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7 pages, 3 figures, 7 tables.[EN] Monoepoxy compounds formed after heating methyl oléate\udand linoleate, triolein and trilinolein at 180°C for 5, 10 and 15\udhours, were characterized and quantitated after derivatization to\udfatty acid methyl esters by using two base-catalyzed procedures.\udStructures were identified by GC-MS before and after hydrogénation.\udA complete recovery of the epoxy compounds was obtained by\udcomparing results from methyl oléate and linoleate before and\udafter transesterification, and good repeatability was also attained.\udSimilar amounts of epoxides were found for methyl esters and\udtriglycerides of the same degree of unsaturation, although formation\udwas considerably greater for the less unsaturated substrates,\udmethyl oléate and triolein, possibly due to the absence of remaining\uddouble bonds in the molecule which would involve a lower\udtendency to participate in further reactions. On other hand,\udindependently of the degree of unsaturation of the model\udsystems and of the period of heating, significantly higher amounts\udof trar)s isomers were formed. Finally from comparison between\udthe amounts of epoxides and the level of polar fatty acids in\udsamples, it was deduced that monoepoxy compounds were one\udof the major groups formed under the conditions used.[ES] En este estudio se identifican y cuantifican los oempuestos epoxidados\udformados a partir de sistemas modelo de oleato y linoleato de\udmetilo, trioleina y trilinoleina, calentados a 180°C durante 5,10 y 15 horas.\udLa identificación se lleva a cabo mediante CG-EM en las muestras\udde esteres metílicos antes y después de someter a hidrogenación y\udpara su cuantificación se utilizan dos procedimientos de transesterificación\uden medio alcalino. La comparación de las cantidades obtenidas,\udantes y después de la derivatización de los sistemas modelo de\udesteres metílicos, permitió deducir que la recuperación fue completa,\udobteniéndose también una excelente repetibilidad. Las cantidades de\udepoxides encontradas fueron del mismo orden para esteres metílicos\udy triglicéridos del mismo grado de insaturación, aunque la formación\udfue considerablemente mayor en los sistemas menos insaturados —\udoleato de metilo y trioleina— posiblemente debido a la ausencia de dobles\udenlaces en la molécula, que limitaría su participación en\udposteriores reacciones. Por otra parte, independientemente del grado\udde insaturación del sustrato y del periodo de calentamiento, se encontraron\udcantidades significativamente más elevadas de los isómeros\udtrans. Finalmente, es posible deducir, por comparación con la\udcantidad total de compuestos de degradación, que los epoxides\udconstituyen compuestos mayoritarios en las condiciones utilizadas.O. Bordeaux was supported by a grant from EC\ud(Contract FAIR-CT97-5016). This work was funded\udin part by CICYT (Project ALI 98-0884).Peer reviewe

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Characterization, quantitation and evolution of monoepoxy compounds formed in model systems of fatty acid methyl esters and monoacid triglycerides heated at high temperature