535. Reactivation of milk phosphatase following heat treatment. III

Abstract

1. Of a number of farm milks examined, two have been found to develop a positive phosphatase reaction following pasteurization at 161° F. in a small H.T.S.T. plant. This phosphatase was not of bacterial origin but was reactivated milk phosphatase.2. Considerable variation in reactivation following pasteurization at 161° F. was found to occur using individual churns of the above farm milk from any one milking. Individual cow samples also showed similar variation when tested by the capillary method. No explanation of this variation is offered.3. Commercial bulk raw milk from road or rail tanks did not develop a positive phosphatase reaction after pasteurization at 161° F. on this plant.4. Cold storage of pasteurized milk susceptible to reactivation results in less reactivation, and some evidence was obtained that cold storage of the corresponding raw milk also results in less reactivation. No such effect has been observed either using the capillary method or with samples of Uperized milk.5. Pasteurizing at 170 and 180° F. usually resulted in increased reactivation as compared with that obtained after pasteurization at 161° F. Shortening the holding time at these two higher temperatures sometimes led to a further increase in reactivation.6. It is shown that no clear relationship exists between the results obtained by plant pasteurization and the capillary method.7. It is suggested that many of the reported cases of pasteurized cream developing a positive phosphatase reaction on storage can be attributed to reactivation of the enzyme.8. Practical implications of reactivation in relation to pasteurized milk are discussed.