Abstract:

ACE inhibitory peptides with IC50 value of 47.1 μg/mL were prepared by hydrolyzing casein with alkaline protease from Bacillus subtilis and further modified by plastein reaction under the catalysis of the same protease in the presence of proline. The optimal conditions for plastein reaction were determined using response surface methodology at the fixed concentration of 35% (m/m) peptides and the reaction time of 6 h as follows: reaction temperature 47.8 ℃, molar ratio of proline to total free amino groups in ACE inhibitory peptides derived from casein 0.54, and addition level of alkaline protease 9.5 kU/g proteins. Under these optimal reaction conditions, a maximal decrease of free amino groups in reaction mixture of 195.7 μmol/g proteins was obtained. Six modified products with different modification degrees were prepared by adjusting reaction time. ACE inhibitory activities and IC50 values of these modified peptides were also analyzed. Results indicated that ACE inhibitory activity of modified products revealed irregular change with increasing modification degree. When the reaction mixture had a decrease of free amino groups of 195.7 μmol/g proteins, there was a decline of IC50 value of modified products to 0.2 μg/mL.

Key words: casein, plastein reaction, ACE inhibitory peptide, alkaline protease, modification