Comparison Of Meat Quality,Calpain System And Proteolysis Between Commercial Meishan And Duroc X Landrace X Yorkshire Crossbred Pork

Meishan pig is one of Chinese indigenous pig of Taihu breeds.In recent years,Meishan pork has become more and more popular in China market due to its unique flavor and relatively higher pigment concentration.Compared to three crossbred(Duroc x Landrace x Yorkshire)pork,Meishan pork is more tender,juicier and tastier and has better water holding capacity.Proteolysis of key structural proteins including desmin,nebulin and integrin could contribute to the variation of pork WHC during postmortem storage.The degree of protein degradation is largely determined by the calpain system including calpain-1 and its endogenous inhibitor calpastatin.Thus,the purpose of this study was to compare the mRNA expression and the activity of calpain system,protein proteolysis,pH values and WHC between commercial Meishan and Duroc x Landrace x Yorkshire(DLY)crossbred pork during postmortem aging and explore the behind mechanism of greater WHC in commercial of Meishan pork.The results are as follows:1.Comparison of meat quality between Meishan pork and crossbred porkTo compare meat quality between Meishan and crossbred pork,and explore possible factors contributing to the water holding capacity of two breeds,meat color,intramuscular content,pH values,shear force and water holding capacity(purge loss,centrifugation loss,cooking loss)were determined.Compared with DLY pork,Meishan pork presented lower L*values and greater a*values(P<0.05),higher intramuscular content and greater water holding capacity.Meishan pork presented higher pH values at 45 min postmortem.The results of LF-NMR T2 relaxation data showed that Meishan pork had higher area of T2b and less area of T22,indicating that Meishan pork holding higher immobilized water and less free water compared to DLY pork.2.Comparison of calpain system between Meishan and crossbred porkCalpain system is a major factor contributing to pork quality through regulating the levels of protein degradation.The aim of this experiment was to compare the activity and mRNA expression of calpain system between two breeds.Calpain system was purified through DEAE Sepharose fast flow.Activities of calpain-1,calpain-2,and calpastatin were determined by the substrate of casein.The mRNA expression of calpain-1,calpain-2 and calpastatin were analyzed by reverse transcription-polymerase chain reaction.The results showed that the mRNA expression level of calpain-1 was lower in Meishan pork compared to that from DLY pork.Calpain-1 activity and the ratio of calpain-1 to calpastatin activity were lower in Meishan pork compared to those from DLY pork samples.3.Comparison of calpain-1 autolysis and protein degradation during postmortem aging between two breedsThe aim of the experiment was to compare the protein degradation and calpain-1 autolysis during postmortem aging.The relationship among protein degradation,calpain-1 autolysis and WHC was further analyzed.The results showed that Meishan pork presented lower ratio of desmin degradation at 7 d and decreased integrin degradation at 3 d and 7 d compared to DLY pork.Meishan pork presented less level of protein degradation at 7 d postmortem aging which was consistent with calpain-1 activity at 45 postmortem.Additionally,significant difference was found in desmin and integrin degradation at 7 d postmortem aging between two breeds.WHC was significantly different at 1 d and no significant difference was detected at 7 d during postmortem aging.These data suggest protein degradation is effective to influence WHC of DLY pork during postmortem aging.However,the higher WHC of Meishan pork could not explained by protein degradation in the early stage of postmortem aging.