Effect Of Mitochondrial Damage On Tenderization In Postmortem Beef Muscles

Tenderization of muscle after slaughter is a complex biochemical process.It is well documented that postmortem muscle dies in the form of apoptosis,and the apoptotic enzymes are activated earlier than other endogenous enzymes and play a major part in the early postmortem tenderization.Tenderization in postmortem is the result of the synergistic action of multiple endogenous enzymes.Previous studies have reported that mitochondria are damaged and significantly related to tenderness in postmortem.Cytochrome C in mitochondria is gradually released into the cytoplasm,and the mitochondrial pathway is the key pathway for apoptosis.As the first organelle stressed by postmortem stress environment,mitochondria are the decision-makers of cell apoptosis.The release of mitochondrial apoptotic factors directly determines the execution of the downstream apoptotic program and affects the postmortem tenderization process by regulating apoptotic enzymes.However,the regulatory mechanism is not clear.Therefore,the study will provide theoretical support for the establishment of new postmortem tenderization technology targeting mitochondria through the following research.The research contents and results are as follows:(1)Proteomic quantitative analysis of mitochondrial damage in posthumous beefThe samples of Longissimus dorsi(LT)of at 0 h and 24 h post-culturing was removed,and mitochondrial proteins were extracted.These proteins were reductively alkylated and enzymolyzed,labeled with TMT,one-dimensional separation with high p H RPLC,and detected by mass spectrometry to screen out the differential expression proteins(DEPs).The results showed that compared with 0 h,a total of 456 DEPs were differentially expressed within 24 h(P<0.05),14 have relatively high content and 442 have relatively low content.These differentially expressed proteins are mainly involved in mitochondrial respiratory chain complex and oxidative phosphorylation to cause mitochondrial damage and participate in tenderness changes through energy metabolism and cell apoptosis.In addition,we found that mitochondrial ribosomal proteins are involved in energy metabolism and apoptosis,HSPD1 and HSPE1 are involved in apoptosis,and physiological and morphological changes of mitochondria in the aging process,which may be potential proteins involved in mitochondrial oxidative stress and even affecting tenderness.Then PRM was used to validate some important proteins to make the data more reliable.(2)Analysis of mitochondrial injury and muscle fiber degradation in different parts of beefDifferent parts of beef have different muscle fiber types,which will affect the cell metabolism of postslaughter muscle to different degrees.Therefore,the most commonly used and representative LT,semitendinosus(ST),and psoas major(PM)were selected to detect myofibrillary degradation,mitochondrial damage and apoptotic enzyme activity.The results showed that there were differences between the tenderness and mitochondrial damage in the three parts of beef.Because the rate of glycolysis was different in three muscle parts,mitochondrial damage,caspase activation and myofibril degradation were different.The PM is a type I muscle fibers,with a higher rate of oxidative metabolism and lots of mitochondrial,so the changes of shape and structure of mitochondria and muscle fibers degradation were found in the early stage.Moreover,more apoptotic factors were released,indicating that mitochondrial damage and tenderness change occurred simultaneously.The more severe the damage,the better the tenderness.(3)The effect of Atractyloside on mitochondrial damage and myofibrillar degradationThe opening of mitochondrial membrane permeability conversion pore is a key factor in mitochondrial damage.Atractyloside can promote the opening of mitochondrial membrane permeability conversion pore,so we explore the influence of the opening of mitochondrial membrane permeability conversion pore on mitochondria-mediated apoptosis pathway by detecting myofibrillary degradation,mitochondrial damage,and apoptotic enzyme activity.The results showed that Atractyloside accelerated the damage of mitochondria during the postmortem by promoting the opening of the permeability transformation pore of mitochondria membrane,and the potential of mitochondria membrane was significantly lower than the control group.However,Atractyloside did not affect the content of cytoplasm Cytochrome c(Cyt-c)protein in the early stage of postmortem but increased the content of cytoplasm Cyt-c protein in the late stage of postmortem cytoplasm.However,the effect of treatment with Atractyloside on the activity of caspase-3 was not shown within 5 days after slaughter.As for the downstream myofibrillary proteins,atractyloside promotes the degradation of myosin in the early stage,and promotes the degradation of troponin-T at 120 h.This suggests that atractyloside may also affect the degradation of myofibrillin through other factors,which needs further research.