Hydrolysis And Coupled Plastein Reaction On The Antioxidant Properties Of Soybean Protein Hydrolysates

In the present study, the effects of plastein reaction modification and further hydrolysis of two soybean protein hydrolysates on their antioxidant properties in vitro were investigated.1. Alcalase 2.4L FG was used to hydrolyze soybean proteins. When the hydrolysis time was 6 hour, the prepared hydrolysates had the best antioxidant property with a degree of hydrolysis of 14.0% and scavenging activity on ABTS radical of 43.6%.2. Soybean protein hydrolysates prepared by alcalase were used as substrate to carry out alcalase-catalyzed plastein reaction. Response surface analysis was applied to select reaction conditions with the decreased amount of the free amino groups of the modified hydrolysates as a response. The optimized conditions were obtained as follow: the addition level of alcalase was 1037 U/g proteins, the concentration of the hydrolysates was 30%, and reaction temperature was 20oC. With these conditions, the extent of reaction and the antioxidant property of the modified soybean hydrolysates reached the maximum level when the reaction time was 6 h. Scavenging activity on DPPH radical, reducing power, scavenging activity on hydroxyl radical and scavenging activity on superoxide radical of three modified hydrolysates with different extent of reaction were investigated. It was shown that the increase of antioxidant properties of the modified hydrolysates was followed by the increase in the decreased amount of free amino groups of the modified hydrolysates.3. Soybean protein hydrolysates prepared by alcalase were used as substrate to carry out papain-catalyzed plastein reaction. Optimal conditions obtained by single factor trials were as follow: the addition level of papain was 1 kU/g proteins, the concentration of the hydrolysates was 60%, and reaction temperature was 20oC. Under these conditions, when reaction time was increased from 1 to 8 h, the reaction system showed the occurrence of synthesis. The decreased amount of free amino groups of the modified hydrolysates was increased from 11.7μmol/g proteins to the maximum 15.7μmol/g proteins, then to 15.1μmol/g proteins. The antioxidant property of the modified hydrolysates exhibited a decrease trends first but after then to a fixed level.4. Papain was used to hydrolyze soybean proteins. When the hydrolysis time was 6 h, the prepared hydrolysates had the best antioxidant properties with a degree of hydrolysis of 8.96% and scavenging activity on ABTS radical of 43.5%.5. Soybean protein hydrolysates prepared by papain were used as substrate to carry out papain-catalyzed plastein reaction. Response surface analysis was aalso pplied to select reaction conditions. The optimized conditions were obtained as follow: the addition level of papain was 1 kU/g proteins, the concentration of the hydrolysates was 60%, and reaction temperature was 20oC. Three factors influenced the decreased amount of the free amino groups of the modified hydrolysates significantly, and the interactions between them were also significant. Under these conditions, when reaction time was increased from 1 to 8 h, the reaction system showed the occurrence of synthesis. A little increase in antioxidant properties of the modified hydrolysates was followed by the increase in the decreased amount of free amino groups of the modified hydrolysates. The maximal scavenging activity on ABTS radical of the hydrolysates modified was 46.9 % when plastein reaction time was 7 h.6. Soybean protein hydrolysates prepared by papain were used as substrate to carry out alcalase-catalyzed plastein reaction. Optimal conditions obtained by single factor trials were as follow: the addition level of alcalase was 1 kU/g proteins, the concentration of the hydrolysates was 60%, and reaction temperature was 20oC. Under these conditions, when reaction time was increased from 1 to 8 h, the reaction system showed the occurrence of hydrolysis. The increased amount of free amino groups of the modified hydrolysates reached the maximum 16.5±3.4μmol/g.when reaction time was 8 h. The antioxidant property of the modified hydrolysates was followed by the increase in the increased amount of free amino groups of the modified hydrolysates. The maximal scavenging activity on ABTS radical of the modified hydrolysates was 45.0% when reaction time was 8 h.7. Soybean protein hydrolysates were enzymatic hydrolyzed by different enzymes. The hydrolysates prepared by alcalase were further hydrolyzed by papain, or the hydrolysates prepared by papain were further hydrolyzed by alcalase. When the two hydrolysates were further hydrolyzed by another protease, the scavenging activity on ABTS radical of their final product were gradually decreased to a fixed level.