Enzymatic hydrolysis of ethanol-insoluble proteins from royal jelly and identification of ACE inhibitory peptides

In order to develop a physiologically functional food material from Royal Jelly (RJ) proteins precipitated by ethanol, we tried to hydrolyze them using various proteases. As a result of 0.4 wt%-2 h Orientase ONS hydrolysis treatment of ethanol-insoluble RJ proteins at 50°C, a newly obtained hydrolysate exhibited strong angiotensin I-converting enzyme (ACE) inhibitory activity (IC₅₀: 0.082 mg/ml). Single-dose, oral administration of the hydrolysate (1 g/kg of rat weight) in 13-week spontaneously hypertensive rats resulted in a significant reduction in the systolic blood pressure of ca. 12 mmHg (P<0.05) at 2 and 6 h after administration. By performing gel permeation chromatography of the hydrolysate, followed by reversed phase HPLCs, eight ACE inhibitory peptides were isolated and identified. Trp-Val-Leu (IC₅₀: 32.4 μM) and Tyr-Tyr-Ser-Pro (IC₅₀: 1.3 μM) were identified from natural resources for the first time. Some of the ACE inhibitory peptides were derived from the RJ-glycoprotein. Consequently, ethanol-insoluble RJ protein is thought to be a good resource as an antihypertensive food material.