The objective of this work was to study the evolution of oxidation in sunflower oils differing in unsaturation degree during long-term storage at room temperature. For this purpose, a combination of adsorption and size-exclusion chromatographies was used for quantification of oxidized triacylglycerol (TG) monomers, dimers, and polymers. Conventional sunflower oil, genetically modified high-oleic sunflower oil, and a 1:1 mixture of the two were used. Results showed that oxidized TG monomers were the only group of oxidation compounds increasing during the early oxidation stage, and an excellent correlation was found between amounts of oxidized TG monomers and PV during the induction period, independently of the degree of oil unsaturation. Both the rate of formation and the amount of oxidized TG monomers accumulated at the end of the induction period increased as the unsaturation degree of the oils tested was higher. The end of the induction period was marked by the initiation of polymerization and exhaustion of tocopherol. Therefore, the concomitant determination of oxidized TG monomers and polymerization compounds provided a complete picture of the oxidation process.

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Methods are described for the direct determination of Al, Cr, Cu, Fe, Ni and Pb by atomic absorption spectrophotometry in sunflower oil and olive oils. Metallic contamination after storage under different controlled conditions and in contact with carbon steel, austenitic steel, ferritic steel and aluminum was examined. Additionally, chemical characteristics related to quality (acid value, peroxide value, K270 and oxidative stability) and some physical parameters of interest were evaluated after storage. When the samples were atomized directly off the tube wall, matrix interferences were not observed in the determination of Cr, Cu, Ni and Pb, whereas such interferences were noted when Al and Fe were determined. The results indicated that the L'Vov platform for Al and Fe determinations eliminates the matrix effects. Contamination with Fe was only detected in the olive oil that had been in contact with carbon steel, Fe concentration increased from 120±12 to 3,520±157 ppb. The physicochemical characteristics were affected only by the storage conditions, regardless of the metal sheets with which they were in contact. Virgin olive oil showed lowered stability after storage in contact with a carbon‐steel sheet than when stored in absence of metal.

The objective of this work was to study the evolution of oxidation under oxidative stability index (OSI) conditions using the Rancimat apparatus. Sunflower oils with different degrees of unsaturation (conventional high-linoleic sunflower oil, genetically modified high-oleic sunflower oil, and a 1 : 1 mixture of both of them) and virgin olive oil were used. The sunflower oils were tested at 100 7C, while the olive oil was assayed at 100, 110 and 120 7C. Samples were analyzed at different time points and conductivity values, until the induction period (IP) was overpassed. A combination of adsorption and size-exclusion chromatography was used for the quantification of oxidized triacylglycerol (TG) monomers, dimers and polymers. Additionally, peroxide values (PV) and ultraviolet absorption at 270 nm (K 270 ), as well as losses of tocopherols, were measured. The results showed that oxidized TG monomers were the only group of oxidation compounds that increased during the early oxidation stage. The end of the IP was marked by the initiation of polymerization after the exhaustion of tocopherols. In comparison with reported results obtained at room temperature, the main difference found was that the amounts of oxidation compounds at the end of the IP were much lower at OSI test temperatures. With the exception of the K 270 values, the results also showed that the IP endpoints provided by the OSI test were slightly higher than those obtained by quantification of oxidized TG monomers or by PV determination.

The effects of temperature and addition of alpha-tocopherol were evaluated in trilinolein model systems through quantification of oxidized TAG monomers, dimers, and polymers following oxidation at different temperatures. Samples of trilinolein without and with 250 and 500 mg/kg alpha-tocopherol added were stored at 25, 60, and 100 degrees C. Quantification of oxidized monomers, dimers, and polymers by a combination of adsorption and exclusion chromatography provided a useful measurement for studying the evolution of oxidation. Results showed that the amounts of primary oxidation compounds (trilinolein oxidized monomers) that accumulated during the induction period decreased as the temperature increased, indicating that the slope of the initial linear stage of oxidation depended on temperature. The end of the induction period was marked by a sharp increase in the levels of total oxidation compounds, the initiation of polymerization, and the loss of alpha-tocopherol. Addition of alpha-tocopherol did not prevent, but rather delayed, formation of trilinolein oxidized monomers and the initiation of polymerization.

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