Alkaline Phosphatase
Cheese MoleculeAn enzyme found in milk used to measure the adequacy of pasteurization
Alkaline phosphatase is an enzyme naturally produced by cows. Some of this enzyme ends up in their milk. A special property of enzymes is their heat instability. Many enzymes will stop functioning when they are subjected to a certain temperature for a certain amount of time. This is due to their 3-D structure being changed, or “denatured” as it’s called.
The structure of alkaline phosphatase. This structure is from the enzyme derived from GM E coli. (1ALK)
Visualized using 3Dmol.js.
The thermal resistance of alkaline phosphatase is greater than that of some common pathogenic microorganisms found in milk (e.g. Mycobacterium tuberculosis). Therefore, fluid milk that shows a negative result when tested for alkaline phosphatase is considered properly pasteurized. Cheese can also be tested for residual alkaline phosphatase, but results can be spurious since some microbes produce phosphatases and can give false positive results.
The figure above shows the temperature/time relationships for common pathogens and enzymes in milk. Basically, the further right and up you go on the graph, the more kill. Alkaline phosphatase is the red line.
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