Sunflower seed oils with different levels of oleic acid were investigated under temperature of frying conditions to evaluate their thermal and oxidative stability. The behavior of the oils was analysed on their contents of polar compounds, minor glyceridic compounds, triglyceride composition, induction time at 100oC and <FONT FACE="Symbol">a</FONT> -tocopherol levels. The results indicated lower polar compounds contents in high oleic sunflower oil than in normal sunflower oil. The results also showed an increase on total polar compounds mainly related on high molecular weight compounds, polymers, dimers and oxidized triglycerides monomers as thermal and oxidative reaction products. In contrast, the contents of diglycerides and free fatty acids, indicatives of the hydrolytic alteration, remain constant, once there was no moisture in the medium. The quantitative loss of the triglyceride composition was dependent on their insaturation degree and it was higher in triglycerides that contain two or three molecules of linoleic acid. The normal sunflower oil showed, in all experiments, a higher tendency to the polymerization, a higher degree of total alteration and a higher loss on its major triglycerides that on high oleic sunflower oil. In general, the results showed an excellent behavior of the high oleic sunflower oil related to the thermoxidation, independently of the heating type and to the discontinuous frying. Such results demonstrated that its thermal and oxidative stability was related on its low content of polyunsaturated fatty acids and high contents of oleic acid and triolein.
sunflower oil; oleic acid; frying oil; thermoxidation; total polar compounds; triglycerides