Abstract

Using pH-state method, when degree of casein hydrolysis was set as criterion, the optimal enzymatic reaction conditions were obtained as follows: pH 7.5 and temperature 55 ?. Based on the proteolysis catalyzed by trypsinase, the relationship between protein content (x) and initial velocity of enzymatic reaction (y) was discussed and the equation of y=0.1177x (R²=0.9927)was found as standard curve for the calculation of protein content. In addition, the protein contents in five kinds of commercial fresh milk were determined by enzyme hydrolysis method and GB method (biuret method). Protein content calculated by enzyme hydrolysis method could be confirmed by GB method and the analysis of t-test indicated that there was no notable difference between two methods. Furthermore, the determinate time of the rapid method was only 8 minutes (including samples’ preparation) and was 1/20 times than that of biuret method.

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