Study of conjugated fatty acids present in olive oil after thermal stress

First example of real structure determination of FAMEs present at trace level in complex matrices Olive oil market is suffering from illegal soft sophistication treatments. Blend olive oils are sometimes mixtures containing "lampante" oils submitted to thermal deodoration processes. A big effort is being devoted in order to find reliable markers able to unmask such adulterations. Our lab has been conducting for some years research in this field by the use of advanced analytical techniques, mainly mass spectrometry. Olive oils produced by legal processes have been compared to refined oils in order to find possible differences in the fatty acids composition. The fatty acids portion of oil has been converted into methyl esters and analyzed by GC-MS, using a Varian 2000 instrument. EI-MS, isobuthane and acetonitrile CI-MS and CI-MS/MS based methods have been used in order to elucidate the structure of an apparently anomalous component present at trace levels. Preliminary GC-FID experiments showed the appearance of a anomalous peak located at higher retention times with respect to linoleic acid methyl ester. Its intensity seems to be related to the heating of olive oil samples, remaining, anyway, at trace levels. EI-MS and isobuthane CI-MS measurements allowed to determine the molecular weight, 294 Da, and the candidate structure that could be related to a C18:2 FAME. Its retention time, significatively higher with respect to linoleic acid methyl esther suggested the possibility of a conjugated isomer. In fact, further acetonitrile CI-MS and CI-MS-MS experiments lead to the complete structure elucidation of this component, resulting in the 9,11-18:2 isomer. A definitive confirmation of the structure have been obtained by comparison with authentic 9,11-C18:2 standars, allowing also the determination of the stereochemistry, so that the compound under investigation resulted to be methyl 9(E),11(E)-octadecadienoate. Studies are still in progress in order to set up the quantitative assays