Microplate kinetic assay of ACE activity and response surface methodology of hydrolysis factors of peanut and cowpea flours by Alcalase

When the amino-terminus protected tripeptide N-[3-(2-furyl)acryloyl]-L-phenyl- alanylglycylglycine (FAPGG) was used as substrate to determine angiotensin I converting enzyme (ACE) activity/inhibition in vitro, different reference time intervals have been used to measure the absorbance change because of different reaction conditions and instruments. In this research, the kinetic reaction in which FAPGG is hydrolyzed by ACE to furylacryloylphenylalanine (FAP) and glycylglycine (GG) was closely examined through the use of an automatic microplate reader. The slopes of resulting kinetic curves for the first 15 min were used to calculate ACE inhibition. Peptide compositions of food protein hydrolysates determine the ACE inhibitory potency and depend on the specificity of the proteolytic enzyme and the hydrolysis conditions adopted for producing hydrolysates. For two important plant food protein hydrolysates, ACE inhibition began to plateau after peanut was hydrolyzed for 2.5 h by Alcalase and cowpea for 1 h. The effects of three hydrolysis factors, pH, temperature and enzyme to substrate (E/S) ratio, on ACE inhibitory activities of Alcalase hydrolysates of peanut and cowpea flours were investigated systematically using response surface methodology. The response surface models were established and the significance of each term in models was analyzed. Hydrolysis factors, temperature and E/S ratio showed significant effects, while pH had no significant effect over the range studied. Their optimal values were determined and were found to result in no great difference in ACE inhibition when compared to the hydrolysis conditions at the chosen central point.