It inhibits bacterial growth through dehydration
Explanation
The preservation of perishable food items, such as meat and fish, using common salt relies on the biological principle of osmosis and the reduction of water activity.
Detailed Analysis:
- Mechanism of Action: When common salt (Sodium Chloride) is applied to meat or fish, it increases the solute concentration outside the microbial cells present on the food surface. This creates a hypertonic environment.
- Process of Dehydration: Due to the concentration difference, water moves out of the bacterial or fungal cells through their semi-permeable membranes into the external environment. This process is known as exosmosis.
- Result: The loss of intracellular water leads to the shrinkage of the protoplasm away from the cell wall, a phenomenon called plasmolysis. Since water is essential for enzymatic activity and metabolism, the dehydrated microbial cells are unable to grow, reproduce, or survive.
- Incorrect Options:
- It kills bacteria by thermal generation is incorrect because salting does not generate significant thermal energy to kill bacteria.
- It converts protein into a resistant compound is incorrect because while salt can precipitate proteins ("salting out"), the primary preservation mechanism is not the conversion of proteins into resistant compounds.
- It hydrates the tissue to prevent decay is incorrect because salt removes water (dehydrates) rather than adding it.
Key Takeaway:
Common salt preserves food by creating a hypertonic environment that induces plasmolysis (dehydration) in microbial cells, thereby inhibiting their metabolic functions and growth.