H₂O₂-induced Oxidative Stress On Pork Quality During Aging And Its Underlying Mechanism

Oxidative stress has been known as one of the important factors influencing the quality of pork during postmortem aging.After slaughtered,pig is in a state of ischemia and hypoxia,which stimulates the production of reactive oxygen species(ROS)in muscle cells.As the reducing capacity in muscle gradually decreases post-slaughter,it leads to an imbalance in redox homeostasis,causing oxidative stress in muscle cells.ROS are able to attack biological macromolecules(proteins,fats,DNA,etc.)to change their structure and function,among which free radical-induced protein oxidation can affect the biochemical metabolism process of postmortem muscle cells,and thus affect the formation of fresh meat quality.However,the impact and underlying mechanism of ROS induced by oxidative stress on meat quality during postmortem aging are still unknown.Therefore,this thesis was to investigate the effect of different ROS level in pork by using different concentrations of H2O2,flollowed by vacuum packaging for 1,4,and 7 d at 4℃ on meat quality,protein oxidation,antioxidant enzymes,calcium release,and muscle fiber structure.The aim of this study was to further elucidate the impact and underlying mechanism of oxidative stress on pork quality during postmortem aging.The main research were described as follows:1.Study on the effect of different concentrations of H2O2 on quality and fiber structure of pork during postmortem aging.The LT muscles of pork of pH≥5.8 and L*≤50 were selected at 1 h after slaughter,and then trimed and soaked into following four treatment groups:0.9%NaCl(set as control group),4 mM,20 mM,and 100 mM H2O2 solutions in 0.9%NaCl,respectively.After 2 h incubation,the meat was removed from solution and then vacuum packaged and stored at 4℃ for 1,4,and 7 d.Meat quallity,protein degradation and muscle microstructure were determined during the postmortem aging.The results showed that increased H2O2 concentration significantly reduced the pH and shear force of the pork LT muscle during 7 d of storage(P<0.05),while the water holding capacity(purge loss,centrifugation loss,cooking loss)of the LT significantly decreased with an increase in H2O2 concentration(P<0.05).As H2O2 concentration increased,the a*of pork gradually decreased,and the treatment groups of 20 mM H2O2 and 100 mM H2O2 showed a significant lower a*value than that of control groups(P<0.05).In addition,the b*value of pork gradually increased along with the increasing H2O2 concentration,and the control group and 4 mM H2O2 treatment groups were significantly lower than those of 20 mM H2O2 and 100 mM H2O2 treatment groups at 4,and 7 d of storage(P<0.05).H2O2 treatment increased the myofibril fragmentation index(MFI)of the LT,and the MFI value significantly increased with the increase of H2O2 concentration(P<0.05).At 7 d of postmortem storage,H2O2 increased the degree of desmin degradation,which was significantly increased with the increase of H2O2 concentration(P<0.05).The degraded band of troponin-T was significantly lower at 1 d than at 4 and 7 d of postmortem storage(P<0.05).The SEM images showed that a high concentration of H2O2 treatment caused the fiber structure with serve fiber damage and fiber gaps.The above results indicated that H2O2-induced oxidative stress had an significant impact on changes in pork quality during postmortem aging.2.Study on the effect of different concentrations of H2O2 on protein oxidation and the correlations with pork meat quality during postmortem aging process.In the previous chapter,LT of pork treated with different H2O2 concentrations was used as samples to determine protein oxidation.The results showed that the ROS content of pork was significantly increased with the increase of H2O2 concentration.The contents of protein carbonyl,dityrosine,and protein surface hydrophobicity of LT were presented with an upward trend with the increase of H2O2 concentration,while the sulfhydryl,protein solubility were showed with a downward trend with the increase of H2O2 concentration(P<0.05).Through the principal component analysis(PCA)and multiple linear regression analysis(MLR),the significant correlations were found between protein oxidation and pork quality.Among them,protein carbonyl content was significantly correlated with pork pH,centrifugation loss,and shear force.The total thiol groups significantly correlated positively with pH and shear force,while negatively with b*.ROS was significantly correlated with centrifugation loss and a*value.The above results indicated that ROS-induced protein oxidation was significantly correlated with pork quality.Protein oxidation induced by oxidative stress affected changes in pork quality,which supplied a theoretical support for deep understanding of quality development during postmortem aging of pork.3.Study on the effect of different H2O2 concentrations on antioxidant enzymes activities and calcium release in pork during postmortem aging.Samples from previous study were used for parameters detection.The results showed that SOD activity in the 4 mM H2O2 group was significantly higher compared to other groups at 1 d(P<0.05),and the enzyme activity of antioxidant enzymes CAT,GSH-Px,and T-AOC exhibited with a decreasing trend with the increase of H2O2 concentration.Among them,antioxidant enzymes activities in the 100 mM H2O2 group were significantly lower that those in other groups(P<0.05).At 1,4,and 7 d of storage,the relative expression level of protein DJ-1 gradually increased with the increase of H2O2 concentration(P<0.05).The degree of MPTP opening significantly increased with the increase of H2O2 concentration(P<0.05).As the H2O2 concentration increased,the concentration of sarcoplasmic calcium concentration also increased among which 100 mM H2O2 group significantly showed with significantly higher content than control group(P<0.05).The activity of Ca2+-ATPase was significantly increased(P<0.05),while the activity of Na+/K+-ATPase was presented with decreasing trend with the increase of H2O2 concentration.The above results indicated that oxidative stress induced by H2O2 affected the antioxidant enzymes activities and calcium release,which were known as important factors in participanting formation of meat quality during postmortem aging.