The phosphatase inactivation curve measures the activity of which enzyme in milk?

• A. Lipase
• B. Amylase
• C. ALP
• D. Protease

Answer: (C)

In milk pasteurization validation, you use the phosphatase inactivation curve to track alkaline phosphatase activity. Alkaline phosphatase is naturally present in milk and is relatively heat-stable compared with many other enzymes. By measuring how its activity declines with heat—often using a substrate like p-nitrophenyl phosphate—the curve shows how effectively the heat treatment inactivates this enzyme. If the enzyme is fully inactivated, it indicates the pasteurization conditions were reached and are likely sufficient to achieve the desired microbial kill. If alkaline phosphatase activity remains, the process may not have been adequate.

Other enzymes like lipase, amylase, or protease aren’t used as the standard indicator because their inactivation can vary more with milk source, composition, or conditions, making them less reliable as a universal process validation marker.