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A thermoxidation process has been applied to extra-virgin olive oil to develop new knowledge on the evolution of the volatile compounds responsible for virgin olive oil flavor during oxidative deterioration. The initial volatiles (a total of 60), many of them responsible for the pleasant sensory characteristics of the oil and produced mainly through biochemical pathways, disappeared in the first hours, and the formation of off-flavors, produced through oxidative pathways, gradually increased. The main volatile compounds possibly responsible for off-flavors (51) were identified, and their evolution during the oxidative process was studied. The fatty acids content was determined during the process. Unsaturated fatty acids were found to be the main precursors of the volatile compounds found in oxidized samples. The early measurement of nonanal (which was not detected at all, or only at trace levels, in extra-virgin olive oil samples) could be an appropriate method to detect the beginning of the oxidation. The ratio hexanal/nonanal was used to differentiate between oxidized and good-quality virgin olive oil samples. Sensory evaluation of the samples and peroxide value agreed on the evolution of the oxidation. Keywords: Oxidation; volatiles; flavor; off-flavor; virgin olive oil

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One hundred and thirty-eight edible oil and fat samples from 21 different sources, either vegetable (Brazil nut, coconut, corn, high oleic sunflower, olive oil, peanut, palm, palm kernel, rapeseed, soybean, sunflower, etc.) or animal (butter, hydrogenated fish, and tallow) have been analyzed. The spectral features of the most noteworthy bands are studied, and their correlations with the amount of fatty acids quantified by gas chromatography are presented. Principal component analysis is applied to classify the set of samples by their level of unsaturation [saturated (SFA), monounsaturated (MUFA), and polyunsaturated fatty acids (PUFA)]. The most remarkable MUFA and PUFA oil sources are independently classified by applying stepwise linear discriminant analysis to the Raman shifts selected by their correlation with fatty acids or structural assignments. The results show that FT-Raman spectra not only have information of the degree of unsaturation but also of the balance among the amounts of SFA, MUFA, and PUFA. The scattering intensities near different Raman shifts (3013, 1663, and 1264 cm-1) show high correlations with the fatty acid profile determined by gas chromatography. Keywords: Oils and fats; FT-Raman spectroscopy; chemometrics