Purification and characterization of angiotensin I-converting enzyme inhibitory peptides of small red bean (Phaseolus vulgaris) hydrolysates

• ACE inhibitory peptides were identified in small red bean proteins.
• A three-step purification process was used to fractionate ACE inhibitory peptides.
• A fraction with high ACE inhibitory activity demonstrated competitive inhibition.
• A novel ACE inhibitory peptide (PVNNPQIH) from phaseolin was identified.

Angiotensin I-converting enzyme (ACE) inhibitory activity was investigated for small red bean (Phaseolus vulgaris) protein hydrolysate produced by sequential digestion of Alcalase, papain followed by in vitro gastrointestinal simulation. The hydrolysate had ACE inhibitory activity with IC50 of 67.2 ± 1.8 μg protein/mL. Peptides responsible for potent ACE inhibitory activity were isolated by a three-step purification process, including ultrafiltration, gel filtration and preparative reverse phase high performance chromatography (RP-HPLC). The fraction obtained after RP-HPLC fractionation with the highest activity yielded an IC50 of 19.3 ± 1.4 μg protein/mL. Enzymatic kinetic studies using this fraction demonstrated competitive inhibition with Ki of 11.6 ± 1.7 μg protein/mL. Mass spectrometric characterization identified for the first time the octapeptide PVNNPQIH which demonstrated an IC50 value of 206.7 ± 3.9 μM. The results expand the knowledge base of ACE inhibitory properties of small red bean protein hydrolysate and should be useful in further identification of specific ACE inhibitory peptides in beans.