Acid modification of proteins from soymilk residue (okara)

Protein was extracted from soy residue (okara) at alkaline pH, and was modified by mild acid treatments. The degree of deamidation and peptide bond hydrolysis ranged from 10 to 70% and 6 to 15%, respectively. Size exclusion gel filtration chromatography revealed that there was a progressive degradation of the okara protein. Solubility was increased markedly by the modification, while other functional properties such as emulsifying and foaming properties were also improved. The okara protein products have good essential amino acid profiles, and acid modification also increased the in vitro digestability and available lysine content of okara protein. The results indicate that changes in functional properties of okara protein by acid modification were attributed to changes in physicochemical properties such as decreases in molecular size, higher net titratable charge and surface hydrophobicity. The low solubility of okara protein makes it difficult to be incorporated into many food systems. Improved solubility and other functional properties by acid modification will enhance the utilization okara protein as food ingredient.