Identification of ACE-inhibitory peptides in salt-free soy sauce that are transportable across caco-2 cell monolayers

In present study, we aimed to identify angiotensin I-converting enzyme (ACE)-inhibitory peptides from a salt-free soy sauce (SFS), a newly developed antihypertensive seasoning obtained by Aspergillus oryzae fermentation of soybean in the absence of salt, which can be transported through caco-2 cell monolayers. Through an Ussing transport investigation of SFS across caco-2 cell monolayers, three di-peptides, Ala-Phe, Phe-Ile and Ile-Phe, were successfully identified from the SFS as transportable inhibitory peptides. Ala-Phe and Ile-Phe, but not Phe-Ile, exhibited ACE-inhibitory activity with IC(50) values of 165.3 microM and 65.8 microM, respectively. Kinetic studies revealed that Ile-Phe (Km: 3.1 mM, P(app): 2.4 x 10(-6) cm/s) exhibited greater affinity toward the transport compared with Ala-Phe (K(m): 48.1 mM, P(app): 1.4 x 10(-6) cm/s) and Phe-Ile (K(m): 12.7 mM, P(app): 1.4 x 10(-6) cm/s).