The Research In The Mechanism Of Apoptosis Occurrence On Yak Meat Quality And Microstructure Changes During Postmortem Aging

The tenderness is the main factor to decide the yak meat quality and grading,postmortem aging can effectively improve the yak meat eating quality especially tenderness. Besides the classical calcium activated enzyme tenderization theory, some scholars have found the occurrence of apoptosis induced by enzyme of Caspase cascade occurs, destroyed the functional and structural integrity of the cell. Because postmortem cut off the yak muscle main communication with the oxygen and external environment, therewith, skeletal muscle cell apoptosis. Postmortem tenderization process like cell apoptosis, so the theory is applied to the yak meat after postmortem tenderization mechanism will be a new field to the research, this research takes ten Datong yak Longissimus dorsi muscle(obtained randomly from Haiyan County,Qinghai province, China) as the research object, selects the front triceps(TB), central longissimus dorsi(ML), the rear of the semimembranosus(SM) as the experimental samples. Study on the postmortem yak meat in the changes in cell environmental factors, the apoptosis process, cell apoptosis factor and Caspase-3, 8, 9, the effect of Caspase-3 on the degradation of muscle fiber,the influence of apoptosis on yak meat quality and microstructure postmortem. Improvement of yak meat tenderness mechanism, in order to provide the theoretical basis of ensuring yak meat quality.This study includes six parts, the main conclusions are as follows:1.Changes in the cells environmental factors of yak meat postmortemThe different parts in yak meat Na+-K+-ATPase activity decreased significantly at24 h after slaughter(p<0.01), at 48 h postmortem, the Na+-K+-ATPase activity in TB decreased significantly(p<0.01), at 12 h postmortem, the Ca2+-ATPase activity in ML and SM reached a maximum, at 12 h postmortem, the Ca2+-ATPase activity in TB achieved the maximum value; at 24 h postmortem, the ATP content in TB and SM gradually stabilized, at 48 h postmortem, the ATP content in ML gradually stabilized.The p H value in yak meat postmortem increased first and decreased, then increased.The p H values in TB, ML, SM were found decreased to the minimum value at 48 h postmortem, the p H value to a minimum value at 48 h postmortem, so the cell environment factors of yak meat will be propitious to apoptosis occurred.2.The apoptotic process during yak meat postmortemPostmortem aging process destroys the structure of mitochondria in yak meat, at168 h postmortem, all mitochondrial almost began to collapse into a high electrondensity of the dot, and gradually gathered together, that the occurrence of apoptosis during yak meat postmortem aging. With the extension of the postmortem aging time in yak meat, inter cellular space increased gradually. Nuclear margination and apoptotic bodies formation. At the same time, increase the cell shrinkage, so the apoptosis occurred during postmortem aging time in yak meat. At 2h to 72 h postmortem, the number of apoptotic cell nuclear with a slow linear increase,increased quickly after 72 h postmortem, at 168 h postmortem, the number of apoptotic cell nuclear in TB and ML positive had extremely significant difference(p<0.01), so the apoptosis occurred during postmortem aging time in yak meat.3. the change of apoptosis factor and Caspase-3,-8,-9 protein expression in yak meat postmortem.Postmortem Caspase-3 degradation fragments of yak meat appeared at 17 k Da,the Caspase-3 activity of changed significantly, indicating that Caspase-3 participate in yak meat tenderness process postmortem; Caspase-9 degradation fragment appeared at 23 k Da, Caspase-9 activity and Caspase-3 activity was significantly correlated(p<0.001), that endogenous pathways initiated by Caspase-9 take part in the activation of Caspase-3; the degradation fragment of Caspase-8 18 k Da, the correlation analysis of Caspases-8 showed significant with Caspase-3(p<0.05),explain the hypoxia postmortem activated Caspase-8, and participate in the activation of Caspase-3. The above results showed that, the activation of Caspase-3 would be induced by cell apoptosis in yak meat postmortem.4.the Effect of Caspase-3 to myofibrillar protein degradation in yak meat postmortem agingAt 48 h Postmortem, the Troponin-T 30 k Da and desmin degradation products appeared in TB and SM DEVD group, and the that in ML appeared earlier than TB and SM, indicating that Caspase-3 was involved in the myofibrils degradation before48 h postmortem, further explained at the early postmortem, apoptosis guide the activation of Caspase-3 destroying myofibrils protein, taking part in yak meat tenderness.5.The effect of apoptosis on the yak meat quality during postmortem agingPressure loss and cooking loss and apoptosis rate were significantly correlated(p<0.05), the activity of Caspase-3 and the pressure loss was significantly correlated(p<0.01), cell apoptosis rate and L*, a*, b* were significantly correlated(p<0.05),Caspase-3 activity and L*, a*, b* all showed a significant correlation(p<0.01). MFIand apoptosis rate was significantly correlated(p<0.05); MFI and Caspase-3 activity showed a significant correlation(p<0.01), shear force values were significantly correlated with the apoptosis rate(p<0.001); hardness, adhesion and chewiness and apoptosis rate were significantly correlated(p<0.05) the activity of Caspase-3, only with elastic correlated significantly(p<0.05).6.the effect of apoptosis on the muscle yak muscle fiber ultrastructure during postmortem agingThe apoptosis rate and muscle fiber diameter, sarcomere length and inter cellular space showed a significant correlation(p<0.001), Caspase-3 activity and muscle fiber diameter, sarcomere length were significantly correlated(p<0.01), the activity of Caspase-3 and inter cellular space in ML and SM showed no significant correlation.To sum up, the apoptosis occurrence in yak meat during postmortem aging, and follow the deepening of apoptosis, mitochondrial membrane permeability change,inter cellular space increased, induced Caspase-3 activation, hydrolysis of muscle fiber protein, leading to loss of structural integrity in myofibrils, improved the yak meat tenderness, caused a certain impact on the color, water holding capacity and texture parameters.