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-Recently, thermoanalytic methods have frequently been used in the characterization of oils and fats. In this work, thermoanalytic and kinetic parameters of sunflower oils, with and without antioxidants, were evaluated using thermogravimetry / derivative thermogravimetry and differential scanning calorimetry. The thermogravimetric profiles for the sunflower oils had similar characteristics, showing a level stretch indicative of stability up to about 200 o C. Thermal decomposition of these oils occurred in three stages, related to the decomposition of polyunsaturated, monounsaturated and saturated fatty acids, respectively. DSC curves show two events that characterize the polymerization and decomposition of triglycerides. The heat capacities of the sunflower oils, obtained by DSC, showed a good correlation and were dependent on the composition of fatty acids. The kinetic parameters, obtained by non isothermal thermogravimetry by the Coats and Redfern, Madhusudanan, Horowitz and Metzger and Van Krevelen methods, were dependent on the antioxidant used. Increasing the frying time produced a decrease in the onset of thermal decomposition temperature in the sunflower oils analyzed.

Viscosity, the measurement of the internal flow resistance of a liquid, constitutes an intrinsic property of vegetable oils. It is of remarkable influence in the mechanism of atomization of the fuel spray, in other words, in the operation of the injection system. This property is also reflected in the combustion process, whose efficiency depends the maximum power developed by the engine. This work aims at assessing the rheological behavior of castor oil, castor oil biodiesel, and undegraded and degraded biodiesel at different exposure times and temperatures. Castor oil biodiesel presents viscosity higher than diesel oil, but this drawback can be corrected by means of blends of both components at different proportions. The viscosity data indicated that the heat treatment leads to a degradation of the samples accompanied by an increase of the viscosity, probably because of interactions with intermediary compounds. The degraded samples presented a pseudoplastic behavior, once the flow index, m, is smaller than 1.

Biodiesel is defined as the monoalkyl ester derivative of long-chain fatty acids, originated from renewable sources, such as vegetable oils or animal fats. The most common use of biodiesel is direct substitution of fossil fuels in compression−ignition engines. The heating of vegetable oils can cause complementary decomposition reactions, in which the results can also lead to the formation of polymeric compounds. This work has been carried out to study the degradation process of biodiesel in different temperatures and exposure times. The degradation process of biodiesel affected its thermogravimetric and calorimetric profiles, indicating the formation of intermediary compounds. The spectroscopic data of degraded biodiesel suggested oxidative polymerization, confirming thermal data. In the degraded biodiesel at 210 °C for 48 h, the formation of gum occurred, indicating that oxidative polymerization was completed.

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-This article carried out the extraction of sesame oil by using three extraction techniques: supercritical fluid extraction (SFE), Soxhlet and sequential extraction. The SFE was performed using supercritical carbon dioxide (SC-CO 2 ) as solvent and ethanol as cosolvent. Tests were performed at 20 MPa, 35°C and a flow rate of 2.5 g CO 2 /min with a total extraction time of 210 minutes. The Soxhlet extraction was performed for 8 hours, using petroleum ether and ethanol as solvents, until the exhaustion of the oil contained in the seeds. The sequential extraction used ethyl ether, ethanol and water as solvents. The Soxhlet extraction was the most effective (58.93%), while the SFE technique obtained 26.47% as the best result. The antioxidant activity (AA) was determined by the β-carotene/linoleic acid system, with good oxidation inhibition percentages (29.32-83.49%) for all the extracts. The main fatty acids (FA) in sesame oil were oleic and linoleic acids.

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