Purification and identification of an ACE-inhibitory peptide from walnut protein hydrolysate

Angiotensin I-converting enzyme (ACE) is a dipeptidyl carboxypeptidase. It plays an important physiological role in regulating blood pressure in human bodies. ACE-inhibitory peptides inhibit the activity of ACE, thereby decreasing the tension of blood vessels and the blood volume, thus lowering blood pressure. ACE-inhibitory peptides derived from food proteins due to their safety properties and beneficial effects on human health have attracted more and more attentions on their ACE-inhibitory activity. In the present study, a novel ACE-inhibitory peptide, P-1a1, was homogeneously purified from walnut protein hydrolysate by ultrafiltration, consecutive column chromatography and high performance liquid chromatography. The purified peptide was characterized by Edman degradation, matrix-assisted laser desorption ionization time-of-flight mass spectrophotometer and a liquid-phase peptide sequencer. The amino acid sequence of P-1a1 was determined to be LPGRPPIKPWPL. The potent ACE-inhibitory peptide showed a high ACE-inhibitory activity with the IC50 value of 128.98 mu g/mL (95.2 mu mol/L). The purified peptide could be used in functional food products as a bioactive component with good ACE-inhibitory activity.