Studs On Mechanism Of Temperature PSE Pork Formation And Pork Quality Changes Postmortem In Summer

Heat stress is a major stress factor that induces PSE pork formation;thus,researchers came up with a number of ways to reduce PSE pork in heat stress conditions,such as pigsty cooling and antioxidants addition in the fodder.However,PSE pork still occurs in high temperature periods in summer,which causes considerable concern in the meat industry.Elucidation of the molecular mechanism of PSE pork formation in summer is critical to preventing it postmortem;hence,this study aims at probing the mechanism of PSE pork formation and pork quality changes within 24 hours postmortem in summer,based on a halothane gene recessive(HalNN)ternary hybrid commercial pig population Duroc×(Landrace×Large White).Transcriptomics and proteomics means combined with carcass trait,meat quality and energy metabolites analyses were used,so as to find the critical genes and proteins involved in PSE pork formation postmortem and subsequently elucidate the molecular mechanisms pertinent to meat quality changes within 24 hours postmortem.The main results are as follows:(1)There have been 10.23%on PSE pork incidence rate in summer,significantly higher than other seasons.Ten normal swine carcasses(with normal longissimus et lumborum,LL)and ten PSE swine carcasses(with PSE LL)were selected based on their pH values at 45 min postmortem;their carcass traits and halothane phenotype were characterized,and their meat quality and energy metabolism related enzyme activities in LL and semimembranosus(SM)were determined at 45 min,5 h,12 h and 24 h postmortem,respectively.It was found that the porcine halothane gene was all of the recessive homozygote(Halnn)type;hence genes other than halothane gene expression may be responsible for inducing PSE pork formation.The ocular muscle area and leg-to-boody ratio of PSE carcasses were significantly lower than that of normal carcasses(P<0.05).Within 24 hours postmortem,the tenderness and the color,especially the L*value,of PSE pork,was significantly lower than that of normal LL(P<0.05).At 45 min postmortem,SM of PSE carcasses did not show PSE pork characteristics.However,at 12 h and 24 h postmortem,SM of PSE carcasses showed significantly lower water-holding capacity than did SM of normal carcasses,and between 5 h and 24 h postmortem,SM of PSE carcasses had significantly lower tenderness than that of normal carcasses(P<0.05).At 45 min postmortem,LL of PSE pork exhibited significantly higher creatin kinase and glyceraldehyde-3-phosphate dehydrogenase yet lower hexokinase activities than did LL of normal pork(P<0.05);however,between 5 h to 24 h postmortem,PSE pork showed higher hexokinase activity than normal pork(P<0.05)than normal pork,and reduced lactic dehydrogenase activity in LL(P<0.05).It is deduced that glycolysis reaction in PSE pork postmortem was mainly promoted by rise in creatin kinase and glyceraldehyde-3-phosphate dehydrogenase activities,and sustained by rise in hexokinase activity.(2)Total RNA in SM and LL of both PSE and normal carcasses were extracted and then compared by using transcriptome technology to identify the differential expression of genes(DEG)and metabolic pathway.It was found that the DEG between experimental groups was enriched significantly in immune system related pathways(Q-value≤0.05),and the DEG between LL and SM are mainly related to muscle growth,immune regulation and cell apoptosis.RYR1 gene did not have significantly differential expression in LL between PSE and normal carcasses;however,it had up-regulated expression in SM of PSE carcasses.Genes possibly related to differences in LL meat quality between PSE and normal carcasses were screened out:HSPA6,FOXO6,FOS,XIRP1,PVALB,MYH4,MYLIP,FUT11,and PPP1R3B,and that possibly related to differences in LL and SM meat quality between PSE and normal carcasses were also screened out:ATF3,MS4A2,IER2,DUSP1,CSF1R,and EGR1.(3)Differential protein expression in PSE LL and normal LL at 45min and 24h postmortem were dug out by means of proteome technology,and the possible marker proteins were found affecting postmortem pork quality changes.The results indicate that lowered aerobic metabolism and elevated anaerobic metabolism in muscle cells may be a major reason for PSE pork generation.At 45h postmortem,PSE pork exhibited down-regulated proteins expression in the citrate cycle and oxidative phosphorylation cycle,including pyruvate dehydrogenase,cis-aconitase,isocitrate dehydrogenase,cytochrome C oxidase,cytochrome C reductase and NADH dehydrogenase,as well as up-regulated proteins expression in the glycolysis cycle,including glyceraldehyde-3-phosphate dehydrogenase,L-lactate dehydrogenase,and enolase.Besides,Hspβ7 and troponin C can also serve as marker proteins for PSE pork.The fact that PSE pork has lower tenderness than normal pork may be related to up-regulated expression of calcium/calmodulin-dependent protein kinase type II subunit delta and collagen alpha-1(XII)chain isoform X4 at 45 min and 24 h postmortem.(4)Correlation analysis was conducted of transcriptome and proteome for PSE and normal pork at 45 min postmortem in order to reveal the molecular regulation mechanism of PSE pork formation.Two genes,i.e.,LOC100736765 and PVALB,may be among the key genes and proteins that cause PSE pork formation;and the key proteins expressions regulated following gene transcription may be a key cause of PSE pork evolution.