Soybean oligopeptides (SOP) with low molecular weights were prepared by two-step enzymatic hydrolysis on a pilot-scale. Peptide and free amino acid contents of SOP were 82.5 ± 1.13 % and 3.7 ± 0.28 % respectively. The molecular weight distribution of SOP was mainly bellow 1,000 Da (85.4 %), 56.7 % of which were 140-500 Da. SOP showed strong stability to proteolytic digestion by pepsin and trypsin. The antioxidant activities and in vitro and in vivo antihypertensive effects of SOP were evaluated. Results showed that SOP exhibited 1,1-diphenyl-2-picrylhydrazyl radical scavenging effect (IC50 = 4.5 ± 0.13 mg/mL), and significantly inhibited lipid peroxidation in linoleic acid oxidation system (IC50 = 1.2 ± 0.09 mg/mL). SOP had potent angiotensin I-converting enzyme inhibitory activity (IC50 = 1.1 ± 0.06 mg/mL), and antihypertensive effect in spontaneously hypertensive rats at a dose of 200 mg/kg. This study indicated that SOP could be a natural antioxidative or antihypertensive compound in the medicine and food industries.
Keywords: Antihypertensive activity; Antioxidant activity; Hydrolysates; Soybean.