Effects Of Mitochondrial Apoptosis Signaling Pathway On Mitochondrial Damage And Meat Tenderness Of Tan Sheep During Postmortem Maturation

Tenderness is an important index to evaluate meat quality and affect consumers’ purchase desire,and postmortem ripening is an important way to improve muscle tenderness.In recent years,the process of Apoptosis was found to significantly improve muscle tenderness,which was widely studied and applied to explain the mechanism of postmortem muscle maturation and tender apoptosis.At present,the studies on the effect of apoptosis on muscle tenderness mainly focus on the degradation of myofibrillar protein by apoptosis enzyme(Caspase),while there are few reports on the mitochondrial signaling pathway during the maturation of Tan sheep meat after slaughter.In this study,the apoptosis inducing agent Lipopolysaccharide(LPS)was used to treat the longest muscle of Tan sheep after slaughter.The samples were collected at 0,6,12,24 and 72 h of maturation.The effects of cell apoptosis on the tenderness of Tan sheep meat were determined by pH,texture,shear force,Myofibril fragmentation index(MFI)and fragmentation index.The effects of LPS inducer on mitochondrial apoptosis signaling pathway were investigated through cell apoptosis rate,apoptotic enzyme activity,mitochondrial marker enzyme and mitochondrial apoptotic factor release.Cytochrome c(Cyt-c)redox status,mitochondrial damage degree and mitochondrial Ca2+concentration were used to investigate the influence of apoptosis on mitochondrial damage.Finally,correlation analysis was combined to analyze the influence of mitochondrial apoptosis signaling pathway on mitochondrial damage and tenderness of Tan sheep meat during postmortem maturation.The main research results are as follows:1.During postmortem maturation,the cooking loss rate and MFI showed an increasing trend;pH,elasticity and shear force values showed a decreasing trend;hardness,chewiness and cohesiveness showed an increasing and then decreasing trend;T22 peak area showed a decreasing trend with the extension of maturation time;and troponin-T degradation products gradually increased.The above results indicate that the structural changes of myogenic fibers during post-slaughter maturation shortened the molecular gap of muscle proteins,causing an increase in the water loss rate of muscles,making water retention poor,and at the same time promoting the process of myogenic fibrillation and myogenic fibrillar protein degradation leading to the improvement of the tenderness of Tan sheep.2.During postmortem maturation,the apoptosis rate of muscle cells of Tan sheep in control group and LPS induced treatment group was significantly increased(P<0.05).The activities of Caspase-3 and Caspase-9 increased first and then decreased.After LPS treatment,the activities of Caspase-3 and Caspase-9 in skeletal muscle of Tan sheep were higher than those in control group at any time point.Mitochondrial ATP content was significantly decreased(P<0.05).The ratio of Bax to Bcl-2 showed a significant increasing trend(P<0.05).The expression level of Cyt-c in the control group and the treatment group was significantly increased at 12 h postmortem,and decreased at 24 h to 72 h in the LPS group.The content of Caspase-3 activated fragment protein in LPS treatment group was higher than that in control group.That is,the effect of LPS inducer on mitochondrial signaling pathway during postmortem maturation is through activating Caspase-9 and Caspase-3 activities,reducing the level of cell energy metabolism,thereby affecting the activities of SDH and CS,and promoting the release of Cyt-c.Increasing the ratio of Bax/Bcl-2 can induce cell apoptosis through mitochondrial signaling pathway.3.With the extension of postmortem maturation time,the degree of mitochondrial damage in muscle cells increased gradually,the oxidation level of intracytoplasmic Cyt-c increased gradually,the oxidative stress level of mitochondria intensified,and the accumulation of Ca2+in mitochondria continued.Based on the correlation analysis in the previous two chapters,it can be seen that the decrease of pH value during postmortem maturation leads to the acidification of the internal environment,the decrease of ATP content affects the normal physiological function of mitochondria,and the Ca2+overload in mitochondria increases the level of mitochondrial oxidative stress.It resulted in the opening of Mitochondrial permeability transition pore(MPTP)and mitochondrial mitochondrial membrane potential decreased and other mitochondrial damage occurred.Subsequently,the activity of apoptosis-initiating enzyme Caspase-9 in the mitochondrial pathway was activated,and apoptosis-related factors Cyt-c and Bax were released successively,thus activating the activity of downstream Caspase-3,destroying the integrity of the structure of myofibrillar fibers in the muscle cells,leading to the occurrence of mitochondrial apoptosis cascade reaction,which played a role in improving the tenderness of Tans sheep meat.