Angiotensin-I converting enzyme (ACE) inhibitory tripeptides from rice protein hydrolysate: Purification and characterization

In this study, angiotensin-I converting enzyme (ACE) inhibitory tripeptides from rice protein hydrolysate were purified and their properties were further characterized. Val-Asn-Pro (VNP) and Val-Trp-Pro (VWP) were successfully purified from rice protein hydrolysate through multi-step isolation and purification comprising of ultrafiltration and DA201-C macroporous adsorption resin, followed by a two-step reverse phase high performance liquid chromatography (RP-HPLC). The sequences of tripeptides were separately assayed by using automated protein/peptide sequencer. In addition, the stability of the tripeptides against ACE and simulated gastrointestinal proteases, ACE-inhibitory kinetics, and their antihypertensive effects in vivo were evaluated. Our results showed that VNP (IC50 value of 6.4 μM) and VWP (IC50 value of 4.5 μM) were both competitive ACE inhibitors, and stability against ACE and gastrointestinal proteases of pepsin and chymotrypsin. Furthermore, single oral administration of the tripeptides VNP and VWP at 5 mg/kg body weight in spontaneously hypertensive rats (SHRs) significantly decreased the systolic blood pressure (SBP) of 29 and 38 mmHg (P < 0.05), respectively, and the antihypertensive effects of tripeptides could last for 8 h minimally. The identified unique characterization of VNP and VWP may enable the application of rice protein hydrolysate as functional foods or pharmaceuticals against hypertension.