The Development of a Positive Phosphatase Test in Refrigerated, Pasteurized Cream

Commercially pasteurized cream which had been negative to the phosphatase test immediately after pasteurization developed a positive reaction after three days at 10 ° C.This change in reaction made possible erroneous conclusions as to the previous treatment of the cream, since the cream was still in a salable condition and the change had taken place well within the normal marketing time of the cream.Shippers of pasteurized cream claimed that their product was known to have left their plant with a negative phosphatase test, despite the fact that the cream tested positive on arrival at distant markets.These facts suggested the need for research on the development of a positive phosphatase test in refrigerated, pasteurized cream. LITERATUREThere are numerous review articles concerning the uses and limitations of the phosphatase test (3, 4, 5, 7, 15).Only a few workers have reported the development of a positive test after a negative test had been obtained on the product.Hammer and Olson (8) showed that a positive test developed in butter after storage.Brown and Elliker (2) claimed that flash pasteurized cream developed a positive test after the cream had been held at refrigeration temperatures.Wiley, Newman and Whitehead (16) stated that cream, flash pasteurized by the Vacreator method, and used for making butter, at first gave a negative phosphatase test but several hours after the addition of salt or sugar or the drying of the cream gave a positive reaction.They explained the change by theorizing that there was a binding of small and varying amounts of the enzyme in the cream in such a manner that the enzyme escaped destruction during very short heat treatments.Later this bound phosphatase was released and gave a positive reaction.The effect of bacteria on the phosphatase test has been studied by several workers.Paley ( 13) and Burgwald and Giberson (5) reported bacteria which gave positive reactions to the phosphatase test.Hammer and Olson (8) claimed that a number of species of Pseudomonas, species of Aerobacter, Flavobacterium fecale, some species of Alcaligenes, and Oospora lactis gave very strong phosphatase reactions.Leahy, Sandholzer and Woodside (11)found that species of Staphylococcus, Aerobacter and Klebsiella gave a true phosphatase test.However, they believed that unless large numbers of these