Isolation and structural analysis of antihypertensive peptides that exist naturally in Gouda cheese

Seven kinds of ripened cheeses (8-mo-aged and 24-mo-aged Gouda, Emmental, Blue, Camembert, Edam, and Havarti) were homogenized with distilled water, and water-soluble peptides were prepared by C-18 hydrophobic chromatography. The inhibitory activity to angiotensin I-converting enzyme and decrease in the systolic blood pressure in spontaneously hypertensive rats were measured before and after oral administration of each peptide sample. The strongest depressive effect in the systolic blood pressure (-24.7 mm Hg) and intensive inhibitory activity to angiotensin I-converting enzyme (75.7%) were detected in the peptides from 8-mo-aged Gouda cheese. Four peptides were isolated by HPLC with reverse-phase and gel nitration modes. Their chemical structures and origins, clarified by combination analyses of protein sequencing, amino acid composition, and mass spectrometry, were as follows: peptide A, Arg-Pro-Lys-His-Pro-Ile-Lys-His-Gln [α_s1-casein (CN), B-8P; f 1-9]; peptide B, Arg-Pro-Lys-His-Pro-Ile-Lys-His-Gln-Gly-Leu-Pro-Gln (α_s1CN, B-8P; f 1-13); peptide F, Tyr-Pro-Phe-Pro-Gly-Pro-Ile-Pro-Asn (β-CN, A²-5P; f 60-68); and peptide G, Met-Pro-Phe-Pro-Lys-Tyr-Pro-Val-Gln-Pro-Phe (β-CN, A²-5P; f 109-119). Peptides A and F, which were chemically synthesized, showed potent angiotensin I-converting enzyme inhibitory activity with little antihypertensive effects.