Monocyclic saturated fatty acids formed from oleic acid in heated sunflower oils

Fractions of saturated cyclic fatty acids, formed from oleic acid in normal and high-oleate sunflower oils during small-scale frying operations, were isolated by silver ion high-performance liquid chromatography. By means of gas chromatography of the methyl esters and gas chromatography/mass spectrometry of the dimethyloxazoline derivatives, eight monocyclic saturated fatty acids, comprising four basic structures, were identified: cyclopentyl fatty acids with rings from C-5 to C-9 and C-10 to C-14, and cyclohexyl fatty acids with rings from C-4 to C-9 and C-10 to C-15 of the original fatty acid chain. Each structure was represented by two components corresponding to cis and trans ring isomers. The cyclopentyl fatty acids were twice as abundant as those with a cyclohexane ring. Possible mechanisms for formation of the cyclic fatty acids via radical intermediates are discussed.