ANTIOXIDANT ACTIVITIES OF HYDROLYSATES ORIGINATED FROM SOYBEAN AND SOY MILK RESIDUE

Soybean (Glycine max) and soy milk residue (okara) are protein-rich materials. Soybean possesses the highest protein content among different types of beans (protein content of soybean varies from 40–42 %). Soy milk residue, a by-product of the soy milk manufacturing industry, contains approximately 27 % protein (by dry weight). A number of recent studies have investigated the improvement of functional properties of protein contained in soybean and okara by fermentation or by the use of proteolytic enzymes. The aim of this study was to evaluate the antioxidant activities of soybean and okara hydrolysates obtained by the fermentation with Aspergillus oryzae or by using proteolytic enzymes (neutrase and flavourzyme). DPPH radical scavenging assay was used to determine the antioxidant activities of hydrolysates. The concentration of peptides required to scavenge DPPH radical by 50 % (IC50 value) was used to evaluate the antioxidant activity of peptides produced obtained from hydrolysates. The results showed that when fermented with A. oryzae, the okara hydrolysate had higher antioxidant activity than the soybean hydrolysate, with IC50 values of 0.447 mg/ml and 3.95 mg/ml, respectively. The hydrolyzed okara obtained from hydrolysis using Neutrase had higher antioxidant activity than the one obtained from hydrolysis using Flavourzyme, with IC50 values of0.200 mg/ml and 0.407 mg/ml, respectively. Different peptide fractions obtained from the hydrolysates using cut-off membrane (10 kDa, 3 kDa and 1 kDa) possessed different antioxidant activities. The 1 kDa peptide fraction exhibited the highest antioxidant activity with an IC50 value of 0.158 mg/ml