Effects of milk-flavoring constituents on the fluorometric assay of bovine alkaline phosphatase / by Elizabeth Brock.

"Determining the activity of residual alkaline phosphatase (ALP, EC 3.1.3.1) in milk validates adequate pasteurization and confirms that cross-contamination of raw milk has not occurred, thus ensuring product safety. However, flavored milks have been shown to yield false positive or false negative ALP activities, which inaccurately represent the microbiological safety of the milk sample. The objectives of this study were to determine the effects of 1) homogenization, 2) pasteurization conditions, and 3) ingredient inclusion on residual ALP activity using the fluorometric assay for analyses. Preliminary work determined no significant differences (P > 0.05) in ALP activity as a function of dual-stage homogenization (1,500 and 500 psi) or differing pasteurization methods including high temperature, short time (HTST, 72oC for 15 s) and low temperature, long time (LTLT, 63oC for 30 min). Pure vanilla extract, cocoa powder, or sucrose was added to standardized 3.25% fat raw milk at 0.1, 1.5, and 8%, respectively. A control (no ingredients) was included as the fourth group. All four treatments were pasteurized at HTST conditions. ALP activity did not significantly differ among treatment groups (P > 0.05) and was adequately inactivated (< 350 mU/L). However, the treatment containing cocoa powder had the highest ALP activity at 106.70 mU/L in comparison to the control at 19.32 mU/L, suggesting the primary polyphenols of the ingredient are inducing a conformational change of the enzyme or interacting with the quantified fluorescence produced. With flavored milk sales rising in recent years, ensuring product safety and understanding potential interactions are imperative in the dairy industry."--Page ii.

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