Okara (tofu dregs) is a soybean waste product from the tofu and soymilk processing industry. To create a useful product, the remaining protein content in okara must be used. The goal of this study was to determine the enzyme-substrate (E/S) ratio capable of producing the highest antioxidant activity from okara protein hydrolysate, as well as the amino acid composition of such a protein hydrolysate (especially the amino acid potential as antioxidants). To produce protein concentrate, the protein of okara was isolated using an alkaline extraction method followed by isoelectric precipitation. The protein concentrate was then hydrolyzed for six hours with papain enzyme at 50-55 °C and pH 7, with E/S ratios of 3%, 4%, 5%, 6%, and 7%. Using the DPPH method, the antioxidant activity of the obtained okara protein hydrolysate was determined. The HPLC method was used to determine the amino acid composition of the protein hydrolysate. The E/S ratio of 4% had the highest antioxidant activity (98.86%); the composition of amino acids L-Phenylalanine, L-Isoleucine, L-Valine, L-Glycine, L-Lysine, L-Tyrosine, L-Proline, L-Histidine, L-Cysteine and L-Methionine potentially contributed to the antioxidant activity effect. These findings suggest that okara protein hydrolysate has the potential to be used as an antioxidant-rich food ingredient.
Keywords: antioxidant, okara, protein hydrolysate, amino acid