Effects Of Of Hydroxyl Radical And Peroxy Radical Oxidation On The Structure And Gel Properties Of Duck Myofibrillar Protein

Myofibrillar protein（MP）is easily attacked by free radical and then undergoes oxidation reaction,which leads to changes in structure,functional properties and the properties of protein gels,ultimately affects the sensory quality and nutritional value of meat products.Protein oxidation is a covalent modification directly induced by reactive oxygen species or indirectly induced by oxidative stress by-products.Muscle contains transition metal ions,oxidase and heme,which can be used as precursors of reactive oxygen species to induce protein oxidation.Hydroxyl Radical（·OH）is the main active oxygen free radical that initiates protein oxidation and is ubiquitous in the process of meat postmortem,processing,storage and transportation.As the most powerful active oxygen metabolite in organism,it has active chemical properties and can oxidize numerous amino acid side chain radicals rapidly,which can change the conformation of protein.In addition,lipid oxidation products can also induce protein oxidation.Peroxy Radical（ROO·）is a representative free radical intermediate in lipid oxidation reaction,which can capture hydrogen atoms in protein and then initiate protein oxidation.At present,there are few studies on the influence of protein oxidation and lipid oxidation on the MP structure and gel properties of duck meat.Therefore,this paper used the hydroxyl radical generated by Fenton reaction to represent the ubiquitous free radicals in the processing of meat products and the peroxy free radical generated by the aerobic thermal decomposition of AAPH to represent lipid oxidation free radical,two simulated oxidation systems of hydroxyl free radical and peroxy free radical were established and applied to duck MP respectively to investigate the effects of different free radical oxidation on MP structure,thermal aggregation and gel properties of duck meat,Which provide theoretical basis for protein oxidation control in the processing and storage of meat and meat products.The main research contents and results are as follows:（1）Using hydroxyl free radical and peroxy free radical induced MP oxidation in duck meat to study the effects of hydroxyl free radical and peroxy free radical on the structure of MP.The results showed that both hydroxyl radical and peroxy radical oxidation can significantly change the structure of duck MP.The main manifestations were:·OH oxidation can significantly increase the carbonyl content of duck MP,Low concentration of ROO·oxidation（≤5 mmol/L AAPH）had no significant effect on the carbonyl content of MP（P>0.05）,while high oxidation（20 mmol/L AAPH）significantly increased the carbonyl content（P<0.05）,which indicated that the rate of MP carbonylation induced by·OH oxidation was higher and the reaction was more efficient.The sulfhydryl content,solubility and endogenous fluorescence intensity gradually decreased under the induction of free radical oxidation（P<0.05）,while the surface hydrophobicity increased significantly（P<0.05）.The interaction between ROO·and sulfhydryl was more intense,and·OH had a stronger oxidative induction effect on hydrophobic amino acids and tryptophan.free radical oxidation can also change the secondary structure of duck MP,the content ofα-helix andβ-turn decreased significantly（P<0.05）,and the content ofβ-sheets and random curls increased significantly（P<0.05）.The structure of duck MP changed from order to disorder,and·OH was more able to promote the change of order structure of duck MP.（2）Using hydroxyl free radical and peroxy free radical induced MP oxidation in duck meat to study the effects of hydroxyl free radicals and peroxy free radicals on the thermal aggregation behavior of MP.The results showed that both hydroxyl radical and peroxy radical oxidation can affect the thermal aggregation behavior of duck MP,The main manifestations were:low concentration of·OH oxidation had no obvious effect on the thermal stability of duck MP,while high oxidation significantly decreased the thermal stability of duck MP（P<0.05）,and the more enthalpy value decreased.the oxidation modification of ROO·significantly decreased the thermal stability of MP（P<0.05）,When the concentration of H₂O₂ and AAPH was 20 mmol/L,the thermal denaturation temperature of myosin was 51.88℃and 53.56℃,which indicated the oxidation induction of·OH on the thermal denaturation of myosin was stronger.The turbidity of duck meat MP gradually increased with the increase of temperature,when the temperature rised to 70℃,the turbidity began to decrease.the protein turbidity at the same temperature was proportional to the concentration of oxidant.The radical oxidation modification promoted the movement of protein in the direction of large particle size.the particle size increased at the beginning and then decreased with the increase of temperature,the particle size of the control group and the low-concentration oxidation group reached the maximum at 70℃,while high-concentration oxidation maked it denatured and aggregated to the maximum particle size at 60℃.With the increase of temperature,the absolute value of the Zeta potential of duck MP increased first and then decreased.When the concentration of H₂O₂and AAPH was 20 mmol/L,the absolute value of the potential reached the maximum at 60°C,which was 10℃earlier than the maximum temperature of the control group and low-concentration oxidation group,and the deeper the degree of oxidation was,the smaller the absolute value of Zeta potential was.The surface hydrophobicity of highly oxidized duck MP increased gradually at 30～50℃,and decreased significantly at 60～80℃（P<0.05）.the endogenous fluorescence intensity gradually decreased,and the red shift of the fluorescence peak became more obvious.The change trend of ROO·oxidation system is similar to that of·OH oxidation system.（3）Using hydroxyl free radical and peroxy free radical to induced MP oxidation in duck meat to study the effects of hydroxyl free radical and peroxy free radical on the properties of MP gel.The results showed that both hydroxyl radical and peroxy radical oxidation can change the gel properties of duck MP,slight oxidation had little effect on gel properties,while excessive oxidation significantly decreased gel properties（P<0.05）.The main manifestations were:·OH and ROO·oxidation decreased the whiteness of MP gel and increased the cooking loss,and the effects of the two radicals oxidation was not obvious.the hardness,elasticity and water retention of duck MP gel in the·OH oxidation system decreased more than that of ROO·oxidation system.free radical oxidation significantly increased the hydrophobic interaction content in the chemical force（P<0.05）,while the content of ionic bond and hydrogen bond decreased gradually,and hydrophobic interaction>ionic bond>hydrogen bond.the elastic modulus of the gel decreased significantly with the increase of oxidation degree（P<0.05）,and the peak temperature also advanced 4℃.the microstructure of the gel gradually became loose and rough under the oxidation modification of the free radical.