Question

Which of the following are examples of heat preservation of foods?
A. Blanching
B. Pasteurization
C. Concetration
D. Serilization
E. Dehydration
Choose the correct answer from the options given below:

• A. A, B and D only
• B. A, D and E only
• C. B, C and E only
• D. B, C and D only

Hint:

While dehydration often uses heat to evaporate moisture, it is classified as a moisture-removal preservation method.
Blanching, pasteurization, and sterilization are classified as thermal preservation methods because heat application is their primary preserving mechanism.

Answer 1

The Correct Option is A

Step 1: Understanding the Concept:
Food preservation techniques aim to inhibit microbial growth and enzymatic activity to extend shelf life.
These methods can be classified by their primary preserving mechanism, such as thermal (heat) treatment, moisture removal, or chemical addition.

Step 2: Detailed Explanation:
Let us analyze the primary preserving mechanism of each listed method:
- Blanching (A): A mild thermal treatment applied to fruits and vegetables prior to freezing or canning.
It involves exposing the food to boiling water or steam for a short period to denature and inactivate enzymes (such as polyphenol oxidase), preventing enzymatic browning and off-flavors.
- Pasteurization (B): A controlled thermal process that uses moderate heat (usually below \(100^\circ\text{C}\)) to destroy pathogenic vegetative microorganisms and extend shelf life (commonly used for milk and fruit juices).
- Sterilization (D - misspelled as 'Serilization'): A rigorous thermal process (typically using pressurized steam at temperatures above \(121^\circ\text{C}\)) that destroys all vegetative cells and highly resistant bacterial endospores, ensuring commercial sterility (commonly used in canning).
Therefore, Blanching, Pasteurization, and Sterilization are direct thermal (heat) preservation methods.
Conversely, Concentration (C) and Dehydration (E) primarily preserve food by physically removing water to reduce water activity (\(\text{a}_w\)), rather than relying on direct heat denaturation of microbes as their primary preserving mechanism.

Step 3: Final Answer:
The direct heat preservation methods from the list are Blanching, Pasteurization, and Sterilization (A, B and D only).