Evaluation Of Antioxidant Properties In Vitro of Plastein-Reaction-Stressed Soybean Protein Hydrolysate

Alcalase was used in the present study to carry out an enzymatic hydrolysis of soybean protein isolate and a plastein reaction of the prepared hydrolysate in vitro, aiming to investigate the influence of the plastein reaction on the antioxidant properties of the modified hydrolysate. Soybean protein hydrolysate was prepared in a degree of hydrolysis of 14.0%, exhibited a scavenging activity of 43.6% on ABTS radical in vitro, and thus was used as the substrate of the plastein reaction to prepare the plastein-reaction-stressed hydrolysate. Response surface methodology was applied to select suitable reaction conditions as follows: enzyme addition level 1037 U/g peptides, substrate concentration 29.7% (w/v), reaction temperature 20.3°C. The stressed hydrolysate showed the highest scavenging activity on ABTS radical (about 47.9%) or maximal reaction extent when reaction time was 6 h. Three stressed hydrolysates with different reaction extents were prepared and evaluated for other antioxidant activities. Compared to the original hydrolysate, the stressed hydrolysate with lower reaction extent exhibited a similar (P > 0.05) scavenging activity on DPPH (or superoxide) radical and reducing power, but a significant higher activity (P < 0.05) on hydroxyl radical. The stressed hydrolysate with the highest reaction extent behaved as these investigated antioxidant properties were significantly higher (P < 0.05) than the original hydrolysate except for scavenging activity on DPPH radical. The results of the present study highlight that the alcalase-catalyzed plastein reaction appears to be capable of improving antioxidant properties of soybean protein hydrolysate.