Modification of casein hydrolysates by plastein reaction and ACE inhibitory activity of the modified products

Casein was hydrolyzed by Neutrase under the fixed conditions to prepare casein hydrolysates that had the degree of hydrolysis of 13.0 % and value of IC50 about 40.4 μg/mL.The obtained hydrolysates then were modified by plastein reaction catalyzed by Neutrase.The effects of the addition level of Neutrase,the concentration of casein hydrolysates,reaction time and temperature on the plastein reaction of casein hydrolysates were studied by single factor experiments,with the decreased amount of free amino groups of the hydrolysates as the evaluation index.The results indicated that the suitable reaction conditions were addition level of Neutrase of 3 ku/g proteins,substrate concentration of 60%,reaction time of 6 h and reaction temperature of 20 ℃.Five modified casein hydrolysates were prepared with the selected reaction conditions but different reaction times.The analysis results showed that the modified hydrolysates had an improved ACE-inhibitory activity because their values of IC50 ranged from 14.7 to 31.1μg/mL.Our results indicated that Neutrase-catalyzed plastein reaction could be applied to enhance the ACE-inhibitory activity of casein hydrolysates,and reaction extent of plastein reaction showed impact on the ACE-inhibitory activity of the modified product.