Question:
Phosphatase test is negative in
Phosphatase test is negative in
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A "positive" phosphatase test in milk labeled as pasteurized indicates either under-pasteurization or contamination with raw milk.
Updated On: Jul 23, 2026
- Pasteurised milk
- Chilled milk
- Thermised milk
- Irradiated milk
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The Correct Option is A
Solution and Explanation
Step 1: Understanding the Concept:
The alkaline phosphatase (ALP) test is a fundamental biochemical test used in the dairy industry to verify the efficiency of the pasteurization process. Alkaline phosphatase is an enzyme naturally present in all raw milk.
Step 2: Detailed Explanation:
Alkaline phosphatase has a heat resistance slightly higher than that of the most heat-resistant non-spore-forming pathogen commonly found in milk, Coxiella burnetii. Therefore, if the heat treatment is sufficient to destroy ALP, it is assumed that all common pathogens have also been destroyed.
In pasteurized milk ($63^{\circ}$C for 30 min or $72^{\circ}$C for 15 sec), the ALP enzyme is denatured and inactivated. A "negative" result in the phosphatase test (no color change when substrate is added) indicates that pasteurization was successful. Chilled milk and thermised milk (low-heat treatment) still contain active ALP. Irradiated milk might reduce microbial load but does not specifically target enzyme denaturation in the same way thermal pasteurization does. Thus, the test is specifically designed for pasteurized milk verification.
Step 3: Final Answer:
The phosphatase test is negative in pasteurised milk.
The alkaline phosphatase (ALP) test is a fundamental biochemical test used in the dairy industry to verify the efficiency of the pasteurization process. Alkaline phosphatase is an enzyme naturally present in all raw milk.
Step 2: Detailed Explanation:
Alkaline phosphatase has a heat resistance slightly higher than that of the most heat-resistant non-spore-forming pathogen commonly found in milk, Coxiella burnetii. Therefore, if the heat treatment is sufficient to destroy ALP, it is assumed that all common pathogens have also been destroyed.
In pasteurized milk ($63^{\circ}$C for 30 min or $72^{\circ}$C for 15 sec), the ALP enzyme is denatured and inactivated. A "negative" result in the phosphatase test (no color change when substrate is added) indicates that pasteurization was successful. Chilled milk and thermised milk (low-heat treatment) still contain active ALP. Irradiated milk might reduce microbial load but does not specifically target enzyme denaturation in the same way thermal pasteurization does. Thus, the test is specifically designed for pasteurized milk verification.
Step 3: Final Answer:
The phosphatase test is negative in pasteurised milk.
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