Preparation and Antioxidative Effects of Soybean Peptides*

In this work an alkaline protease, alcalase, was used to hydrolyze the separated soybean protein at 50 and pH 80. The dependence of hydrolysis time on hydrolysis degree and relative antioxidative activity was examined. The antioxidative activity of the hydrolysate reached the maximum after the hydrolysis for two hours, then decreased. The hydrolysate hydrolyzed for two hours was isolated on a Sephadex G25 column. The range of molecular weight for the collected fractions was 1001 300. A further purification of the isolated antioxidative peptides was conducted on a CMCellulose column. Two active peaks were observed. One of them was taken to investigate the antioxidative properties for in vitro model systems. It was found that the autoxidation rate of pyrogallol under the alkaline condition was decreased by, at least, 10%, indicating that some free radicals in the tested system were removed. In the experiment of the antihemolysis of erythrocyte, it was observed that the hemolysis degree of erythrocyte caused by hydroxyl free radicals was decreased obviously. This result indicates the protective effect of the antioxidative peptides on the cell membrane damage of erythrocyte. Moreover, it was also found that the membrane fluidity could be depressed after a solution of the antioxidative peptides was mixed with a liposome solution, indicating that the antioxidative peptides could further inhibit the membrane damage caused by lipid peroxidation when the small molecules of antioxidative peptides were embedded in liposome.