In the alkaline phosphatase test, what color indicates pasteurization was adequate?

• A. No color change
• B. Less yellow
• C. More yellow
• D. Bright red

Answer: (B)

The test works by measuring residual alkaline phosphatase activity in milk or a similar product. Alkaline phosphatase converts a substrate to a yellow product when active. After proper pasteurization, the enzyme is largely inactivated, so the color developed is less intense. Therefore, a pale or less yellow color indicates that pasteurization was adequate because there is little remaining enzyme activity. If more yellow appears, it signals more enzyme activity and indicates insufficient heat treatment. The bright red color is not the expected outcome for this reaction, and while no color change can also indicate no enzyme activity, the typical interpretation in this context is that reduced yellow color signifies adequacy.