The Phosphatase Test. A Review of the Literature on its Application for Detecting Irregularities in the Pasteurization of Milk and Dairy Products

Summary It has been shown that the enzyme phosphatase is present in all raw samples of milk, and that its thermal resistance is greater than that of any pathogenic organism which may be present in milk. Due to its inactivation at pasteurizing temperatures generally employed, it adapts itself ideally to detecting irregularities in the pasteurization of milk. The various laboratory tests are of approximately equal value, and will detect variations as follows: 1.0° F. in temperature 5.0 minutes in holding time 0.1 per cent added raw milk to properly pasteurized. The modified field test is almost as sensitive; and increasing the incubation time to 30 minutes will probably make it just as sensitive as any of the laboratory tests. It has the advantage of being able to be run directly in the plant in a very short time. Irregularities can be detected at once, shown to operator, and cause remedied. A photelometer may be used with the laboratory tests for greater accuracy in some cases. The test is very sensitive and precautions listed for each test must be followed closely. The test may be applied to cream, and homogenized milk without modification. For chocolate drinks and various ice creams it is necessary to run controls using buffered water in place of buffered substrate to detect the presence of any interfering substances. For cheese and butter special preparation of the samples are necessary. More work needs to be done with the test on these two products.