A novel ACE inhibitory peptide from Douchi hydrolysate: Stability, inhibition mechanism, and antihypertensive potential in spontaneously hypertensive rats

Angiotensin I-converting enzyme (ACE) regulates blood pressure through the renin-angiotensin system. Douchi, a traditional fermented soybean condiment, may have antihypertensive effects, but research on ACE inhibitory peptides from Douchi hydrolysates is limited. We hypothesized that enzymatic treatment could enhance ACE inhibitory peptide diversity and efficacy. We tested ten single enzymes and four combinations, finding pepsin-trypsin-chymotrypsin most effective. Hydrolysates were purified using Sephadex G-15 and reversed-phase HPLC, and peptides were identified via LC-MS/MS. Five peptides (LF, VVF, VGAW, GLFG, NGK) were identified, with VGAW as the most potent ACE inhibitor (IC50 46.6 ± 5.2 μM) showing excellent thermal and pH stability. Lineweaver-Burk plots confirmed competitive inhibition, and molecular docking revealed eight hydrogen bonds between VGAW and ACE. In hypertensive rats, VGAW significantly reduced blood pressure at 12.5, 25, and 50 mg/kg. These findings highlight Douchi as a source of ACE inhibitory peptides and suggest VGAW as a promising functional food ingredient. [Display omitted] •Douchi hydrolysate was identified as a source of ACE inhibitory peptides.•VGAW was a competitive ACE inhibitor with an IC50 of 46.6 ± 5.2 μM.•Oral administration of VGAW reduced systolic and diastolic blood pressure in SHRs.•VGAW formed eight hydrogen bonds with amino acids in ACE S1 and S2 pockets.