The angiotensin I converting enzyme (ACE) inhibitory activity of fermented blue mussel sauce (FBMS) was investigated. Blue mussels were fermented with 25% NaCl (w/w) at 20 degrees C for 6 months and the resultant mixture was passed through a 40-mesh sieve, desalted using an electrodialyzer and then lyophilized. The IC50 value of FBMS for ACE activity was 1.01 mg/ml. An ACE inhibitory peptide was purified from FBMS using Sephadex G-75 gel chromatography, SP-Sephadex C-25 ion exchange chromatography and reversed-phase high-performance liquid chromatography on a C-18 column. The IC50 value of purified ACE inhibitory peptide was 19.34 mu g/ml, and 10 amino acid residues of the N-terminal sequence was EVMAGNLYPG. The purified peptide was evaluated for antihypertensive effect in spontaneously hypertensive rats (SHR) following oral administration. Blood pressure significantly decreased after peptide ingestion. This result suggested that FBMS may have beneficial effects on hypertension. (c) 2005 Elsevier Ltd. All rights reserved.