Production, analysis and in vivo evaluation of novel angiotensin-I-converting enzyme inhibitory peptides from bovine casein

Novel angiotensin-I-converting enzyme inhibitory peptides were isolated from bovine casein hydrolysate prepared by AS1.398 neutral protease. The active hydrolysate obtained at 12 h hydrolysis showed the highest ACE-inhibitory activity and was further consecutively separated by ultrafiltration, and the 3 kDa permeate showed the highest ACE-inhibiting activity. This active fraction was further purified to yield two novel ACE-inhibiting peptides, whose amino acid sequences were Arg-Tyr-Pro-Ser-Tyr-Gly (κ-casein; f25–30) and Asp-Glu-Arg-Phe (κ-casein; f15–18), respectively. The IC50 value of the peptides were 54 ± 1.2 μg/mL and 21 ± 0.8 μg/mL, respectively. The Lineweaver–Burk plots revealed that the peptides acts as a non-competitive inhibitor. Antihypertensive effect in spontaneously hypertensive rats also revealed that single and repeated oral administrations of hydrolysates of bovine casein decreased systolic blood pressure significantly in spontaneously hypertensive rats (P < 0.01, P < 0.05). These results suggested that the peptide derived from peptides from bovine casein would be a beneficial ingredient for functional food or pharmaceuticals against hypertension.