The present study was conducted to investigate the effects of methyl jasmonate (MeJA) dipping treatment on mitochondrial energy metabolism and quality parameters of Nanguo pears during room temperature storage.  The results showed that MeJA treatment suppressed the respiration rate and weight loss, and maintained the flesh firmness of Nanguo pears.  MeJA also effectively maintained the content of ascorbic acid and titratable acidity in the fruit.  Furthermore, the activities of H⁺-ATPase, Ca²⁺-ATPase, succinate dehydrogenase (SDH) and cytochrome C oxidase (CCO) of the MeJA-treated fruit were significantly higher than those of the untreated fruit.  The contents of adenosine triphosphate (ATP) and adenosine diphosphate (ADP) and the energy charge were also enhanced by MeJA treatment.  These results suggest that postharvest MeJA treatment could maintain the quality of Nanguo pears, in part by modulating mitochondrial energy metabolism during room temperature storage.

 

This study aimed to examine changes in phosphorylation of sarcoplasmic and myofibrillar proteins from longissimus lumborum, semitendinosus, and psoas major muscles during postmortem ageing for 5 d.  These sarcoplasmic and myofibrillar proteins were separated using sodium dodecyl sulfate-polyacrylamide gel electrophoresis and stained with phosphorous and protein specific stains.  Myofibril fragmentation index, pH, the content of lactic acid and the relative activity of μ-calpain in three ovine muscles were measured.  These results showed that the relative phosphorylation level of sarcoplasmic and myofibrillar proteins of psoas major muscle were lower compared with longissimus lumborum and semitendinosus muscles (P<0.05).  The pH of psoas major muscle was the lowest at 0.5 h postmortem, and the highest after 12 h postmortem (P<0.05).  In addition, the relative activity of μ-calpain was higher within 5 d postmortem and myofibril fragmentation index was higher after 1 d postmortem in psoas major muscle than those of longissimus lumborum and semitendinosus muscles (P<0.05).  The sarcoplasmic protein phosphorylation may regulate the rate of pH decline to influence the μ-calpain activity and then proteolysis of proteins consequently.  This study gives a new perspective of the mechanism of postmortem meat tenderization.