Health-promoting activities of ultra-filtered okara protein hydrolysates released by in vitro gastrointestinal digestion: identification of active peptide from soybean lipoxygenase

Okara, a major by-product of the soymilk industry, which is rich in proteins, could possibly release under physiological conditions potential bioactive peptides. Thus, an okara protein isolate was digested sequentially with pepsin and pancreatin for c.a. 4 h. On the basis of its relatively high degree of hydrolysis and antioxidant activities (power reduction and radical scavenging activity), the okara protein hydrolysates at the end of the in vitro digestion were fractionated by ultra-filtration and the obtained ultra-filtered fractions were further tested for angiotensin-converting enzyme inhibition and multifunctional antioxidant activities. In the < 1 kDa molecular weight cutoff ultra-fraction the amino acid sequence, TIIPLPV, of a peptide from soybean lipoxygenase-1 with a calculated mass 751.48 Da was identified using LC-ESI-MS/MS techniques. The hydrophobic amino acids present in this peptide, particularly Val at terminal position, could likely be associated with the relatively high health-promoting attributes tested. This study evidenced that the consumption of okara protein may exert health benefits on the basis of the bioavailability and bioactivity of the identified peptide.