| Postmortem energy metabolism plays a crucial role in regulating meat quality.Numerous researches have stated the significant effects of postmortem activation of glycolysis and mitochondrial activities on meat quality,while the dynamic mechanism of conversion of energy metabolism and its regulatory role in meat quality remains unclear.Hence,the variations in internal environmental factors and microstructure,the content of energy metabolites,activities of energy metabolism enzymes,and transcriptomic data of longissimus dorsi muscles of Tan sheep during postmortem aging conditioning at 4℃ were investigated.Then the conversion mechanism of energy metabolic was revealed,the key factor regulating the conversion of energy metabolism was identified,the influence of the key factor on meat quality of Tan sheep was illustrated.The main results are as follows:(1)The variations in intramuscular environment factors and its effects on microstructure were investigated.Results indicated that the highest value of Na+-K+-ATPase was recorded as 613.89 U/L at day 1 postmortem,and the lowest value was observed as 331.97 U/L at day 8.The activity of Ca2+-ATPase significantly increased from 0 d to 1 d,and the maximum value recorded at 1 d as 215.05 IU/L.No significant changes in the content of DeoMb during 0-8 d was observed.The content of OxyMb was found to decrease significantly from 0 d to 8 d,while the content of MetMb was significantly increased.The content of HIF-1 increased significantly from day 0 to day 1,and peaked at day 1 due to the established state of hypoxia.The pH of muscle significantly decreased before 2 d and increased after 4 d,and the minimum value was recorded at 2 d.While aged for 8 d,the myofibrils were broken,the drip channels between myofibrils,between myofibril bundles,and between myofibrils and sarcolemma were formed,and Z lines were broken,and H bands were disappeared.The integrity of mitochondrial structure affected by the variations in the activities of ATPases,leading to the dissolution of outer membrane,inner membrane and matrix of mitochondria.(2)The variations in the activities of key enzymes and the content of energy metabolites were investigated.The activities of SDH,TPI,and COX decreased significantly from 0 d to 8 d.LDH activity increased before day 4 and peaked at day 4.Integrated analysis of activities of enzymes and abundance of energy metabolites showed that phosphocreatine metabolism led to the rapid consumption of phosphocreatine,resulting in the decrease of creatinine from 0 d to 4 d.The continuous decrease in activities of COX and SDH led to failure of aerobic metabolism,thus the content of adenosine,NADH and NADPH declined.Meanwhile,the failure of aerobic metabolism led to decrease in ATP levels,therefore the content of ADP and AMP declined.Postmortem glycolysis was activated in 4 days,which directly affected the variations in LDH and triggered the consumption of glycogen,glucose,phosphoenolpyruvate,and D-fructose-1,6-diphosphate,and the accumulation of lactate.(3)The changes of gene expression of Tan sheep muscles during postmortem aging were investigated based on next generation sequencing.The Q30 base percentage with a sequencing error rate of ≤0.1%was greater than 95.60%.Clean reads were sequentially compared with the Ovis aries genomic database,with match ratios ranging from 93.21%to 95.26%.Then,709 and 222 genes were identified as DEGs in Group 4/0 and 8/4,respectively(P<0.05).Among them,174 and 105 were upregulated DEGs,while 535 and 117 were down-regulated DEGs.A total of 19 DEGs were detected as common DEGs in Group 4/0 and 8/4.Then 19 DEGs were imported into the DEGs PPI network,including 18 nodes and 8 edges and 4 upregulated genes and 15 down-regulated genes.From 0 d to 4 d,transcriptional changes played an important role in the transition from aerobic to anaerobic metabolism,the activation of mitochondrial apoptotic pathways and the activation of proteolytic enzymes through translation and hydrogen transmembrane transported.Moreover,4 core genes(ATP6,COX2,COX1,and CYTB)were selected from the PPI network by MCODE.The 4 core genes interacted in multiple ways,including known and predicted regulations.Finally,6 target genes were selected for RT-qPCR analysis,and the results showed that the change trend of the expression of these target genes was basically consistent with the results of transcriptome sequencing,which confirmed the reliability of the transcriptome.(4)The core genes-differential energy metabolites interaction network was constructed and the key factors regulating energy metabolism were identified based on the integrated study of transcriptome and metabolomics.Mitochondrial genes COX1 and COX2 showed strong regulatory relationships with energy metabolites and other DEGs enriched in oxidative phosphorylation.Furthermore,COX was related to the hypoxia response of muscle cells.It was preliminarily considered that cytochrome c oxidase was the key regulator of conversion of energy metabolism during postmortem aging.(5)The important role of cytochrome c oxidase in energy metabolism and its effect on meat quality were clarified.It was found that dihydromyricetin significantly inhibit the activity of COX.COX affected the decrease of muscle pH by regulating glycolysis ability and the degradation of ATP.COX regulated the progression of apoptosis cascades by regulating mitochondrial Ca2+release.Overall,the transcription of COX subunits in muscle cells of Tan sheep significantly affected the activity of COX during postmortem aging,and participated in the regulation of postmortem energy metabolism by regulating oxidative phosphorylation,glycolysis and the degradation of ATP,and further affected the mitochondrial Ca2+ homeostasis,apoptosis cascades,and disintegration of mitochondrial structure,then affected the degradation of muscle structure,the content of NADH,and the decline of muscle pH,finally influenced the meat quality of Tan sheep.The purpose of this study was to provide theoretical guidance for controlling the aging process of Tan sheep meat. |
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