Effects of enzyme-assisted extraction conditions and precipitation methods on yield and functional properties of protein hydrolysates isolated from defatted soybean cake (Glycine max (L.) Merr)

Abstract

This study was initiated to investigate effects of a commercial enzyme (Alcalase 2.5 L) and precipitation agents (Ammonium sulphate, ethanol) on yields and functional properties of protein hydrolysates isolated from soybean cake. The results showed that conducting extraction with 0.1% (v/w) Alcalase 2.5 L, at 55oC for 1 h gave the highest crude protein yield. The highest amount of proteins were isolated at 80% solvent concentration for both precipitation methods. However, the highest protein yield obtained by using the ethanol precipitation was 86.73 ± 4.07%, which was significantly higher (p < 0.05) than that achieved by the ammonium sulphate purification (31.62 ± 0.44%). Functional properties of protein hydrolysates precipitated by ethanol were superior to those purified by ammonium sulphate, with protein solubility (44.36 ± 2.28%), water binding capacity (1.79 ± 0.05 g water/g isolate), oil binding capacity (1.46 ± 0.06 g oil/g isolate). Emulsifying and foaming index of proteins were analyzed to be significantly affected by pH levels in this study. Enzymatic extraction using Alcalase 2.5 L combined with ethanol purification could be a potential approach to extract protein from soybean cake in food industry to produce supplements with high protein content and good functionalities.