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 IC50 values of 165.3 μM and 65.8 μM, respectively. Kinetic studies revealed that Ile-Phe (Km: 3.1 mM, Papp: 2.4 × 10−6 cm/s) exhibited greater affinity toward the transport compared with Ala-Phe (Km: 48.1 mM, Papp: 1.4 × 10−6 cm/s) and Phe-Ile (Km: 12.7 mM, Papp: 1.4 × 10−6 cm/s).