Use of a fluorimetric test for bovine alkaline phosphatase to demonstrate under-pasteurisation of skimmed milk and cream

Investigations were undertaken at two small farm dairies noted to have sporadic failures of statutory phosphatase tests on samples of cream. Bottled whole milk and skimmed milk from both dairies appeared to be satisfactory. Use of the highly sensitive fluorimetric phosphatase test enabled us to demonstrate that diversion of heat-treated whole milk to a separator resulted in under-pasteurisation. This was due to increased flow rate through the holding tube and was confirmed by a simple timing experiment. Modification of high-temperature-short-time pasteurisers in order to produce a range of products may affect the dynamics of flow resulting in inadequate heat-treatment and possibly in survival of microbial pathogens.