Measurement of protein hydrolysis
Protein hydrolysis was measured using the method of pH-state (Adler-Nissen,
1986). Casein was mixed in distilled water with help to dissolve in 0.1M
NaOH. Temperature and pH were adjusted to the optimum values for each
proteinases. The casein was hydrolyzed by the five proteinases mentioned
above. During process of casein hydrolysis, hydrolysis pH was maintained at
the prescribed value by continuously adding 0.1M NaOH, and the
consumption of alkali liquor was recorded every 30min for 6h. The degree of
hydrolysis was quantified according to the following equation: