2.7. Determination of angiotensin I‐converting enzyme (ACE) inhibitory activity

The inhibition of ACE was determined as described by Udenigwe, Lin, Hou, and Aluko (²⁰⁰⁹), using N‐(3‐[2‐furyl] acryloyl)‐phenylalanylglycylglycine (FAPGG), as substrate. An aliquot (1 ml) of FAPGG (0.5 mM, dissolved in 50 mM Tris‐HCl buffer containing 0.3 mM NaCl, pH 7.5) was mixed with 20 μl of 1 U/ml ACE (final assay activity was 20 mU) and 200 μl of sample solution (prepared in the Tris‐HCl buffer). Cleavage of the Phe‐Gly peptide bond in FAPGG results in a decrease in absorbance at 345 nm, which was recorded every 10 s for 2 min at room temperature. For control (uninhibited) reaction, peptide sample was omitted from the reaction mixture.

ACE inhibition was calculated as follows: