Angiotensin I-converting enzyme inhibitor derived from soy protein hydrolysate and produced by using membrane reactor

Five different proteolytic enzymes, including Alcalase, Flavourzyme, trypsin, chymotrypsin and pepsin were employed to hydrolyze isolated soy protein (ISP) to produce the hydrolysates, respectively. The result indicated that hydrolysis of ISP for 0.5–6 h with Alcalase produced the highest ACE inhibitory activity. Therefore, Alcalase was selected for further study on optimization of hydrolysis conditions. The optimum conditions for Alcalase to hydrolyze ISP to produce the lowest IC50 value were: E/S = 0.01, hydrolysis temperature = 50 °C, pH 9.0 and hydrolysis time = 6 h. Under these conditions, the IC50 value of ISP was significantly reduced from 66.4 to 0.67 mg protein/ml. The lower IC50 value represented the higher the ACE inhibitory activity. Moreover, several membranes with molecular weight cut-offs (MWCFs) of 1000–30,000Da were used to filter the hydrolysate. The 10 kDa permeate obtained from the treatment of the hydrolysate by 10,000 Da MWCF membrane could further reduce its IC50 value from 0.668 to 0.078 mg protein/ml with a peptide recovery of 67.5%. An operation stability study showed that the membrane reactor system could maintain a steady production of ISP hydrolysate for over 8 h. The in vitro effect of gastrointestinal protease on ACE inhibitory activity of 10 kDa permeate was also investigated. The results suggested that gastrointestinal proteases have very little effect on the ACE inhibitory activity of 10 kDa permeate.