In Vitro Antioxidant Activity And ACE Inhibitory Acting Of Walnut Peptides

In this study, Walnut protein was extracted from walnut cake, and the technology of hydrolyzing walnut protein with different proteases were optimized, then the inoxidizability of walnut polypeptide was investigated. At last, the ACE inhibitory peptides were obtained by the methods of ultra filtration and gel filtration chromatography.Results showed that:condition of extracting walnut protein from walnut cake was optimized by response surface analysis, and the best conditions are as follows:extraction temperature65℃, extraction time5hour, pH8.0and liquid-solid ratio1:12. Under these conditions, the theoretical extraction rate of the protein reached87.54%, and the actual value was86.32%which was very close to the theoretical value, so the theoretical extraction rate was confirmed.Determined by single factor and orthogonal experiments, optimized condition of hydrolysis process of alkaline protease, papain and pepsin were as follows:(1) alkaline protease:Hydrolysis temperature60℃, the solid-liquid ratio1:25, pH10.0, enzyme addition7%, and the hydrolysis time were2hours. The final degree of hydrolysis was27.6%.(2) Papain:Hydrolysis temperature50℃, solid to liquid ratio1:25, pH6.0, enzyme addition3%, and the hydrolysis time were4hours. The final degree of hydrolysis was15.63%.(3) Pepsin:hydrolysis temperature55℃, the solid to liquid ratio1:20, pH3.0, enzyme addition4%, and the hydrolysis time were4hours. And the final degree of hydrolysis was15.72%.The walnut protein hydrolysates of alkaline protease, papain and pepsin all have a certain degree of resistance to oxidation. But different degree of resistance to oxidation corresponds to different evaluation methods. Overall, the effect of walnut protein hydrolysate of pepsin is prominent compared with the other two in removing hydroxyl radicals and superoxide anion radicals. Its IC50of removing hydroxyl redicals was6.02mg/ml, and IC50of removing superoxide anion radical was7.52mg/ml. These three kinds of hydrolysate were approximately equal in the ability of removing DPPH·radical and reducing power. Especially pointed out:The IC50of these three kinds of hydrolysates were less than1mg/ml and the effect was very obviousACE inhibitory effect was showed in three kinds of crude extract of walnut protein hydrolysates. After separation by ultra filtration membrane, it was found that the three kinds of walnut protein hydrolysates of which molecular weight less than10000have relatively high ACE inhibition rate, which means that the main component of the ACE inhibitory activity showed in the parts with small molecular weight. It was also found that J5K, and W5K components had more prominent inhibitory effect after measuring the IC50values of each component. These two components were purified by gel filtration chromatography,5and3chromatographic peaks showed respectively. The ACE inhibition rate of each component was measured, and the highest group was W3in these8components.