Changes of antioxidant potential of cold-pressed edible oils from sunflower and sesame during storage

Cold pressed edible oil consumption has risen worldwide due to its health benefits over the refined oils. However, these oils have a tendency to be oxidized by temperature, light and oxygen resulting in unpleasantness and formation of toxic materials. The main object of our study was the changes of antioxidant activity of sunflower and sesame oil after 2 months storage in dark glass bottles. The antioxidant activity was determined by measuring the inhibition of conjugated diene hydroperoxides arising from linolenic acid oxidation. For the DPPH assay, the antioxidant activities of the oils were expressed as percentage of decolorization of a solution of the stable radical DPPH (2,2-diphenyl-1-picrylhydrazyl radical) at 517nm. The Trolox equivalent antioxidant assay (TEAC) employed in this study gives a measure of the antioxidant activity of methanol extracts against ABTS (2,20-azino-bis(3-ethylbenzothiazo line-6-sulphonic acid radical. The oxidation of sunflower oil was the most evident by application of DPPH radical assay. The antioxidant potential of sunflower oil was decreased by more than four times while antioxidant potential of sesame seed oil was almost half which can be lined to decreased activity of vitamin-E-active compounds. Hb assay in human blood indicated higher instability of sesame seed oil and the same tendency was noticed for TEAC assay. From the results presented in this work we can conclude that DPPH assay is strongly dependent on the amounts of tocopherols, while TEAC assay is more dependent to polyphenols and lignans which are dominant in cold- pressed sesame seed oil.