Soybean residue (okara) was found to have a function as angiotensin I-converting enzyme (ACE) inhibitor. In this study, the soybean residue was a kind of waste in soybean processing manufactory and was used to produce peptides by Papain-hydrolysis (from Papaya) or Bromelain-hydrolysis (from Pineapple). Bioactive peptides against ACE activity were focused and the potent bioactive peptides were separated by using molecular weight cut off and reverse-phase high-performance liquid chromatography (RP-HPLC) was used to assay the inhibitor activity of peptides. The function of peptide fractions was evaluated by the inhibitory activity against ACE.
In this study, conditions for preparing small peptides from soybean by using vegetable enzyme hydrolysis were established. It showed that incubation of soybean residue with Papain at 70°C for 5 hours and Bromelain at 50°C for 5 hours could obtain hydrolysates with the smallest peptides and the highest amount of peptides. The fraction of peptides from soybean residues hydrolysate was separated according to different molecular weights by using ultrafiltration membrane cut-off ranging from 3,000 Da to 50,000 Da and each fraction used to evaluate inhibitory activity against ACE by RP-HPLC method. It was found that the peptide fractions from Bromelain hydrolysis showed a higher ACE inhibitory activity than that from Papain hydrolysis. In this case, the peptide fraction with high inhibitory activity against ACE was presented in crude hydrolysate, and with sequential decrease in inhibitory activity was in small peptide fraction 10-30 kDa, 3-10 kDa, and < 3 kDa, respectively. In conclusion, Bromelain is a good choice for producing peptides from soybean residues to have good inhibitory activity against ACE due to it could produce more peptides from soybean residues with very low concentration of proteolysis enzyme.
