Production and characterization of bioactive peptides from soy hydrolysate and soy-fermented food

Soy hydrolysate and the soy-fermented foods, natto and tempeh, were dephosphorylated, deglycosylated and digested with a variety of endoproteases (pronase, trypsin, Glu C protease, plasma proteases and kidney membrane proteases) to generate oligopeptides. The peptides were purified and characterized. They demonstrated a range of biological activities – angiotensin converting enzyme (ACE) inhibitory, anti-thrombotic, surface tension and antioxidant properties. The biologically active peptides were mostly derived from glycinin, a highly expressed soy protein, and were found mainly in the pronase, kidney membrane proteases and plasma proteases digests of the fermented foods. The proteases of lower specificity produced more oligopeptides and a higher percentage of bioactive peptides than the proteases of higher specificity, namely trypsin and Glu C. A peptide with ACE inhibitory activity was found in the pronase digest of natto, which also produced a peptide with surface active properties. The kidney membrane hydrolysate of natto contained an ACE inhibitor, in addition to a peptide with anti-thrombotic activity bearing homology to hirutonin, a previously described synthetic thrombin inhibitor [DiMaio, Gibbs, Lefebvre, & Munn, 1992, J. Med. Chem. 35, 3331]. Synthetic analogs were also evaluated as substrates for some inhibitors.