THE APPLICATION OF THE PHOSPHATASE AND TURBIDITY TESTS TO STERILISED MILK

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Abstract
SUMMARY: 1. The possiblity of obtaining high “ phosphatase” test results in the laboratory on overheated sterilised milk is demonstrated. This is not so pronounced with sterilised milk that has not been homogenised. A correlation is shown to exist between the “ phosphatase ” result and the temperature and duration of heating of sterilised milk. (In milk heated to temperatures of 100°C. or lower, an inverse correlation exists).2. Control (unicubated) phosphatase test are shown to give higher results than completed (incubated) phosphatase tests in overheated sterilised milk.3. The high “ phosphatase ” values are not caused by liberation of phenolic substances as results obtained with the use of either buffered substrate or buffered water are similar.4. It is suggested that an indication of overheating is provided by the excess of values of the control over the completed phosphatase test.5. When Aschaffenburg's turbidity test is applied to overheated sterilised milk the extent of overheating can be judged by the intensity of yellow colour in the nitrate. This modification to Aschaffenburg's test still requires extensive trials, but the measurement of efficiency of heating and extent of overheating in one test appears possible.6. To estimate overheating by the modification to Aschaffenburg's turbidity test it is necessary to use a Lovibond Tintometer as no discs for the colour values are available. Laboratories possessing only a Lovibond Comparator will be obliged to use the completed and control phosphatase tests in parallel: this requires 24 hours incubation whereas the modification to Aschaffenburg's test can be completed without incubation.7. Hitherto there has been no satisfactory laboratory control test to determine overheating of sterilised milk. It is suggested that the use of either of the above two methods could be used to prevent detrimental overheating of milk and also could result in fuel economy.