Soy protein hydrolysis with microbial protease to improve antioxidant and functional properties

Soybean proteins are widely used as nutritional and functional food ingredients. This investigation evaluated through a 2(3) central composite design the effect of three variables (pH, temperature and enzyme/substrate (E/S) ratio) on the production of soy protein isolate (SPI) hydrolysates with a microbial protease. Soluble peptides, antioxidant activity, and foaming and emulsifying capabilities of the hydrolysates were analyzed. All variables, as well as their interactions, were significant for the soluble peptides content of SPI hydrolysates. Optimal conditions for obtaining soluble peptides were around 30-35 °C, pH 6.5-9.5, and E/S ratios of 1,650-6,300 U g(-1). SPI hydrolysates produced at 30-45 °C, pH 8.0-9.5, and E/S ratios of 4,000-8,000 U g(-1) showed higher capacity to scavenge the 2,2'-azino-bis-(3-ethylbenzothiazoline)-6-sulfonic acid (ABTS) radical. Models for soluble peptides and ABTS activity of hydrolysates were obtained. In the range studied, the variables had not significant influence on the ability of hydrolysates to scavenge the 2,2-diphenyl-1-picrylhydrazyl (DPPH) radical. SPI hydrolysates also presented reducing power and ability to chelate iron. Hydrolysis temperature was significant for the Fe(2+)-chelating ability of hydrolysates. Temperature of hydrolysis was significant for the foaming capacity of hydrolysates, with higher values observed at 45 °C and 8,000 U g(-1). For emulsifying capacity, only E/S ratio presented a significant effect. Temperature and E/S ratio appeared to be more significant variables influencing the properties of the SPI hydrolysates. The results of this study indicate that specific hydrolysis conditions should be selected to obtain SPI hydrolysates with preferred characteristics.