Purification and hypotensive activity of rapeseed protein-derived renin and angiotensin converting enzyme inhibitory peptides

Rapeseed protein isolate (RPI) was hydrolyzed with Alcalase followed by reverse-phase high performance liquid chromatography (RP-HPLC) purification of bioactive peptides. The rapeseed protein hydrolysate (RPH) obtained after 4 h digestion with Alcalase had a degree of hydrolysis (DH) of ～11%. Gel permeation chromatography separation showed high contents of low molecular weight peptides in the RPH when compared to the RPI. After preparative and analytical RP-HPLC separations, three peptides (LY, TF and RALP) were purified and amino acid sequence determined by tandem mass spectrometry. LY (IC₅₀, 0.11 mM) was the most potent (p < 0.05) against ACE activity when compared to TF (IC₅₀, 0.81 mM) and RALP (IC₅₀, 0.65 mM). However, RALP (IC₅₀, 0.97 mM) was the most potent (p < 0.05) against renin activity when compared to LY (IC₅₀, 1.87 mM) and TF (IC₅₀, 3.1 mM). Single oral administration (30 mg/kg body weight) to spontaneously hypertensive rats showed LY and RALP to be the more effective hypotensive agents with maximum blood pressure reduction of ?26 and 16 mmHg, respectively when compared to TF (?12 mmHg). The results suggest that the higher number of hydrophobic amino acid residues LY and RALP contributed to their higher in vitro and in vivo activities when compared to TF.