Study On The Mechanism Of Very Fast Chilling In Early Postmortem Regulating Meat Tenderness

Chilling was an inevitable process in chilled meat processing.There are a series of chilling methods in actual production,and different chilling methods have different effects on meat quality.Very fast chilling had a group of advantages including rapidly reducing the temperature of livestock and poultry meat in a short time,reducing chilling loss,delaying the physiological and biochemical process after slaughtering,and effectively reducing the proliferation of microorganisms on the surface of livestock and poultry meat.However,results from existing studies about the effect of very fast chilling on tenderness were inconsistent.The reason is that the mechanism of how very fast chilling influences the tenderness of meat is unclear,which limits the application of very fast chilling technology in a certain extent.In this study,hot deboned fresh meat after slaughter was used as the research object,the tenderization effect of very fast chilling was verified on different cuts of lamb and different livestock and poultry meat,and the effect of very fast chilling at different chilling rates on the quality of fresh meat was analyzed.On glycolysis and actomyosin dissociation,calpain activity and skeletal protein degradation,and proteomics,the mechanism of very fast chilling regulating the tenderness of fresh meat was explored.It provides a theoretical basis and data support for the industrial application of very fast chilling.The specific research results are as follows:(1)Combined with the commercial production conditions in the abattoir,the tenderization effect of very fast chilling on different cuts of lamb,beef,pork and duck has been verified.The results showed that very fast chilling treatment delayed the decline rate of pH,but did not affect the ultimate pH of different livestock,poultry and cut meat.The very fast chilling group with a chilling rate of 14.25～15.10 ℃/h did not occur cold shortening and rigor mortis,and the tenderness of samples was significantly improved.However,the tenderization effect of very fast chilling differed in different livestock and poultry meat.In general,the tenderization effect of very fast chilling on lamb and pork were significantly better than that on duck and beef.(2)Conventional chilling(chilling rate 1.94 ℃/h,end point temperature 2 ℃,chilling time 18 h)was used as the control group,and the color,water holding capacity,nucleotides,free amino acids,and volatile flavor compounds of fresh lamb meat treated with different very fast chilling(VFC-I group:chilling rate 12.19 ℃/h,end point temperature-1 ℃,chilling time 3 h 7 min;VFC-II group: chilling rate15.10 ℃/h,end point temperature-1℃,chilling time 2 h 31 min)were studied.The results showed that the color and cooking loss of fresh lamb in very fast chilling group were not significantly different from those in conventional chilling group.The very fast chilling treatment delayed the degradation of nucleotides and the formation of free amino acids and volatile flavor compounds,which kept the quality of fresh lamb meat.(3)The changes of myofibril structure,sarcomere length,ATP content,actomyosin ATPase activity and actomyosin dissociation degree under different chilling treatments were analyzed.The mechanism of how very fast chilling affects glycolysis and actomyosin dissociation was investigated.The results showed that,at 24 h postmortem,the ATP content in very fast chilling group was higher than those in conventional chilling group 98.39～132.26%(P < 0.05),the actomyosin ATPase activity was lower than those in conventional chilling group 13.70～22.81%(P < 0.05),and the degree of actomyosin dissociation was higher than those in conventional chilling group 44.44～55.56%(P < 0.05).This indicated that,very fast chilling treatment delayed glycolysis and promoted actomyosin dissociation,which improved meat tenderness.(4)The calcium ion concentration in sarcoplasm,activity of μ-calpain and the degradation of calpastatin,troponin T and desmin were analyzed under different chilling treatments.The mechanism of how very fast chilling affects the activity of calpain and skeletal protein degradation was studied.The results showed that compared with conventional chilling group,at 6 h postmortem,very fast chilling group had an increase of the calcium ion concentration in the sarcoplasm by 32.04～45.66%(P < 0.05).At 6-24 h postmortem,the activity of μ-calpain in very fast chilling group was higher than that in conventional chilling group,and the gray value of calpastatin,troponin T and desminin in very fast chilling group lowered than those in conventional chilling group by 50.94-85.11%,14.72-31.22%,23.53-33.16% respectively(P < 0.05).This indicated that very fast chilling treatment enhanced the activity ofμ-calpain and promoted the degradation of calpastatin and skeletal protein.(5)The DIA proteome differences were compared between the conventional chilling group and very fast chilling group with their significant differences of tenderness at 24 h postmortem.The proteomic mechanism by which very fast chilling affects fresh meat tenderness was investigated.The results showed that very fast chilling treatment down-regulated the expression of the glycolytic enzymes ALDOA and the glycolytic rate-limiting enzyme PKM,and slowed the glycolysis process.Very fast chilling treatment up-regulated the expression of m-calpain and proteasomes(PSMB4,PSMB6,PSMC5),resulting in the degradation of proteins involved in the formation of the cytoskeleton,thereby promoting meat tenderization.