Study On Structure And Antioxidant Activity Of Whey Proteolysis-maillard Products After Oxidative Freeze-thaw

Whey protein is widely used in frozen foods such as desserts,ice cream,and meat products.Due to existence of complex pro-oxidative factors in food,in actual production and life,whey protein is often subjected to freezing and oxidation at the same time.There is only research on the single factor of oxidation or freezing.In this paper,the oxidation and freezing models of whey protein under different conditions are established by combining the two,and then the oxidized frozen and thawed whey protein is subjected to enzymatic hydrolysis and maillard modification.The changes of its structure and antioxidant activity were characterized by various means.Whey protein is oxidized and frozen in hydroxyl radical oxidation system,which is divided into three cases.The first case is to oxidize whey protein for 2 hours and 4 hours,and then freeze it at-18℃ and-40℃ for 2 days to 4 days.The second case is to freeze whey protein at-18℃ and-40℃ for 2 days to 4 days and then oxidize for 2 hours and 4hours.In the third case,whey protein was placed in the oxidation system at-18℃ and-40℃ for 2,4 and 6 freeze-thaw cycles.The results showed that: in the first case,the average particle size,turbidity and surface hydrophobicity index of whey protein were the largest after being oxidized for 2hours and then frozen at-18℃ for 2 days.In the second case,the carbonyl and free sulfhydryl content,average particle size and turbidity of whey protein that was frozen at-18°C for 4 days and then oxidized for 2 hours were the highest.In the third case,the free sulfhydryl content,average particle size and turbidity of whey protein were the largest after6 times of oxidative freeze-thaw cycles at-18℃,while the surface hydrophobicity,thermal weight loss and endogenous fluorescence intensity decreased the most,indicating that this treatment condition may have the most serious damage to structure of whey protein.Then whey protein in the third case was subjected to enzymatic hydrolysis,and it was found that the whey protein that was subjected to enzymatic hydrolysis at-18°C after 6times of oxidative freeze-thaw cycles had the highest antioxidant activity and absolute value of Zeta potential.At the same time,the endogenous fluorescence intensity and surface hydrophobicity decreased the most.Then,the maillard reaction was carried out with galactose and the enzymatic hydrolysis solution under the condition of ultrasonic heating.It was found that whey protein was subjected to enzymatic hydrolysis and maillard modification after 6 times of oxidative freeze-thaw cycles at-18°C,which had the smallest absolute value of Zeta potential,emulsion stability,endogenous fluorescence intensity and surface hydrophobicity,and the largest turbidity,comprehensive antioxidant activity and browning degree.The study established a model for structural changes of whey protein after oxidation and freezing under different conditions and conditions,and provided a theoretical reference for quality changes of foods supplemented with whey protein during storage,transportation and processing,and for innovative and efficient development of natural antioxidants provides ideas.