Purification and identification of an angiotensin I-converting enzyme inhibitory peptide from fermented soybean extract

Angiotensin I-converting enzyme (ACE), a dipeptidyl carboxypeptidase, plays an important physiological role in regulating blood pressure. ACE-inhibitory peptides derived from food proteins have potential pharmaceutical and human health uses. In this study, we prepared a fermented soybean extract (FSE) through a rapid fermentation at an elevated temperature to accelerate proteolytic hydrolysis and described purification procedures to discover potent ACE-inhibitory peptides from FSE. After 3 days of aging, FSE exhibited ACE-inhibitory activity with an IC50 value of 1.46 mg/mL. Purification of novel ACE-inhibitory peptides was carried out using ultrafiltration and consecutive chromatographic methods. A novel ACE-inhibitory peptide, with 66-fold increase in ACE-inhibitory activity compared to that of FSE, was isolated from FSE through a five-step purification procedure. The amino acid sequence of the purified ACE-inhibitory peptides was determined to be Leu-Val-Gln-Gly-Ser by Edman degradation method, and its IC50 value was 22 μg/mL (43.7 μM).