Effects Of Protein Nitrosylation On Beef Quality During Postmortem Aging

As a signal molecule widely existing in the skeletal muscles,nitric oxide(NO)generates depending on nitric oxide synthase(NOS).NO and NO-induced protein S-nitrosylation could be involved in diverse physiological processes through affecting protein structure and function,including calcium homeostasis and glucose uptaking.Beef muscles have a long duration of NOS activity during postmortem aging.Therefore,NO could possibly affect meat quality during postmortem aging,while few study has been published in this area.Thus,the objective of this study was to investigate the effect of protein nitrosylation on beef quality during postmortem aging,and explore the possible mechanism through treating beef with nitric oxide donor(GSNO)and NOS inhibitor(L-NAME).There are three parts of current study:1.Effects of protein nitrosylation on beef quality during postmortem agingThe aim of current study was to evaluate NO and its induced protein nitrosylation on beef quality.The 200 ?M GSNO(dissolved in normal saline)and 0.1 M L-NAME(dissolved in normal saline)were used to mange the level of NO in beef.After incubation for 24 h,the beef samples were vacuum-packaged and aged at 4? for 1,4,and 7 days.Experiments were performed to detect SNO level,final pH,beef color,tenderness and water holding capacity.Results showed that GSNO-treated group presented higher SNO level and lower tendermess at day 7 postmortem when compared with control group(P<0.05).L-NAME-treated group presented lower SNO level,L*values and water holding capacity,meanwhile greater tendermess at day 4 and 7 postmortem(P<0.05).These data suggest that NO and protein nitrosylation could downregulate beef tenderness during postmortem aging.2.Effects of protein nitrosylation on protein oxidation of beef during postmortem agingThe aim of current study was to examine the NO and its induced protein nitrosylation on protein oxidation.Results showed that earbonyl contents were higher and sulfhydryl content was lower in GSNO treated group(P<0.05),while L-NAME treated group showed opposite tend.Besides,samples from L-NAME-treated group showed weakening M line,blurry A band and broken Z line at day 7 postmortem,which is corresponding with tenderness alteration in Chapter 1.These results suggest that protein nitxosylation could increase protein oxidation and denaturation.3.Effects of protein nitrosylation on ?-calpain autolysis and protein proteolysis of beef during postmortem agingTo further investigate the reason determining tenderness alteration,Beef samples were incubated with one of the following treatments for 24 h at 4oC:control group(normal saline),100,200 and 400 GSNO solubilized in normal saline or 0.05,0.10 and 0.15 M L-NAME solubilized in normal saline respectively.After incubation,the beef samples were vacuum-packaged and aged at 4? for 1,4,and 7 days.Results showed that GSNO decreased increased the extent of ?-calpain autolysis,degradation of desmin and troponin-T(P<0.05)While L-NAME increased the extent of ?-calpain autolysis and upregulated degradation of desmin and troponin-T(P<0.05).Moreover,0.10 M and 0.15 M L-NAME-treated group showed more degradation of MHC at day 7 postmortem(P<0.05).The above results suggest that protein nitrosylation could regulate ?-calpain autolysis and its proteolysis activity during postmortem aging in beef SM muscle,which contribute to alterations of tenderness and sarcomere in part 1 and 2.