Fluorometric detection of active alkaline phosphatase and gamma-glutamyl transferase in fluid dairy products from multiple species.

Over the past 80 years, a variety of methods have been developed to detect underpasteurized or improperly pasteurized milks used in dairy products. Existing methods are hampered by duration of analysis, poor reproducibility, and in some cases the use of hazardous chemicals. To overcome these issues, two new methods have been developed using fluorogenic substrates for two marker enzymes, alkaline phosphatase and gamma-glutamyl transferase. In 30 min, up to 18 samples can be analyzed in triplicate by both methods on two separate 96-well plates. Sample preparation is not necessary for liquid milks when using these methods. The relative standard deviation for each assay is less than 9%, and the correlation coefficient for results of the two methods is greater than 0.98. Using the new methods, milks from four species and nine commercially available liquid milk products were tested. The new methods were also tested directly against an existing phosphatase method (Fluorophos) in spiked whole milk samples.