Study On Effects Of Protein S-nitrosylation On Meat Quality And Energy Metabolism Of Postmortem Pork

The glycolysis plays a vital role during the coversion of muscle to meat after postmorterm aging which is closely related to the meat quality including color,water holding capacity and tendness.Reactive oxygen and nitrogen species could accumulate in pork muscles during postmortem aging.Nitrogen species,including nitric oxide produced by the catalysis of nitric oxide synthase,could react with sulfydryl of protein cysteine to form protein nitrosylation regulating protein structure and function.The aim of this research was to explore the effects of nitric oxide(NO)and its induced protein S-nitrosylation on the meat quality and energy metabolism of postmortem pork.1.Effects of protein S-nitrosylation on meat qualityThe aim of this chapter was to investigate the effects of NO on meat quality.The M.longissimus lumborum muscles within 45 min post slaughter from pork were incubated with control,nitric oxide synthase(NOS)inhibitor and NO donor group at 4? for 12 h.The muscle was then vacuum packaged and stored for 1 and 4 d at 4?.The L*and b*of NOS inhibitor treatment was notably higher than the control treatment and the NO donor group at 1 and 4 d(P<0.05).However there was no significant differences about a*among three treatments.The NOS inhibitor group significantly reduced the drip loss and purge loss,which is consistent with the result of nuclear magnetic resonance(NMR).In addition,the NOS inhibitor group significantly reduced the concentration of protein thiol and the protein solubility(P<0.05).These results indicate that inhibit NO generation could affect the color,reduce the water holding capacity,and reduce protein oxidation during the conversion of muscle to meat.2.Effects of protein S-nitrosylation on glycolysisThe aim of this chapter was to investigate the effects of NO on the glycogen metabolism of postmortem pork.The pork samples were incubated with control(0.9%NaCl),NOS inhibitor,or NO donor for 4 and 12 h at 4?.Results indicated that NOS inhibitor treatment resulted in significantly lower level of glycogen and higher lactate content at 24 h compared those of control and NO donor treatments(P<0.05).The pH from NOS inhibitor group was significantly lower compared to other treatments indicating the fast glycolysis during postmortem aging(P<0.05).In addition,the NOS inhibitor group could significantly increase ATP and IMP at 12 h and 24 h.The(AMP+IMP)/ATP ratio was also significantly higher than the control and NO donor group indicating that inhibiting the production of NO could accelerate the ATP synthesis and decomposition.3.Effects of protein S-nitrosylation on the activities of GP,GAPDH and PKBased on the results of second chapter,the aim of this chapter was to investigate the effects of NO on GP,GAPDH and PK of the glycolysis.The pork samples were incubated with control(0.9%NaCl),NOS inhibitor,or NO donor for 4 and 12 h at 4?.Results indicated that the activities of glyolytic enzymes including GP,GAPDH and PK were significantly different among three treatments possibly due to the different levels of protein S-nitrosylation(P<0.05).These results suggested that NO could regulate the glycogen metabolism through modulating the activities of glycolytic enzymes by protein S-nitrosylation.