscomparedto150daysatslaughter,indicatingthatlargershearforceswererequiredtocutthesamplesfromolderanimals.Tejedaet al.(2008)studiedthetexturecompositionofsheepmeat at different slaughterweights (24 or 29Kg)observinghighermeatfibrosityat29Kgbodyweight.Thisparameterwasrelatedtoincreasedthermalandmechanicalstabilityofcollagen(Purslow,2005).

Regarding juiciness,meat fromyoung animalsshouldbemoisteratthefirstbiteandhaveadrierafter-taste,whileheavierandolderanimalshaveatendencytowardgreaterjuicinessduetofatcontent.Corroboratingthisassertion,Juárezet al.(2009)reportedhigherendjuicinesswithincreasingageatslaughter.

Russoet al.(2003)evaluatedthequalityofbeefcarcasses,observinghigherwaterholdingcapacity(0.33 for light, 0.36medium and 0.39 for heavycarcasses);however,theincreaseinslaughterweight

Table 4. Parameters of Semimembranosus muscle meat quality of Awassi sheep slaughtered at different weights.

Item Slaughter weight Standard error Significance

20 Kg 30 Kg 40 Kg

pH 5.92 5.90 5.88 0.03 NS

Cooking losses (%) 44.0 44.0 42.3 1.1 NS

Water retention (%) 26.1a 24.6a 20.9b 0.9 ***

Shear force (N) 35.9b 35.9b 41.8a 1.5 **

Color

Lightness index (L*) 40.49a 38.09b 36.33c 0.5 ***

Redness index (a*) 3.77b 5.03a 5.34a 0.3 ***

Yellowness index (b*) 14.56 13.88 14.17 0.4 NS

Chroma 15.14 14.63 15.22 0.4 NS

H-Angle 75.1a 69.6b 68.5b 1.4 **

Chemical composition (%)

Moisture 77.1a 75.8b 75.4b 0.4 *

Protein 19.4 19.6 19.9 0.3 NS

Fat 2.30b 3.30a 3.10a 0.3 *

Ash 1.07 1.05 1.09 0.02 NS

a,b,cMeans followed by different superscript letters in the same row indicate significant difference based on the established p-value. NS = not significant; * = p<0.05; ** = p<0.01; *** = p<0.001. Adapted from Abdullah and Qudsieh (2009).

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also increased cooking losses. It can be inferredthatsheepmeattakeslongertoreachthedegreeofdoneness(70°Cinthecenterofbeef)asageincreases,resultinginhigherlosses.Nevertheless,Pinheiroet al.(2009)observedcontraryresults,reportinghighercookinglossesinlambs(46.44%)comparedtoadultsheep(39.33%).

Theinfluenceofweightandslaughterageonfattyacidcompositioninsheepmeatisquitecontroversial.Some results indicate no influence of slaughterweightonthefattyacidcompositionofmeat(Díazet al.,2003).However,Woodet al.(2008)reviewedtheinfluenceofageonfattyacidsconcentrationsinadiposetissueofruminantsandreportedanincreasein the proportion ofmonounsaturated fatty acids.Accordingtotheauthors,theproportionofsaturatedfatty acids fallswhile linolenic acid levels remainconstant.Thisstudyalsoshowedthattheproportionofconjugatedlinolenicacid(CLA)inthefatincreasedwiththeageoftheanimal.

Warrenet al.(2008)analyzedfattyacidscontent,triglycerideslevels,andphospholipidsinAberdeenAngus cattle at three different ages (14, 19, and24months).Theauthorsobservedtheextenttowhichfattening progresses increasemuscle triglycerides;however,phospholipidsremainreasonablyconstant.Thephospholipidstototallipidsratiofellby30%at14monthsand12%at24months,andthesedecreaseswereaccompaniedbyanincreaseintheproportionofmonounsaturatedfattyacidsandadecreaseofω-6polyunsaturatedinthetotallipids.Thisseemstobesimilar in sheep, asMarinoet al. (2008)observedincreasingsaturatedlipidsanddecreasingunsaturatedlipids in intramuscular (Longissimus dorsi) fat ofsheepnativetoItaly.

Genes

The studyof gene influenceonmeat quality isrecentanditsimplicationsarestillpoorlyunderstood(Thompsonet al.,2006). Insheep, themainsetofgenes (loci of quantitative traits) affecting carcasscharacteristicsandmeatare:Callipyge,Carwellorribeyemuscling(REM),Doublemuscling(Cockettet al.,2005).

