Question

Given below are two statements, one is labelled as Assertion (A) and other one labelled as Reason (R).
Assertion (A): In freeze drying technique, water from frozen food is sublimed off.
Reason (R): Freezing is a preservation method in which food sealed in container is subjected to elevated temperature for definite period of time.

• A. Both (A) and (R) are true and (R) is the correct explation of (A).
• B. Both (A) and (R) are true but (R) is NOT the correct explation of (A).
• C. (A) is true but (R) is false.
• D. (A) is false but (R) is true.

Hint:

Sublimation is the phase change directly from solid (ice) to gas (vapor). Freezing preserves food by lowering temperature to reduce water activity and slow microbial growth, not by heating.

Answer 1

The Correct Option is C

Step 1: Understanding the Concept:
Evaluating the physical principles of food preservation methods like freezing and freeze drying is essential for proper process design.
Freeze drying (lyophilization) is a high-quality dehydration process, whereas freezing is a low-temperature storage preservation method.

Step 2: Detailed Explation:
Let us alyze both statements independently:
- Assertion (A): In freeze drying, the food is first frozen, and then placed under a vacuum.
Under low pressure, heat is applied to sublime ice crystals directly into water vapor, bypassing the liquid phase.
This sublimation process preserves the structural integrity, nutritiol value, and flavor profile of the food.
Thus, Assertion (A) is chemically and physically true.
- Reason (R): Freezing is a preservation method that operates by lowering the temperature of the food, typically below \(-18^\circ\text{C}\).
This low temperature slows chemical reactions and stops microbial growth by freezing free water into ice.
The description in Reason (R)—"subjected to elevated temperature for a definite period of time"—defines thermal sterilization or canning, not freezing.
Therefore, Reason (R) is completely false.

Step 3: Fil Answer:
The Assertion is true, but the Reason is false because freezing does not involve elevated temperatures.
Hence, the correct option is (C).