Antihypertensive effect of peptide-enriched soy sauce-like seasoning and identification of its angiotensin I-converting enzyme inhibitory substances.

We have developed a peptide-enriched soy sauce-like seasoning termed Fermented Soybean Seasoning (FSS), by modifying the process of soy sauce brewing. The FSS has a 2.7-fold higher concentration of total peptides than regular soy sauce. The angiotensin I-converting enzyme (ACE) inhibitory activity of FSS (IC(50) = 454 microg/mL) was greater than that of regular soy sauce (IC(50) = 1620 microg/mL). The FSS demonstrated antihypertensive effects both in spontaneously hypertensive rats and in Dahl salt-sensitive rats during continuous feeding. The ACE inhibitory substances were purified from FSS by reversed-phase chromatography. Ala-Trp IC(50) = 10 microM; Gly-Trp IC(50) = 30 microM; Ala-Tyr IC(50) = 48 microM; Ser-Tyr, IC(50) = (67 microM; Gly-Tyr, IC(50) = 97 microM; Ala-Phe, IC(50) = 190 microM; Val-Pro, IC(50) = (480 microM; Ala-Ile, IC(50) = 690 microM; Val-Gly, IC(50) = 1100 microM; and a nicotianamine, IC(50) = 0.26 microM. [corrected] The concentrations of these substances in the FSS were revealed to be higher than that of regular soy sauce through quantitative LC-MS/MS analysis.