Study On The Oxidative Stability Of Sunflower Oil

The sunflower oil is regarded as the high quality oil in the international market. But it is very prone to oxidation and rancidity in long-term storage, which would affect on the shelf life of their products. There are differences in different varieties of sunflower oil, and the main reason is their different contents of fatty acid and a-tocopherol.The oxidation of oil is affected by fatty acid and natural antioxidant. Therefore, in order to improve the oxidative stability of sunflower oil, the different sunflower varieties was evaluated to select sunflower varieties with stronger stability. And the effects of fatty acid and a-tocopherol on stability of sunflower oil were studied to determine the main factor of oil oxidation. Finally, different natural compounds were compared to select the compound with higher antioxidant activity, which can be used to improve the quality of sunflower oil efficiently. The main results were showed as follow:Four kinds of sunflower oil were chosen as research objects, which were heated by Schaal oven method for 12 consecutive days. Peroxide value, acid value, iodine vale, contents of conjugated dienes and conjugated trienes of sunflower oils were respectively determined, and the content of linoleate acid and a-tocopherol were analyzed by high performance liquid chromatography. The results showed that the peroxide value, acid value and iodine value within 6 d of Youkui No.6 did not exceed the national standard of sunflower oil. Besides, the content of linoleic acid and a-tocopherol of Youkui No.6 were the highest. It indicated that the oxidative stability of Youkui No.6 sunflower oil was better.The fatty acid content was determined by GC-MS, and a-tocopherol content was analyzed by HPLC. The results showed that the variation of unsaturated fatty acid in oxidizing process was significantly lower that of a-tocopherol. It indicated that the oxidative stability was affected more by the content of a-tocopherol than that of unsaturated fatty acid during the process of oxidation.The antioxidant activities of three kinds of natural antioxidants were study by using ABTS and DPPH, and the effect of different antioxidants on the oxidation of sunflower oil were evaluated by Schaal oven method. The results showed that the invitro antioxidant capacity of three kinds of antioxidants was in descending order: gallic acid> quercetin> α-tocopherol, and the antioxidant capacity of three kinds of antioxidants in sunflower oil was similar with descending order. It indicated that the gallic acid was both better in the antioxidant activity.