In pasteurization when heat treated, become denatured and stop the enzymes from functioning. This helps to stop pathogen growth by stopping the functionality of the cell.

Introduction:
When milk is heated at 62°C for 30 minutes and then cooled, the process is called pasteurization. This method is commonly used to kill harmful bacteria and extend the shelf life of milk. The correct answer to this question is option 'B'.

Explanation:
Pasteurization:
Pasteurization is a heat treatment process that kills or inactivates harmful microorganisms in food, particularly bacteria, while still preserving the flavor and nutritional value of the product. It was named after Louis Pasteur, a French scientist who developed this process in the 19th century.

Process:
The process of pasteurization involves heating the milk to a specific temperature and holding it at that temperature for a set period of time. In the case of milk, it is typically heated to around 62°C (145°F) for 30 minutes. This temperature is sufficient to kill most pathogenic bacteria and reduce the overall microbial load in the milk.

Effects:
- Killing harmful bacteria: The primary purpose of pasteurization is to kill or reduce the number of pathogenic bacteria present in the milk. This helps to prevent the transmission of diseases such as tuberculosis, brucellosis, and salmonellosis, which can be spread through contaminated milk.
- Extended shelf life: By reducing the number of bacteria in milk, pasteurization also extends its shelf life. This allows milk to be stored for longer periods without spoiling or becoming unsafe to consume.
- Preservation of flavor and nutrients: Unlike sterilization, which involves heating milk to much higher temperatures, pasteurization is a milder process that preserves the flavor and nutritional value of the milk to a greater extent.
- Retaining beneficial bacteria: Pasteurization does not eliminate all bacteria in milk. It only targets harmful pathogens while leaving behind certain beneficial bacteria that can contribute to the fermentation process in products like yogurt and cheese.

Conclusion:
The process of heating milk at 62°C for 30 minutes and then cooling it is called pasteurization. This method is commonly used to kill harmful bacteria, extend the shelf life of milk, and preserve its flavor and nutritional value. Pasteurization is an important process in the dairy industry to ensure the safety and quality of milk products.