CHARACTERIZATION OF ALDEHYDIC ACIDS IN USED AND UNUSED FRYING OILS

Aldehydic acids, expected to be present in auto-oxidised lipids as a r esult of decomposition of hydroperoxides by beta-scission reactions, w ere analysed in unused and ir. frying oils used fur two days. The oils studied were partially hydrogenated rapeseed/palm oil mixture, conven tional sunflower oil and high oleic acid sunflower oil. The method inv olved saponification of lipids, elimination of the unsaponifiable matt er, transmethylation and further fractionation of the methyl esters in to polar and non-polar fractions by silica column chromatography. Both fractions were analysed by high-performance size-exclusion chromatogr aphy to determine the levels of Iron-polar dimers, polar dimers and ox idised monomers. The polar fraction was also analysed by gas chromatog raphy and gas chromatography-mass spectrometry. Using this approach, t he aldehydic acid methyl esters: methyl 8-oxooctanoate, methyl 9-oxono noate, methyl 10-oxo-8-decenoate, methyl 11-oxo-9-undecenoate and meth yl 12-oxo-9-dodecenoate were characterised in used as well as unused f rying oils. (C) 1997 Elsevier Science B.V.