Study On Soybean Peptides And Their Bioactivities

Soybean contains as high as 40% protein with well-balanced amino acid composition. The study and utilization of soybean protein have been drawn scientists' much attention. Soybean peptides (SP) are compounds with small molecular weight obtained from hydrolysis of soybean protein. Studies showed that SP were superior to soybean protein in both nutritional value and physiological functions. The preparation physical and chemical properties and biological acitivities of SP from Soybean Protein Isolates were studied systematically in this paper. The main results were shown as follows:1. Preparation, properties and gradation of SPPhosphate buffer was employed to control pH during enzyme hydrolysis of soybean protein isolates. By the standards of scavenging percentage of hydrolysate to hydroxyl radicals and hydrolytic degree of soybean protein, it was found that the optimum conditions for papain and neutral protease ASI.398 were: pH=8.3, t=4h, [E]/[S](W/W)=4%,[S] (W/V) =5%, T=70 and pH=6.4, t=4h, [E]/[S] (W/W)=2%, [S] (W/V)=6%, T=40 , respectively. The molecular weights of SP obtained under these enzyme hydrolysis conditions were below 10000Dal after ultrafiltration, and they were tested to have high antioxidation effect.RP-HPLC assay showed that the amino acid composition of SP was similar to that of soybean protein. SP was highly water soluble through the total pH range with low viscosity and it was graded with Sephadex G-25 and 3 grades were isolated.2. Biological activities of SPThe inhibitory effect of SP on oxidation of lipids and the acitivity of lipoxygenase, the scavenging or quenching effect of SP on free radicals, and the influences of SP on the malonaldehyde (MDA) content in mice liver juice, liver mitochondria and liver red blood cell were studied. The results showed that SP can inhibit the auto-oxidation of lard and soybean oil at 60 and can inhibit the activity of lipoxygenase significantly; SP also had scavenging effect on hydroxylradicals generated by Fenton system with IC50 value 6.220 mg/ml, under the concentration range of 1 mg/ml-50mg/ml, the scavenging rate of SP to -OH increased strongly when the concentration of SP increased, the maximum scavenging rate was 85.4%. SP did not show pro-oxidation effect.SP can reduce the content of MDA generated by mice liver juice during warm-bathing and induced by Fe2+ or H2O2. SP can also greatly reduce the concentration of MDA in mice liver mitochondria and liver red blood cell.In dose of 200, 400, 800mg/kg-d, SP increased the weight of thymus and spleen of mice significantly, compared to control, the increasing rates were 23.1%, 43.5%, 51.4% and 25.1%, 31.5%, 32.2%, respectively. SP can improve the phagocytic function of peritoneal macrophage with concentration-effect relationship.SP significantly increased the concentration of muscle glycogen and liver glycogen of mice and the concentration-relationship was obvious. SP also reduced the weight of mice abdominal subcutaneous fat by 17.9%, 22.9% and 51.4% in dose of 200, 400, 800mg/kg.d compared to control.