Effect of High-Temperature Short-Time Heat Treatments on Some Properties of Milk. I. Inactivation of the Phosphatase Enzyme

Summary Information was secured on the phosphatase activity of raw milk and the distribution of phosphatase in various milk fractions. The phosphatase is believed to be located to a large extent but not entirely at the fat-serum interface. Separation temperatures up to 120° F. did not appreciably change the distribution of the phosphatase in the cream and skim milk fractions. Separation of heated milks possessing various phosphatase activities showed that the lower the phosphatase activity in the milk the less the difference in the phosphatase activity in the cream over that in the milk. A standard of 1 p.p.m. phenol was selected as satisfactory destruction considering the limits of accuracy of the test and the smallest increase from a practical standpoint in phosphatase activity in cream over that in milk from which this cream was separated. A study was made of the kinetics of phosphatase inactivation by heat, and time-temperature relationships for the inactivation of phosphatase are given over the temperature range of 143 to 185° F. A mathematical solution for time-temperature cycles is given which takes into consideration accumulative effects of heating to the holding temperature in reducing the phosphatase activity to 1 p.p.m. phenol. Data secured with various rates of heating indicated that the mathematical solution is satisfactory for practical use in determining time and temperature necessary to give a negative phosphatase test in milk with various heating methods. It follows that, if the phosphatase test is used as the standard for adequate pasteurization, this mathematical solution can be applied to determine the proper time-temperature conditions.

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