Study On The Preparation And Antioxidant Activity Of Black-Soybean Peptides

Black soybean contains approximately45%protein and is a potential source ofplant protein. The black soybean protein, in its original form, has some unknownbioactive peptides, which upon enzymatic hydrolysis will liberate a number of them.A series of researches have showed that not enough amounts of bioactive peptides areavailable in our daily diet. As the result it is necessary to study and prepare thebioactive peptides needed by humans. In this dissertation, a method of preparation ofblack soybean protein hydrolysates (BSPs), and the antioxidative activity of BSPshave been researched，which would provide the theoretical foundations for theutilization of BSPs.Initially, the preparation conditions of BSPs were studied. Different proteaseswere used to hydrolyze Black-soybean protein, according to the protein hydrolysisdegree (DH). Alcalase protease was selected as the most appropriate enzyme.Ultrasound pretreatment was applied to the Alcalase protease hydrolysis ofBlack-soybean protein. In the single-factors analysis, the influences of the ultrasoundtime, power, substrate concentration, pH, temperature and enzyme concentration onthe protein hydrolysis degree were studied. The DPPH· scavenging activity of theproducts was also compared. The response surface analysis were used to optimize thecondition of enzyme hydrolysis. The results showed that the optimum condition forpreparing black-soybean peptides with high-DPPH· scavenging activity were:ultrasound power1000w, ultrasound20min, pH8.64,substrate concentration4.00%,enzyme concentration4.00%, temperature50℃, enzyme hydrolysis time is4h. Underthis condition, the DPPH· scavenging activity of the peptides obtained is86.37±0.23%. In this dissertation, the antioxidant properties of BSPs are evaluatedusing different antioxidant tests in vitro; and the obtained enzyme hydrolysatesprovided strong antioxidant activity．In order to explore the correlation between different components of blacksoybean protein hydrolysate and their antioxidant activities from molecular weight,ultrafiltration was utilized to separate the peptides and then the capability of reducingability, the scavenging activities of DPPH radical,·OH radical and superoxide anion radical were determined．The comparison of the antioxidation capability of five blacksoybean peptides (BSP) indicated that the fifth one had the best antioxidation capacityin vitro. Finally molecular weight distribution of the hydrolysate was analyzed by thehigh performance liquid chromatography．The range of molecular weight distributewas between300Da-500Da．The area of those peptides was higher than50%of thetotal peptide areas. The composition of amino acids in those peptides is mostly Asp、Glu、Arg and Leu.