Optimizing of Enzyme Hydrolysis Condition for Bitterness Suppression of Soybean Protein Using Response Surface Methodology (RSM)

Enzyme hydrolysis of soybean protein can be adjusted according to purposes, but should be optimized for reaction time, concentration and substrate conditions to prevent bitterness caused by excessive hydrolysis. This study was carried out to find the optimal condition of the soybean protein hydrolysis process using a response surface methodology. The experiment was designed based on a central composite design, and the independent variables were the soybean protein extraction pH (X1, 10-12), enzyme concentration (X2, 0.1-0.5%) and hydrolysis time (X3, 150-210 minutes). The results of the degree of hydrolysis (Y1), pH (Y2) and soluble solid contents (Y3) were fitted to a response surface methodology model (R2= 0.91, 0.98, and 0.86, respectively). The optimal hydrolysis condition for soybean protein hydrolysis was as follows; pH 12, enzyme concentration 0.27% and 187.88 min, respectively. While richness and sourness were increased with soybean protein hydrolysis, the saltiness was decreased. The bitterness of the hydrolysate prepared at the optimal condition did not show any difference compared with that of the soybean protein, whereas richness and sourness showed a significant increase. The enzyme hydrolysate at the optimal condition showed distribution of a molecular weight lower than the soybean protein did to form intense bands at 35, and 25 kDa. Therefore, this hydrolysate was expected to be used as a high-value plant protein food material.