Method for Predicting Minimum Detectable Residual Alkaline Phosphatase in High-Temperature, Short-Time Processed...

High-temperature, short-time (HTST) processed milk, cream and buttermilk were mixed with small portions (0 to 0.6%) of the raw milk product to obtain desired levels of residual alkaline phosphatase. Samples were subjected to the differential test to discern reactivation and analyzed for phosphatase activity by the rapid colorimetric test. The experimental data were fitted to a linear statistical model to determine the minimum detectable residual phosphatase (E_o) in the product. These observed values and the computed expected values were highly correlated, with a rank correlation coefficient of 0.956, which was significant at a = 0.05 level. The values of [E_o] varied depending upon the extent of phosphatase reactivation in the HTST product when the residual phosphatase was zero. As the differential values of reactivation (reactivated [E] of the control sample minus the reactivated [E] of diluted sample containing magnesium) increased, the [E_o] increased also. In general, the [E_o] in cream was greater than that in milk. A method is proposed for predicting [E_o] in liquid HTST products.