Characterization and identification of angiotensin I-converting enzyme (ACE) inhibitory peptides derived from tilapia using Virgibacillus halodenitrificans SK1-3-7 proteinases

Angiotensin I-converting enzyme (ACE) inhibitory activity of tilapia mince (TM) hydrolyzed by Virgibacillus halodenitrificans SK1-3-7 proteinases with a 48% degree of hydrolysis showed the highest ACE inhibitory activity with an IC50 of 0.54 mg/mL. After ultrafiltration (UF) and chromatographic separation via anion exchange, cation exchange and size exclusion chromatography, the fraction with the highest ACE inhibitory activity with an IC50 of 0.15 mg/mL was obtained. The peptides showed uncompetitive inhibition characteristics with an inhibition constant (Ki) of 0.18 mg/mL. The peptides showed high thermostability at 100 and 121 °C, as well as pH stability at a wide pH range of 2-10, and also maintained ACE inhibitory activity after in vitro gastrointestinal digestion. The most potent novel ACE inhibitory peptide identified was MILLLFR with an IC50 of 0.12 µM. TM hydrolysate prepared by V. halodenitrificans SK1-3-7 proteinases could serve as a source of peptides with ACE inhibitory activity.