Pasteurisation is a critical heat treatment process in the dairy industry to ensure milk safety by destroying harmful pathogens. To verify that the process has been carried out correctly, a naturally occurring enzyme in milk is tested for its activity. This enzyme acts as an indicator.
Step 1: Understanding the Question:
The question asks to identify the specific enzyme whose presence or absence is used to confirm that milk has been properly pasteurised.
Step 2: Detailed Explanation:
An ideal indicator enzyme for pasteurisation must have a thermal resistance slightly greater than that of the most heat-resistant pathogens found in milk (like Coxiella burnetii). This ensures that if the enzyme is destroyed, the pathogens have also been destroyed. Let's examine the options:
(A) Amylase: An enzyme that breaks down starch, not typically used as a pasteurisation indicator.
(B) Lipase: An enzyme that breaks down fats. Its activity can cause rancidity, but it is not the primary indicator for pasteurisation effectiveness.
(C) Phosphatase (specifically, Alkaline Phosphatase - ALP): This enzyme is naturally present in raw milk and is destroyed at the temperature-time combinations used for pasteurisation (e.g., 72$^\circ$C for 15 seconds). Its heat resistance is slightly higher than that of common pathogens. Therefore, a negative test for ALP activity post-pasteurisation confirms that the treatment was successful.
(D) Protease: An enzyme that breaks down proteins. Some proteases are very heat-stable and would survive pasteurisation, making them unsuitable indicators.
The absence of alkaline phosphatase is the standard industry test for adequate pasteurisation.
Step 3: Final Answer:
Phosphatase is the enzyme used as an indicator for the effectiveness of milk pasteurisation.