Question

________ is not a low pressures process.

• A. Freeze drying
• B. Flash evaporation
• C. Supercritical fluid extraction
• D. Hypobaric storage

Hint:

"Supercritical" states require high pressures and temperatures to cross the critical point. Supercritical $\text{CO}_2$ extraction routinely operates at pressures exceeding $100\text{ to }300\text{ bar}$ ($10\text{ to }30\text{ MPa}$), making it a high-pressure system.

Answer 1

The Correct Option is C

Step 1: Understanding the Concept:
Food preservation and extraction techniques utilize different physical conditions, including temperature, pressure, and solvent states, to achieve specific outcomes.
Detailed Explanation:
Let us evaluate the operating pressures of each listed process:
- Freeze drying (A): Operates under high vacuum (low pressure, typically below $611\text{ Pa}$) to allow ice to sublime directly into water vapor.
- Flash evaporation (B): Involves spraying a pressurized, heated liquid into a vessel kept at a lower pressure, causing rapid vaporization of volatile components. This is a low-pressure process.
- Hypobaric storage (D): Storage of fresh foods under reduced atmospheric pressure (vacuum) and controlled temperatures to slow respiration and extend shelf life.
- Supercritical fluid extraction (C): This is a high-pressure extraction technique.
It operates at pressures above the critical pressure of the solvent (for $\text{CO}_2$, this is above $7.39\text{ MPa}$ or $73\text{ atm}$) to maintain the solvent in a supercritical state, where it has the density of a liquid and the transport properties of a gas.

Step 2: Final Answer:
Supercritical fluid extraction is a high-pressure process, not a low-pressure process.