Antioxidative effectiveness of some natural antioxidants in sunflower oil

Sunflower oil has been oxidized at 25 and 100 degrees C in the presence and in the absence of 0.01, 0.02 and 0.05% 3,4-dihydroxybenzoic acid, caffeic acid, esculetin and fraxetin. 3,4-Dihydroxybenzoic acid shows no antioxidative activity at either temperature. Esculetin possesses a relatively low effectiveness at 100 degrees C (stabilization factor F = 1.3 for 0.05% esculetin), and at 25 degrees C it does not improve the oxidative stability. Sunflower oil is more easy to stabilize at 100 degrees C: F = 3.0 for 0.05% fraxetin, and F = 1.9 for 0.05% caffeic acid. Native sunflower oil is much more difficult to stabilize than are its kinetically pure triacylglycerols.