The Reactivation of Phosphatase in H.T.S.T. Pasteurized Dairy Products

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Abstract
Positive phosphatase tests, found in commercially short-time pasteurized 20% cream were due to reactivation of the enzyme following heat treatment, and prompted a study of conditions causing this reactivation in skim milk, whole milk, and cream. These products were short-time pasteurized for 16 seconds at 165[degree] to 240[degree]F, and also long-time pasteurized for 145[degree]-150[degree]F for 30 minutes. Immediately after pasteurization, all samples showed negative phosphatase, and remained so if the products were stored at 40[degree]F. When the products were held at 88[degree]F following heat treatment, however, reactivation of the phosphatase occurred in short-time pasteurized products, but not in similar products pasteurized by the long hold method. It also appeared that the higher the high temperature short time (H.T.S.T.) heat treatment, the greater the reactivation. In addition, the reactivation of the enzyme was associated with the fat content of the product; the higher the fat content, the lower the pasteurizing temperature, and the shorter storage time required to produce the reactivation. Bacteriological data indicated that the reactivated phosphatase was not of bacterial origin.