Effect Of Endogenous Enzymes On The Formation Of Tenderness Of Yak Meat Under Different Oxidation Intensity During Postmortem Aging

Tenderness is considered to be one of the main factors affecting consumers'purchase intention.The processing and eating of yak meat are limited due to its thick fiber and poor tenderness.The limited degradation of myofibrillar protein?MP?by endogenous enzymes is the main reason for the improvement of tenderness during the postmortem aging.The oxidation of meat is very common during postmortem storage,protein oxidation will lead to the change of biochemical properties of MP and the decrease of endogenous enzyme activity,which will limit the degradation of MP,and eventually hinder the tenderization of meat after slaughter.It has been found that caspase and calpain are the main endogenous enzymes for improving meat tenderness during postmortem aging,but there is no report about the effect of endogenous enzymes on the formation of tenderness of yak meat during postmortem aging under different oxidation intensity.Therefore,six Gannan male yaks in Gansu Province were treated with different concentrations of H₂O₂?0,50,200 and 500 mmol/L?to simulate the natural postmortem aging of yak meat,and for aging 0,1,5,7 and 14 days,respectively.The change of content of ROS,carbonyl and total sulfhydryl,activity of endogenous enzymes?caspase-3,caspase-6 and calpain 1?,myofiber ultrastructure and MP degradation of yak meat were analyzed during postmortem aging.Combined with the iron-catalyzed oxidizing system?IOS?incubation model,the effects of different oxidation intensity on the activity of endogenous enzymes and the degradation of MP were studied.The main research results are as follows:?1?The results showed that the content of ROS and carbonyl increased,the content of total sulfhydryl decreased,the activity of caspase-3,caspase-6 and calpain-1 increased during0-1 day,and then increased during 1-14 day decreased;troponin-T and desmin were degraded to varying degrees,in which 200 and 500 mmol/L H₂O₂ treatment significantly inhibited the degradation of troponin-T and desmin?P<0.05?,and then inhibited the postmortem aging of yak meat.At the same aging time,with the increase of H₂O₂ concentration,the content of ROS and carbonyl increased significantly?P<0.05?,the content of total sulfhydryl decreased significantly?P<0.05?,the activity of caspase-3,caspase-6 and calpain-1 decreased significantly?P<0.05?,and then the degradation of troponin-T and desmin of yak meat were inhibited,especially 5-14 days weres significantly inhibited?P<0.05?.Protein oxidation hinders the improvement of tenderness of yak meat during postmortem aging,especially after5 days of postmortem aging.?2?In IOS,with the increase of oxidation intensity,the content of carbonyl,disulfide bond and dityrosine increased significantly?P<0.05?,and the content of total sulfhydryl and surface hydrophobicity decreased significantly?P<0.05?.Oxidation promoted the cross-linking of myosin heavy chain.At the same time,oxidation promoted 20-25 kDa myosin light chain degradation products.In addition,with the increase of oxidation intensity,the degradation of paramyosin,tropomyosin,actin and troponin-T occurred in varying degrees.?3?Hydroxyl radical oxidation significantly decreased the activity of caspase-3,caspase-6 and calpain 1?P<0.05?.MP oxidation enhanced the degradation of desmin by caspase-3and-6,but inhibited the degradation of troponin-T and desmin by calpain 1.MP of low concentration oxidation enhanced the degradation of troponin-T by caspase-3 and-6,while MP of high concentration oxidation decreased the degradation of troponin-T by calpain 1.Simultaneous oxidation of caspase-3,caspase-6,calpain 1 and MP reduced the degradation of troponin-T and desmin by endogenous enzymes?caspase-3,caspase-6,and calpain 1?.?4?In accordance with the results of in vitro oxidation test,the oxidation of yak meat protein during postmortem aging under different oxidation intensities will lead to the change of biochemical properties and the formation of cross-linking?mainly through disulfide bond and dityrosine,etc.?,strengthening the structure of myofibril.At the same time,the oxidation of endogenous enzymes?caspase-3,caspase-6 and calpain 1?decreased their activity during postmortem aging,which reduced the degradation of MP,and hindered the improvement of tenderness of yak meat during postmortem aging.