Table 1 shows the main chemical characteristics of the seven samples used in the thermal oxidation assays, presented in increasing order of degree of unsaturation. The three basic oils enormously differed in their fatty acid composition. The linoleic acid content was very low for HOHPSO and HOSO (2.4% and 5.1%, respectively), in contrast to the high content in HLSO (56.8%). The preparation of the four binary mixtures was performed to give increasing concentrations of linoleic acid, which is the fatty acid most susceptible to degradation in sunflower oils. Thus, HOHPSO and HOHPSO/HLSO 95:5 differed essentially in the content of lino- leic acid, which was double for the latter, while HOHPSO/HLSO 95:5 and HOSO, which presented the same content of linoleic acid, only differed in the content of saturated and monounsaturated acids. The rest of the mixtures are characterised by similar con- tents of saturated acids, with varying contents of oleic and linoleic acids. All the samples had a-tocopherol as the major natural anti-
oxidant, but at variable contents, ranging from 283 to 747 mg /kg. The oil stability index (OSI) values were quite different according to the oil composition, ranging from 4.8 to 34.4 h at 110 °C. The HOHPSO showed a remarkably high OSI value, which makes it pos- sible to be used as a vegetable oil of potential applications in those processes using partially hydrogenated oils (Guinda, Dobarganes, Ruíz-Méndez, & Mancha, 2003). Free fatty acids (lower than 0.05%) and peroxide values (lower than 3 meq O2/kg) were similar for the three oils and the binary mixtures and typical of fresh re- fined oils of good quality.