Identification of angiotensin converting enzyme (ACE) inhibitory and antioxidant peptides derived from Pixian broad bean paste

Pixian broad bean paste (PBBP) is a well-known fermented condiment in China. Herein, the water-soluble peptide extracts of PBBP were isolated by two sequential separations, ultrafiltration and reverse-phase high performance liquid chromatography (RP-HPLC). Ultra-performance liquid chromatography quadrupole time-of-flight mass spectrometry (UPLC-Q-TOF-MS) analysis resulted in the identification of peptides. Four novel bioactive peptides: RGLSK, NKGPR, DNLLN, and TPCPPQ, were found firstly based on our knowledge. Among them, RGLSK showed the strongest ACE inhibitory activity with IC50 value of 87 μmol/L, and TPCPPQ exhibited the highest antioxidant capacity (ABTS•+ assay, 535 μmol TE/g, DPPH• assay, 62.62 %). The electrospray ionization with triple-quadrupole mass spectrometry (ESI-QQQ-MS) was developed for the quantitative analysis of these peptides. The molecular docking suggested that RGLSK formed hydrogen bonds with S1 active sites (Ala354, Tyr523, Glu384) and made coordinate bonds with Zn2+ (His383, Glu411) of ACE. This study showed that PBBP was a good source of bioactive peptides.