Question

Lyophilization or freeze-drying involves

• A. Freezing the cells in liquid nitrogen
• B. Sublimation of cells water by its drying under vacuum
• C. Making into powder by dry heat
• D. Wet heat and freezing of cells

Hint:

• Lyophilization = Freeze-drying.
• Process: Freeze the material \(\rightarrow\) Reduce pressure (vacuum) \(\rightarrow\) Ice sublimes (solid \(\rightarrow\) gas).
• Used for preserving sensitive biological materials, pharmaceuticals, food.

Answer 1

The Correct Option is B

Lyophilization, also known as freeze-drying, is a dehydration process typically used to preserve perishable materials or make the material more convenient for transport. It works by freezing the material and then reducing the surrounding pressure to allow the frozen water in the material to sublimate directly from the solid phase to the gas phase. The key steps are:
1. Freezing: The material (e.g., a cell culture, food, pharmaceutical) is frozen, usually to a very low temperature.
2. Primary Drying (Sublimation): The frozen material is placed under a vacuum, and the pressure is reduced below the triple point of water. Heat may be gently applied to provide energy for sublimation. The ice in the material turns directly into water vapor without passing through the liquid phase. This vapor is then removed (e.g., by a condenser).
3. Secondary Drying (Desorption): After most of the ice has sublimated, some unfrozen water molecules may still be bound to the material. The temperature is slightly raised (while still under vacuum) to remove this residual moisture by desorption.
Let's analyze the options:
(a) "Freezing the cells in liquid nitrogen": Freezing is the first step, but lyophilization is more than just freezing.
(b) "Sublimation of cells water by its drying under vacuum": This correctly describes the core principle of lyophilization – removing water by sublimation under vacuum. "Cells water" implies water within the cells.
(c) "Making into powder by dry heat": Dry heat would typically denature or destroy biological materials. Lyophilization aims to preserve them.
(d) "Wet heat and freezing of cells": Wet heat (like autoclaving) sterilizes by killing cells. Freezing is part of lyophilization, but "wet heat" is contradictory to the preservation goal.
Therefore, option (b) best describes the process. \[ \boxed{\text{Sublimation of cells water by its drying under vacuum}} \]