Production, optimisation and characterisation of angiotensin converting enzyme inhibitory peptides from sea cucumber (Stichopus japonicus) gonad

In this study, production of bioactive peptides with angiotensin converting enzyme (ACE) inhibitory activity from sea cucumber (Stichopus japonicus) gonad using commercial protamex was optimised by response surface methodology (RSM). As a result, the optimal condition to achieve the highest ACE inhibitory activity in sea cucumber gonad hydrolysate (SCGH) was hydrolysis for 1.95 h and E/S of 0.75%. For further characterisation, three individual peptides (EIYR, LF and NAPHMR) were purified and identified. The peptide NAPHMR showed the highest ACE inhibitory activity with IC50 of 260.22 +/- 3.71 mu M. NAPHMR was stable against simulated gastrointestinal digestion and revealed no significant cytotoxicity toward Caco-2 cells. Molecular docking study suggested that Arg, His and Asn residues in NAPHMR interact with the S2 pocket or Zn2+ binding motifs of ACE via hydrogen or pi-bonds, potentially contributing to ACE inhibitory effect. Sea cucumber gonad is thus a potential resource to produce ACE inhibitory peptides for preparation of functional foods.