Residual alkaline phosphatase activity in pasteurized milk heated at various temperatures : Measurement with the Fluorophos and Scharer rapid phosphatase tests

Milk containing three levels of milkfat (skim [0.5%], lowfat [2.0%], and whole [3.25%]) were heat treated at five different temperatures (59, 61, 63, 65, and 67 degrees C) using a laboratory scale, batch pasteurization method. Heated milk samples were removed at 5-min intervals, immediately cooled, and then assayed using the quantitative fluorometric method and the qualitative Scharer rapid test. Mean alkaline phosphatase (ALP) activity values as measured with the Fluorophos method decreased in all milk preparations as the time of sampling and temperature of heating increased. Samples representing the three fat levels and heat treated at 63 degrees C for 30 min, the minimum time/temperature allowed by the 1995 pasteurized milk ordinance (PMO), had ALP activity values