Step 1: Understanding the Problem:
The question asks which of the given oilseeds produces an oil that is most prone to oxidative rancidity due to its high concentration of polyunsaturated fatty acids (PUFA).
Step 2: Key Formula or Approach:
Lipid oxidation susceptibility depends directly on the number of double bonds present in the fatty acid chains.
Polyunsaturated fatty acids (PUFA), such as linoleic acid (18:2) and linolenic acid (18:3), undergo autoxidation much faster than monounsaturated fatty acids (MUFA) like oleic acid (18:1).
Step 3: Detailed Explanation:
• Sunflower Oil: Contains high levels of polyunsaturated fatty acids (typically 50% to 70% linoleic acid), making it highly susceptible to autoxidation in the presence of oxygen, heat, and light.
• Groundnut Oil: Primarily composed of oleic acid (MUFA, $\approx$ 40-50%) and relatively low to moderate amounts of PUFA, making it structurally more stable.
• Sesame Oil: Contains high levels of unsaturated fats but is naturally protected against rancidity by powerful endogenous antioxidants (e.g., sesamol, sesamolin).
• Rice Bran Oil: Features a highly balanced fatty acid profile (high MUFA, moderate PUFA) and is rich in natural antioxidants like gamma-oryzanol, which provide excellent thermal and oxidative stability.
Step 4: Final Answer:
Thus, sunflower oil has the highest risk of rancidity due to high PUFA content.