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What Is Alkaline Phosphatase?Alkaline phosphatase enzyme has thermal resistance greater than that of pathogen organisms commonly found in milk.The enzyme cleaves a phosphate group from the substrate, disodium phenyl phosphate, liberating phenol which then reacts with a colorproducing compound to give a blue color.The sensitivity allows for the detection of approximately 0.1 % raw milk contamination in pasteurized milk or the equivalent (i.e. under-pasteurization).Complete pasteurization will inactivate the enzyme to below levels which are detectable by conventional methods.Alkaline Phosphatase (ALP) is an enzyme naturally present in all raw milk, which is used as an indicator of proper milk pasteurization.How Has Phosphatase Activity Been Determined???

What Is Alkaline Phosphatase?
Alkaline Phosphatase (ALP) is an enzyme naturally present in all raw milk, which is
used as an indicator of proper milk pasteurization. Complete pasteurization will
inactivate the enzyme to below levels which are detectable by conventional methods.
Because the heat stability of ALP is greater than that of pathogens that may be present
in milk, the enzyme serves as an indicator of product safety. However, the failure to
detect ALP activity does not guarantee that the product is pathogen-free.
 How Has Phosphatase Activity Been Determined?
The classic test for the determination of alkaline phosphatase activity is the Scharer
Rapid Phosphatase Test. The enzyme cleaves a phosphate group from the substrate,
disodium phenyl phosphate, liberating phenol which then reacts with a colorproducing compound to give a blue color. The more enzyme activity present the more
phenol is liberated giving a deeper color blue. The intensity of the blue is then read
visually or with a spectrophotometer. The results of this procedure are expressed as
micrograms of phenol per mL of milk. A value of greater than 1 microgram is
indicative of improper pasteurization. The sensitivity allows for the detection of
approximately 0.1 % raw milk contamination in pasteurized milk or the equivalent
(i.e. under-pasteurization).
 Alkaline phosphatase enzyme has thermal resistance greater than that of pathogen
organisms commonly found in milk.