Step 1: Understanding the Question:
We need an antioxidant that is fat-soluble, comes from a desert plant, and acts together with citric acid to slow down rancidity in fats.
Step 2: Key Concept:
Antioxidants used in fats can be natural (plant-derived) or synthetic. A synergist like citric acid does not stop oxidation by itself, it works by tying up trace metal ions that would otherwise speed up the reaction, and it boosts the effect of a true antioxidant used alongside it.
Step 3: Detailed Explanation:
Maleic acid is a simple synthetic acid, not a plant antioxidant. BHA is man-made, not plant-derived. Tocopherols come from vegetable oils, not desert plants. NDGA is extracted from Larrea divaricata, commonly called creosote bush or chaparral, a shrub that grows in the deserts of the southwestern United States and Mexico. It is fat-soluble and, because it also binds trace metals, its activity is boosted when citric acid is added alongside it.
Step 4: Final Answer:
The antioxidant is Nordihydroguaiaretic acid (NDGA), sourced from a desert shrub and synergized by citric acid.