The Research On Tenderness Quality Regulation And Preservation Technique During Meat Postmortem Ageing

Tenderness and freshness are important indicators for measuring meat quality.During postmortem ageing,the degradation of myofibril and its skeleton protein by endogenous enzymes helps to improve meat tenderness.Apoptosis is also highly correlated with the tenderness of meat,but the mechanism of endoplasmic reticulum stress in meat postmortem ageing is still unclear.The ageing process of meat is usually carried out by refrigeration at4℃,so preservation of meat is a necessary condition for the completion of ageing.Moreover,the juice loss of meat during storage,and promotes the growth of microorganisms.Therefore,the research on preservation technology during ageing is crucial.In this study,the endoplasmic reticulum stress inducer tunicamycin and inhibitor4-phenylbutyric acid were used to explore the regulation of endoplasmic reticulum stress on tenderness,myofibril structure and endogenous enzymes during postmortem ageing.The mechanisms of postmortem tenderness were further explored by the detection of apoptosis and autophagic pathways.Meanwhile,whey protein isolate and chitosan were used as substrates,citric acid was added for cross-linking,andε-polylysine hydrochloride as bacterial inhibitor to prepare composite aerogels,which were optimized and characterized for meat preservation during postmortem ageing.The study contents and results are as follows:(1)Western blot analysis showed that tunicamycin significantly increased the expression of BiP,up-regulated IRE1,XBP1 and CHOP contents,and induced endoplasmic reticulum stress.The results were opposite after 4-phenylbutyric acid treatment,which verified the regulatory effect of tunicamycin and 4-phenylbutyric acid on endoplasmic reticulum stress during postmortem ageing.Tunicamycin promoted a significant decrease in shear force,which respectively decreased by 43.54%,29.15%,and 27.60%at 1,3,and 5days,compared with the control,and myofibril fragmentation index respectively increased by 25.93%and 16.02%at 1 and 3 days.4-Phenylbutyric acid increased shear force by28.15%,42.70%,and 33.74%at 1,3,and 5 days respectively,and myofibril fragmentation index increased by 21.03%and 12.53%at 1 and 5 days respectively.Western blot analysis and transmission electron microscopy revealed that endoplasmic reticulum stress increased degradation of myofibril skeletal protein desmin and disruption of the internal structure of myofibril during postmortem ageing of chicken and activatedμ-calpain and caspase-12,with opposite results for 4-phenylbutyric acid treatment.The positive effect of endoplasmic reticulum stress on meat tenderization during postmortem ageing was determined.(2)Expression of apoptosis and autophagy pathway-related factors were determined by western blot and real-time quantitative PCR.Endoplasmic reticulum stress promoted the expression of pro-apoptotic factors Bax and Bim,inhibited the expression of anti-apoptotic factor Bcl-x L,and up-regulated cytochrome-c gene expression in the cytoplasm during postmortem ageing,activating the mitochondrial pathway of apoptosis.Meanwhile,endoplasmic reticulum stress activated autophagy markers Beclin-1 and LC3II,suppressed negative regulators p62,PI3K and mTOR,and promoted autophagy onset.The mechanism of endoplasmic reticulum stress on the regulation of apoptosis and autophagy during postmortem ageing and the promotion of meat tenderization was demonstrated.(3)The effect of different contents of whey protein isolate(4%,5%,6%,7%,8%),chitosan(0.6%,0.8%,1.0%,1.2%,1.4%),citric acid(0.25%,0.5%,1.0%,2.0%,4.0%)andε-polylysine hydrochloride(0.5%,1.0%,1.5%,2.0%,2.5%)on water absorption,water vapor adsorption and mechanical strength was investigated by single-factor test,and the optimal ratio of 6%whey protein isolate,1.2%chitosan,2.0%citric acid,2.0%ε-polylysine hydrochloride was obtained.The addition of citric acid andε-polylysine hydrochloride could improve the microstructure and mechanical properties of the composite aerogel.The density of aerogel containε-polylysine hydrochloride was 82.7±6.4 mg/cm~3 with significant bacterial inhibition against S.aureus,Salmonella,E.coli and Listeria.(4)The composite aerogel was used as an absorbent pad for chicken meat during postmortem ageing for preservation.By measuring the physicochemical indexes of meat during preservation,it was found that the aerogel containε-polylysine hydrochloride could effectively absorb the exuded liquid from meat,improve the color of meat,siginificantly alleviate the elevation of pH,TVB-N and total bacterial colony,and play a role in preservation of meat during postmortem ageing.