The enzyme _______ is almost completely inactivated during pasteurization.

The enzyme that is almost completely inactivated during pasteurization is alkaline phosphatase. This enzyme is naturally present in milk and is generally used as a marker to assess the effectiveness of the pasteurization process. When milk is pasteurized, it is subjected to high temperatures that typically lead to the inactivation of heat-sensitive enzymes, including alkaline phosphatase, which helps ensure that any pathogenic microorganisms are killed and improves the shelf life of the milk.

Alkaline phosphatase is specifically chosen because its presence indicates that the milk was not adequately pasteurized, as it should be significantly reduced or eliminated in properly pasteurized milk. The inactivation of alkaline phosphatase during pasteurization is therefore a critical factor in verifying the process's success and ensuring safety in milk consumption. In contrast, other enzymes like lipase, protease, and lactase can remain active or partially active after pasteurization, which is why they are not considered reliable indicators of pasteurization efficacy.