Effect Of Polyphenol/Ascorbic Acid On Non-Enzymatic Oxidation Of Porcine Myofibrillar Protein

Protein oxidation is inevitable in the processing and storage of meat products.Protein oxidation not only leads to the deterioration of sensory and texture characteristics of meat products,but also poses a threat to human health.Due to the destruction of the internal tissue structure of the meat products after slaughter,the content of free iron ions in the muscle tissues will gradually increase,and Fenton reaction with the hydrogen peroxide accumulated in the metabolic process produces excessive free radicals,which leads to the oxidative degeneration of proteins.In order to prevent the harm caused by protein oxidation,antioxidants are often added in meat processing to alleviate oxidation,and natural antioxidants such as polyphenols and ascorbic acid have gradually become substitutes for some synthetic antioxidants in food processing due to their effective antioxidant properties and safety.But studies have found that the properties of these natural antioxidants can change under certain conditions,particularly in the presence of transition metal ions,casting doubt on their effectiveness in preventing the oxidation of proteins in meat products.Therefore,by adding exogenous iron ions and hydrogen peroxide to simulate the tissue environment of post-slaughter meat products,this study explored the influence of polyphenols and ascorbic acid on the oxidation of pork myofibrillar protein mediated by non-enzymatic oxidation system（Fenton-type reaction）,and analyzed and discussed the relationship between their anti-oxidation and pro-oxidation properties and molecular structure.This study can provide new insights and references for the development and application of natural antioxidants and the quality control of meat products.The main research contents are as follows:（1）The effect of gallic acid,a representative phenolic compound,on protein oxidation was investigated in the myofibrillar protein oxidation model system mediated by Fenton oxidation system.By measuring carbonyl compounds,Schiff base,sulfhydryl and other protein oxidation indexes,it is found that gallic acid has a double effect on the protein oxidation mediated by Fenton type system,that is,low concentration promotes the formation of some protein oxidation products,such as carbonyl value and Schiff base content,while high concentration of gallic acid inhibits the formation of these products.It was also found that quinones,the oxidation products of gallic acid,would interact with some groups on proteins and affect the results of protein oxidation.In order to explore the mechanism of the effect of gallic acid on the oxidation of protein,the influence of gallic acid on the content of·OH in Fenton system was detected by TPA fluorescence method.The results show that the change trend of·OH content is consistent with that of the above protein oxidation indexes,and·OH has been proved to be an important factor affecting the carbonyl content in protein oxidation system.This suggests that gallic acid affects the degree of protein oxidation by regulating the content of·OH in the oxidation system.By testing the Fe²⁺production amount in the system,it is found that gallic acid can effectively reduce Fe³⁺and accelerate the rate-limiting step of Fenton reaction,thus significantly increasing the·OH content in the system.Quinones also play an important role in gallic acid reduction of Fe³⁺and promotion of·OH production.（2）According to the same steps above,the effect of ascorbic acid on the oxidation of pork myofibrillar protein mediated by Fenton oxidation system and its mechanism were analyzed.Similarly,ascorbic acid can also reduce Fe³⁺,and has a dose-dependent dual effect on the content of·OH in the system,that is,low concentration of ascorbic acid promotes the generation of·OH,while relatively high concentration of ascorbic acid reduces the content of·OH in the system.However,different from gallic acid,this trend is not reflected in the change of protein oxidation index.The addition of ascorbic acid aggravates the oxidation degree of myofibrillar protein in Fenton type system.This is related to the specific mechanism of protein oxidation site and oxidation activity of ascorbic acid’s oxidation products.（3）A series of structurally related compounds belonging to the same phenolic acids as gallic acids were selected to investigate the structural-activity relationship between the ability of phenolic acids to regulate the oxidation activity of Fenton-type reactions and their molecular structure.The experimental results show that the molecular structure containing pyrogallol,catechol and hydroquinone phenolic acid complex reducing iron ion,accelerate Fenton reaction rate is the most effective.The number of hydroxyl and methoxy groups on the benzene ring has a linear relationship with the antioxidant effect of phenolic acids.In conclusion,the number and location of hydroxyl and methoxy groups on the benzene ring of phenolic acids have important relationship with their anti-oxidation and pro-oxidation properties.