Influence Of Stepwise Chilling On Meat Quality And Postmortem Bovine Muscle Proteome

Tenderness is considered as the most important index to evaluate beef quality,and many factors,such as animal breed,muscle type,pre-and post-slaughter treatments,could have a significant impact on it.Previous studies have indicated that controlling the temperature of the carcass during the first 24 h after slaughter can significantly improve meat quality.After the slaughter,animals were quickly moved to the chilling room,which not only could reduce carcass temperature as soon as possible and inhibit microbial growth,prolonging the shelf-life of the product,but also could regulate the time-temperature-pH relation,which changes the role of endogenous enzyme and the extent of protein degradation.The chilling process would affect the physiological and biochemical process in muscle,finally produce a significant impact on meat tenderness and other edible quality.Originally the normal chilling methods mainly include conventional chilling,rapid chilling(two stage chilling)and delay chilling.Different methods would affect the time-temperature-pH relations which is of great importance to meat tenderness.Good chilling procedure should allow muscle fibers entering into the rigor morits under smallest contraction state.Currently most of the enterprises in our country adopt conventional chilling,and some enterprises adopt the method of fast chilling.Rapid chilling can reduce the microbial growth and carcass dry,improving economic efficiency,but also easily producing cold contraction;delay chilling can effectively avoid this problem but it increases the risk of microbiological hazards.Therefore,considering both the economic benefit and meat quality,how to optimize and improve the chilling methods is a significant problem to study.The purpose of this study is to research on stepwise chilling,which is chilling the carcass tempature to 12-18? in 0-4? chilling room,holding a period of time,and then make the muscle entering into rigor morits in 12-18?,after that transferring the muscle to 0-4? chilling house,and study the influence of chilling method on temperature,pH,tenderness and WHC of beef muscle.With the help of protein electrophoresis,matrix assisted laser desorption ionization time-of-flight mass spectrometry(MALDI-TOF-MS)and other biological technology,to analyze the difference of stepwise and conventional chilling on protein degradation,clarifying the mechanism of stepwise cooling on beef quality.This study would provid a theoretical basis for the optimization of chilling process in slaughtering enterprises.Through optimization of the lysis buffer,sample volume and isoelectric focusing parameters of extracting beef proteins for two-dimensional electrophoresis analysis,we got the best separation conditions which were 800 ug protein sample volume,1% DTT in the liquid,IEF proceduresr: 300 V,1h,1000 V,1h,Grd 4000 V,1h,10000 V,2.5h;Grd10000V focus to 80000V*h.In terms of beef quality,the decline rate of pH in the treatment group was significantly higher than that in the 24h(P < 0.05),but there was no significant difference between their ultimate pH values(P > 0.05).Besides,the shear force values of the stepwise chilling group were significantly lower than that of conventional chilling treatment group after 1,7 and 14 days aging(P < 0.05).But there was no significant difference in terms of storage loss and cooking loss(P > 0.05).23 kinds of soluble protein were detected as differential abundant proteins in two treatments,among them 11 kinds was up-regulated in the stepwise chilling group while 12 kinds down-regulated.Through the GO and Pathway analysis,we found that the detected proteins involved in glycolysis and energy metabolism(phosphoglycerate mutase,malate dehydrogenase,pyruvate dehydrogenase,adenosine kinase,adenylate kinase),anti-oxidation stress(peroxide enzymes,glutathione-s-transfer enzyme and heat shock protein and alpha-aminoadipic semialdehyde dehydrogenase,acireductone dioxygenase)and myofibrillar composition protein(myosin binding protein and actin protein precursor),thus adjusting pH,ATP metabolism and reduced stress etc.,which would finally acting on meat quality.As for insoluble protein,27 kinds of differential abundant proteins were detected,including 16 up-regulated proteins and 11 down regulated ones.Through the GO and Pathway analysis,we found these proteins including the myofibrillar and cytoskeletal protein(troponin T and troponin C,actin,myosin,PDZ and LIM protein composition),myofibrillar structure maintaining protein(alpha crystallin protein,ankyrin and three domain protein 72 chaperone protein),in addition we also detected a variety of glycolysis and energy metabolism enzyme,such as 2,3-bisphosphoglycerate mutase enzyme,dihydrolipoamide dehydrogenase,creatine kinase and ubiquinol cytochrome C reductase etc..Stepwise chilling improved meat quality by mediating the expression of these proteins.