Determination of proteolytic activity in different milk systems

A method for the determination of proteolytic activity in whole milk, skim milk or in a solution similar to skim milk ultrafiltrate was optimized and validated. An artificial substrate (azocasein) was used to quantify the enzyme activity through the release of a chromogenic product that was measured spectrophotometrically after clarifying the samples by the addition of trichloracetic acid. The method gave linear results in the range of 0–50 mU/ml of added Bacillus subtilis protease and the least detection and quantification limits were 2.29 and 7.64 mU/ml of protease, respectively. The precision, measured as relative standard deviation, was between 1.14 and 7.99% and mean recovery ranged between 99 and 104%. Reliability of the method was satisfactory for all products evaluated.