Characteristics And Antioxidant Activities Of Glycosylation Products Derived From Whey Protein Isolate

Whey protein is a rich nutrition protein that contains a variety of essential amino acids. It was with wide source and cheap price. Whey protein has been applied in food industry widely for its good processing characteristics, but some bad properties limited its application area. Therefore, enhancing and improving functional characteristics of whey protein becomes a high topic for domestic and foreign scientists. Glycosylation reaction can improve emulsification, solubility, heat stability and other function characteristics of whey protein, and has no chemical reagent compared with chemical and enzymatic method. But there were less research reports on improving the antioxidant activity of whey protein by glycosylation method, and they lacked corresponding basic theory research. So clarifying antioxidant mechanism of the glycosylation is Top Priority. This study was to investigate characteristics of Maillard reaction and discuss relationship of structure and antioxidant activity of glycosylated whey protein, which would provide technical support for application of new antioxidant in food industry. Therefore, this study was to with high theoretical value and practical significance.whey protein isolated(WPI) and six common sugars (ribose, galactose, glucose, fructose, lactose, and inulin) were selected as raw materials. There were four contents in this study, including kinetic study on glycosylation of whey protein, reaction mechanism of glycosylation of WPI, comparative experiment about antioxidant activity of glycosylated WPI and functional properties. The main experiment results obtained were as follows.Kinetic study:(1) When the reaction temperature was higher, the pH of glycosylated WPI conjugates was lower, but browning intensity and antioxidative activities became stronger. Antioxidative activities of different kinds of glycosylated WPI conjugates showed different improvement extents. Among these conjugates, ribose-WPI had the strongest antioxidative activity, and orders of antioxidative activities of other conjugates were as follows:Galactose-WPI> Fructose-WPI> Glucose-WPI> Lactose-WPI> Inulin-WPI.(2) In the case of effects of mass ratio on glycosylated WPI conjugates, the pH of glycosylated WPI conjugates was higher and the browning intensity stronger when WPI contents increased. But the conjugates had the strongest reducing power and DPPH radical scavenging activity under the condition of mass ratio of one to one.(3) With initial pH of Maillard reaction increasing, the pH of WPI conjugates also increased gradually, but browning intensity increased obviously in stronger alkaline environment (pH>10). Reducing power of conjugates had similar change trends with browning intensity. However, DPPH free radical scavenging ability had a little decrease in initial pH11or12.(4) The pH of glycosylated WPI conjugates decreased significantly as the heating time increased up to5h.. Browning intensity, reducing power and DPPH free radical scavenging ability all increased when Maillard reaction time prolonged.In study of Maillard reaction mechanism, SDS-PAGE showed the content of WPI lessened gradually as a function of heating time. At the same time, the amount of new WPI aggregates increased with the heating time increasing. Ribose-WPI system produced the most WPI aggregates and inulin-WPI system had the least amount. Fluorescence analysis displayed that fluorescence intensity of ribose-WPI and galactose-WPI systems increased at first and then decreased with Maillard reaction time prolonged. But lactose-WPI and inulin-WPI systems increased in all heating process.In study of antioxidant comparative experiment, antioxidative activity of WPI conjugates increased with its concentration increased. The pH (pH5-10) of environment system had a little effect on reducing power of conjugates. DPPH free radical scavenging ability decreased rapidly in alkaline conditions, while ABTS free radical scavenging capacity showed positive correlation with change of pH. Reducing power and ABTS free radical scavenging capacity of ribose-WPI were higher than BHA and Vc. So it could be used as a potential antioxidant applied in food industry.In study of functional properties of WPI conjugates, glycosylation of WPI improved solubility property of WPI at pH5. WPI conjugates had good solubility in pH6-10. And surface hydrophobicity of WPI conjugates decreased constantly after0.5h of heating time.