Red Bean Protein Hydrolysates And Its Antioxidant Peptides

Using alkaline protease, neutral protease and papain, in their respective suitable conditions, to hydrolyse red bean protein. Hydrolysates of the three enzymes were evaluated with hydrolysis degree, reducing power, antioxidation capacity of liposome, the capture ability of the superoxide radical and hydroxyl radical as an index. The results showed that, in case of alkaline protease, the red bean protein was hydrolyzed faster and the degree of hydrolysis was higher than the other two and can reach 22.39% in 4 h. And also the reducing power, anti-oxidation capacity of liposome, the capture abilities of the superoxide radical and hydroxyl radical were 0.222,63.84%,48.91%,49.63%.Single-factor tests, which including temperature, pH, substrate concentration, enzyme substrate ratio (E/S) and hydrolysis time, were used to the optimize the parameters of alkaline protease. Tests of antioxidant capacity of different degree of hydrolysis of hydrolysates were determined and the result showed that hydro lysate with the hydrolysis degree of 15% had the strongest antioxidant activity. Use Sephadex G-25 molecular size exclusion chromatography to determine the distribution of the molecular weight of different hydrolysis degree of red bean protein hydrolysates and the result showed that the higher the hydrolysis degree was, the smaller the average molecular weight would be.Under the foundation of the results of single-factor tests and the antioxidant activity of different hydrolysis degree of hydrolysates, used hydrolysis degree, reducing power, superoxide fadical scavenging ability and hydroxyl racical scavenging ability as the response value to build up an response surface methodology to optimize the process of bean protein hydrolysising by using alkaline protease. The optimum hydrolysis conditions were:substrate concentration was 2%(w/w), pH was 9.55, E/S was 2.72%, temperature was 52℃, time was 85 min. The optimized hydrolysate's reducing power, capture rate of superoxide fadical and capture rate of hydroxyl radical were 0.189,28.23% and 58.86, respectively, and the hydrolysis degree was 18.86% in this case.Molecular size exclusion chromatography was used to separate the red bean protein hydrolysate which was prepared by the optimal conditions. And the hydrolysate was separated into three components, which according to molecular weight from large to small were: componentⅠ, componentⅡand componentⅢ. Antioxidant tests showed that componentⅡhad the highest antioxidant activity.