Oxidation at elevated temperatures: Competition between α-tocopherol and unsaturated triacylglycerols

The competitive oxidation between α-tocopherol and unsaturated fatty acyls at thermoxidation conditions (180 and 240°C) was evaluated using purified triacylglycerols from nine fats and oils (refined coconut, palm, tallow, olive, high oleic sunflower, sunflower, corn, soybean, and flaxseed oil). α-Tocopherol degraded faster in less unsaturated lipids and a linear correlation between the iodine value (x) and the residual tocopherol content (y) was obtained after 2 h of heating at 240°C (y = 3.72x + 137.5, R² = 0.9463). The formation of polar oxidation products was established and the results were explained by a non-selective oxidation of unsaturated fatty acyls and α-tocopherol by highly reactive alkoxyl and hydroxyl radicals generated by decomposition of hydroperoxides.