The nature of cyclic fatty acids formed in heated vegetable oils

The nature of the complex mixtures of monocyclic fatty acids formed in heated sunflower oils and linseed oil are summarized. The analytical approach involved fractionation of total cyclic fatty acids by silver ion high-performance liquid chromatography and characterization by gas chromatography - mass spectrometry of the picolinyl esters and/or dimethyloxazoline derivatives and Fourier transform infrared spectroscopy of the methyl esters. The cyclic fatty acids derived from oleate were saturated, those from linoleate were monoenes and those from linolenate were dienes. They contained five- and six-membered rings and differed according to the positions and configurations of the double bonds and rings. Possible mechanisms for their formation via allylic radical intermediates are discussed.