Recently,theexistenceofagenethatcausesmusclehypertrophy in sheepwas identified. Preliminaryevidence suggests an autosomal dominant genemay be responsible for this effect inmuscle andcarcasscomposition.Comparedwithnormallambs,“Callipyge”lambshave32.30%superiormuscularity,withnochangeinbirthweight.Anadvantageofthe“Callipyge”phenotypeisthatunlikedoublemusclingincattle,theconditioninsheepdoesnotoccuruntilafewweeksafterbirth.Sodystociaatbirthisnotaproblemforcarrieranimals(SosnickiandNewman,2010;Masriet al., 2011a).Despite theadvantagesinweightandcarcassyield,themeatisconsideredextremely tough and somewhat bland due to lowmarbling (Goodson et al., 2001).Meat toughnesscanbeattributedtohighlevelsofcalpastatin,whichinhibitthecalpainsystem-enzymesresponsibleforproteolysisofmusclepost-mortem(KoohmaraieandGeesink,2006;Kempet al.,2010).“Callipyge”sheepmeat presents significant decrease ofmyofibrillarfragmentation, indicative of a decrease in proteindegradation(Hopkinset al.,2011).Kuberet al.(2003)observed that calpastatin activity in “Callipyge”phenotypewas58%higherthanthenormalgenotype,whileAbdulkhaliqet al. (2007) reported2.9 shearforce (kgF) for “Callipyge” sheep and 5.4 for thenormalgenotype.

Besidestheincreasedhypertrophyof“Callipyge”sheep, changes inmuscle fiber type occur.Thismutation increases theamountofglycolyticfibers,whichreduceoxidativemetabolism.Thus,itcanbeinferred that themuscles of “Callipyge” aremoresensitive to a sudden drop in pH (Warner et al.,2010).ChangesinpHmayberesponsibleforhighercookinglosses(31%formutantand29.6%fornormalgenotype;Abdulkhaliqet al.,2007).

Anothermutation in sheepgenome influencingcarcass andmeat qualitywas documented in PollDorsetsheepinAustralia.The“Carwell”phenotypehas8-10%ribeyeareaincrementsatsimilarcarcassweights (Warner et al., 2010). Significant effectsonmuscularity, an increase in protein depositionandup to35%meat toughness increasehavebeendocumented in “Carwell” sheep (Warner et al.,2010).However,Hopkinset al.(2007)reportedno

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increase (p>0.05) in sheer forceofLongissimusorsemimembranosus,oranyothereffectsonpHormeatcolor.Itcanbeinferredfromthecurrentliteraturethattheeffectsof the“Carwell”phenotypeare far lessimpacting onmeat quality than those documentedbythe“Callipyge”phenotype(Hopkinset al.,2011).

AccordingtoMcFarlaneet al. (2005),myostatincontrolsmusclefiberproliferationthroughtranscriptionofgenegroupsresponsibleformyoblastsandfibroblastsdifferentiationandtheirsubsequentaggregationinthemyotube.Amutationinthemyostatin(GDF8)generesultingininhibitedtranscriptionhasbeenshowntoincreasemuscularityinTexelsheepandotherbreeds(Clopet al.,2006).Otherstudieshavereportedthatmyostatinmutationsinfluencemuscleandfat(Kijaset al.,2007;Lambeet al.,2011).

The g + 6723GNAmutation increased thepercentage of glycolytic fibers, but did not affectshearforce.However,areductionof intramuscularfat and sensory scores on overallmeat quality,includingjuiciness,wasobserved(Kijaset al.,2007;Hopkinset al.,2011).Masriet al.(2011b)observedthatmyostatinmutations inTexel andPollDorsetbreeds reduceLongissimus intramuscular fat.Theauthorsrecommendpayingattentiontomeatquality,especiallyjuiciness,ofmutantanimals.

InanotherstudyevaluatingmeatqualityofmutantmyostatinTexel sheep observed thatLongissimusandSemimembranosusshearforcewasnotaffectedbythemutation(Johnsonet al.,2005;Lambeet al.,2011).AccordingtoWarneret al.(2010),myostatinmutationsinsheepdonotseemtohaveanyinfluenceonshearingforce,despiteareductionintheperceptionofjuicinessbyconsumers,perhapsduetoareductionintheamountofintramuscularfat.

Besidesamountoffat,fattyacidcompositionofmutantbeefandsheepdeservesattention.Raeset al.(2003)showedthatthedouble-musclinggenotypeincattlehaslowerproportionofmonounsaturatedandhigherofpolyunsaturatedfattyacidscomparedwiththenon-mutantgenotype.Theauthorsattributedthistoalowconcentrationoftotallipidsinmuscleandahigherproportionofphospholipidsinthetotallipids,increasedbythemutation.Thus,studiesontheimpact

ofdouble-musclingonfattyacidcompositioninbeefandsheeparerequired.

