The Study On Perparation Of Sesame Protein And Antioxidant Activity Of Enzymatic Hydrolysis

The cold pressed dehulled sesame cake was used as the raw material to prepareprotein isolates by alkaline extraction followed by acid precipitation. The effects of pHvalue, the ratio of liquid to solid, the temperature, the time and the extraction times onthe extraction rate of protein were analyzed through single factor experiments. Based onthe response surface methodology, the extraction conditions of sesame protein wereoptimized, and the optimum conditions were as follows: pH9.5, ratio of liquid to solid20.2, temperature63.3℃, time124.3min and1extraction times. The order of factorsinfluencing protein extraction yield were pH>temperature>time> ratio of liquid to solid.Under these conditions, the extraction rate of protein was73.12%. Then, the proteincontent and the yield of protein isolates precipitated at pH4.5were90.02%and29.82%respectively. Compared with the functional properties of soy protein isolate and casein,sesame protein isolate has high oil absorption; Its water absorption is higher than casein,but slightly lower than the soy protein isolate; Other sesame protein isolate also hassome foaming capacity and emulsifying capacity.Five proteases of food grade, including Alealase, Papain, Neutrase, Flavorzymeand Protamex, were selected to hydrolysis sesame protein, and the degree of hydrolysis(DH) and1,1-diphenyl-2-picrylhydrazyl (DPPH) radical scavenging activities of theresulting hydrolysates were determined. The results showed that the hydrolysates ofAlcalase possess strong antioxidant potential than others, therefore, the Alcalase wasdetermined to be used to hydrolysis sesame protein for acquiring sesame proteinhydrolysates with high antioxidative activities. The optimal conditions for the enzymehydrolysis are as follows: pH9.0, temperature51.5℃, enzyme/substrate concentrationratio2.38%, substrate concentration3%, hydrolysis time3h. Under these conditions, theDPPH radical scavenging activity of the resulting sesame protein hydrolysates was74.68%and the degree of hydrolysis is21.26%.Sesame protein hydrolysates prepared as per the protocol in this study exhibitedantioxidant function in five different test models in vitro. The results show that the SPHexhibits the strong power of reduction ability and free radical scavenging capacity；Moreover, the SPH in certain concentration range shows a significant ability to inhibitlard’s autoxidation in lard oxidation system. The antioxidant activities of SPH were concentration dependent.Four highly specific endonuclease, including trypsin, chymotrypsin, clostridialprotease and V8protease, were selected to hydrolysis sesame protein. The results showthat the degree of hydrolysis gradually increases with the extension of enzymatic time.Where in the highest degree of hydrolysis is chymotrypsin, followed by clostridiumprotease, a degree of hydrolysis of trypsin and V8protease are relatively low. DPPHradical scavenging ability is measured in the same or similar degree of hydrolysis andthe antioxidant activity of four hydrolysates descending order is chymotrypsin, trypsin,clostridium protease and V8protease. The four enzymes hydrolyze different types ofamino acids, which leads to the different terminal amino acids of those peptides. Further,it affects the difference of the antioxidant activity of four hydrolysates. So it can be seenthat the terminal amino acid has a certain impact on the antioxidant activity of thepeptide.