An approach to improve ACE-inhibitory activity of casein hydrolysates with plastein reaction catalyzed by Alcalase

The preparation method of casein hydrolysates with high ACE-inhibitory activity was studied by Alcalase-catalyzed hydrolysis coupled with plastein reaction. Casein hydrolysates with an IC₅₀ value of about 47 μg mL⁻¹ were first prepared by hydrolysis of casein with Alcalase and then modified with plastein reaction catalyzed by the same enzyme. The impacts of four reaction conditions on plastein reaction of casein hydrolysates were studied, and then optimal conditions were determined using response surface methodology with the decrease of free amino groups in the reaction mixture as response. When the concentration of casein hydrolysates was fixed at 35% by weight, the maximum decrease of free amino groups in the reaction mixture of 181.8 μmol g⁻¹ proteins was obtained. The optimum conditions for the above decrease were found to be an E/S ratio of 7.7 kU g⁻¹ proteins, reaction temperature of 42.7 °C and reaction time of 6 h. Analysis results showed that ACE-inhibitory activity of casein hydrolysates prepared could be improved significantly by plastein reaction. When casein hydrolysates were modified by plastein reaction, with a decrease of free amino groups in the mixture of about 154.7 μmol g⁻¹ proteins and 181.8 μmol g⁻¹ proteins, their IC₅₀ values could be decreased to 0.6 and 0.5 μg mL⁻¹.