Muscle fibers

Differences in muscle fibers correspond tovariations in the type ofmyosin chain (light orheavy) responsible formyofibril contraction.Thispolymorphism affects the enzymatic compositionof thefiber, its buffering capacity and its biology(Gerrard andGrant, 2006; Bünger et al., 2009).Despiteseveralnomenclaturesinmeatscience,threetypesofmusclefiberswithdifferentcharacteristicsaredescribed(Table5).

The number and type ofmuscle fibers of thespeciesaffectmeatcolor.Insheep,theproportionofred,intermediateandwhitefibersisapproximately15, 31 and54%, respectively (Gerrard andGrant,2006). For the same species,Gallo et al. (2009)reportedfrequenciesof9.77,35.01,and55.21%forred,intermediateandwhitefibers,respectively.Theproportionsofthesefibersvarybetweenmusclesandalterphysical-chemicalcharacteristicssuchascolor(Tschirhart-Hoelscheret al.,2006).

In sheep, higher final pHvalue corresponds toslow-contractingmuscleswhile lower final pH isrelated to themore rapidly-contractingmuscles(Thompson et al., 2006;Tschirhart-Hoelscher et al., 2006).Ryu et al. (2006) reported a negativecorrelationbetweentheamountofwhitefibersandthefinalpHofthemuscle.

InadditiontopH,fibertypeandtheirinteractionwith calpastatin activity affectmuscle softness(Table6).However, the effect offiber type is stillcontroversialregardingsoftness(Leeet al.,2010).

Thewatercontentinmusclegreatlyvarieswithincreasing speed ofmuscle contraction.Musclesrich in white fibers are larger and have morewater compared to proteins (Tschirhart-Hoelscheret al., 2006).According toLee et al. (2010), thewater/protein relation affects the ability to retainwater,whichdecreasesbyincreasingthisratio.Thus,lesswaterholdingcapacityandhighercookinglossesareexpectedinrapidlycontractingmuscles.

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Table 5. Characteristics of animal muscle fibers.

Characteristic Red Intermediate White

Red Intensity ++++ +++ +

Myoglobin content ++++ +++ +

Fiber diameter + + ++++

Contraction speed + +++ ++++

Resistance to fatigue ++++ +++ +

Contractile action Tonic Tonic Phase

Buffering capacity + +++ ++++

Number of mitochondria ++++ +++ +

Size of mitochondria ++++ +++ +

Capillary density ++++ +++ +

Oxidative metabolism ++++ ++++ +

Glycolytic metabolism + + ++++

Lipid content ++++ +++ +

Glycogen content + + ++++

+ = Low; +++ = Median; ++++ = High. Adapted from Gerrard and Grant (2006) and Lefaucheur (2010).

Table 6. Content of slow chain myosin (MHC-S) and fast chain myosin (MHC-f), fiber type distribution (Type I and II), shear force, and calpastatin activity in skeletal muscle of sheep.

LD TFL ST SS TZ SE P

MHC-s 1.30 0.42 1.52 4.06 4.62 0.725 <0.001

MHC-f 2.01 2.02 1.79 0.79 1.30 0.370 <0.05

% type I pH 4.6 8.90 8.10 16.8 30.7 54.5 4.23 <0.001

% type II pH 4.6 91.1 91.9 83.2 69.3 45.5 4.23 <0.001

% type I pH 10.4 7.50 5.70 13.3 35.8 45.3 3.49 <0.001

% type II pH 10.4 92.5 94.3 86.7 64.2 54.7 3.49 <0.001

Shear force 4.16 5.35 5.88 5.11 - 0.51 <0.05

Calpastatin activity 1.16 1.37 0.44 0.44 0.46 0.064 <0.001

LD = Longissimus dorsi; TFL = Tensor fasciae latae; ST = Semitendinosus; SS = Supraspinatus; TZ = Trapezius. SE = Standard error of the mean. Adapted from Sazili et al. (2005).

Perspectives

Manyfactorsinfluencesheepquality,andknowledgeoftheirrelevancerequiresmorestudyaccompaniedbyconstantresearchonconsumerandindustrydemands.Intrinsic factors suchasbreed, sex, ageandweight

at slaughter,genes,musclefiberplasticityandmeatqualityreferringtothesefactorsmustbeconsideredinmanagementpractices.Duetotheinfluenceofintrinsicfactorsonmeatcharacteristics,qualitystandardsmustbeknownbylambproducersinordertodefinethetypeofanimalrequiredtomeetthesedemands.

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Conflicts of interest

Theauthorsdeclaretheyhavenoconflictsofinterestwithregardtotheworkpresentedinthisreport.

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Documents

3 Literature Review riia artie - SciELO Colombia · include breed, sex, age, weight, genes, and type of muscle fiber.Some of these factors are not well studied, others have variable