Question

Heating of unsaturated fats and oils, as in frying operations, can produce changes in the color, molecular weight, viscosity or refractive index due to

• A. Rancidity
• B. Hydrogenation
• C. Polymerization
• D. Termination

Hint:

When frying oil gets old, it becomes thick, gummy, and dark. This is primarily due to polymerization, where small fat molecules link up to form large, heavy polymers.

Answer 1

The Correct Option is C

Step 1: Consider the conditions of deep frying. Frying involves heating oils to high temperatures (typically 160-190\(^\circ\)C) for extended periods in the presence of air and water (from the food).
Step 2: Analyze the chemical changes that occur under these conditions. Unsaturated fatty acids in the oil are susceptible to various reactions. While oxidation (leading to rancidity) does occur, a key reaction at high frying temperatures is polymerization. Here, fatty acid molecules join together to form larger molecules called polymers. This process directly leads to an increase in molecular weight, which in turn causes a significant increase in the oil's viscosity (it becomes thicker). These larger molecules also affect the color and refractive index. Hydrogenation requires a catalyst and is not a primary process in frying. Termination is a step in a chain reaction, not the overall process.