Determination of Bacterial ATP Levels in Raw Milk: Selectivity of Non-Bacterial ATP Hydrolysis

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Abstract
The selective destruction of non-bacterial ATP and subsequent determination of bacterial ATP using the ATP bioluminescent technique was investigated. Treatments to release ATP from somatic cells and hydrolyze free ATP also significantly reduced the ATP content of Enterobacter cloacae in skim and raw milk. The reduction can mainly be ascribed to apyrase (an ATPase) affecting the ATP content of intact bacteria. Somatic cell treatments failed to completely eliminate non-bacterial ATP. Although treatment with a somatic releasing reagent, EDTA and apyrase, resulted in a 96% reduction in the ATP content of raw milk, the remaining non-bacterial ATP was still considerably more than found in the bacterial component of raw milk studied here. Until reagents are available to selectively destroy all non-bacterial ATP without affecting the bacterial ATP content, the bioluminescent technique will have limited application in determination of the bacterial quality of raw milk.