2.7. Angiotensin I‐converting enzyme (ACE)‐inhibitory activity assay

The ability of protein hydrolysates and peptide fractions to inhibit the activity of ACE was determined using FAPGG as the synthetic substrate (Lin, Alashi, Aluko, Sun Pan, & Chang, ²⁰¹⁷). The samples (1 mg/ml) and 0.5 m/m FAPGG were dissolved in 50 mM Tris‐HCl buffer containing 0.3 NaCl at pH 7.5. Then, 10 µl ACE (0.5 U/ml final activity of 25 mU) was added to 170 µl of FAPGG and 20 µl of sample. The rate of decrease in absorbance at 345 nm was monitored at regular intervals for 30 min at 37°C in a microplate reader (Multiskan Go; Thermo Fisher Scientific). Captopril (1 mg/ml) was used as a positive control, while Tris‐HCl buffer was used as the negative control. ACE activity is expressed as the rate of reaction (ΔA/min), and the inhibitory activity was calculated as follows:

where A/min(sample)/ΔA/min(control) are ACE activity in the presence and absence of the peptides, respectively.