The phosphatase inactivation curve is used to determine if pasteurization is adequate; what indicates a good result?

• A. Higher ALP/blue color
• B. Constant ALP regardless of color
• C. Lower ALP/less yellow color
• D. Increased ALP with increased brightness

Answer: (C)

Alkaline phosphatase activity in milk is used as a marker of pasteurization effectiveness—if the heat treatment is adequate, this heat-stable enzyme is inactivated, so the test should show little to no color development. The best result is indicated by low ALP activity, which corresponds to a weaker color (lower ALP/less yellow color). That means the enzyme was inactivated by the pasteurization process. In contrast, a strong color or blue color indicates more residual ALP and a heat treatment that wasn’t sufficient; a constant ALP level or increased ALP with brighter color likewise signals inadequate pasteurization.