Changes of Sunflower Oil Polyenoic Fatty Acids under High Temperatures

Heat induced <I>cis-trans</I> isomerisation of sunflower oils depending on temperature, reaction time and original content of linoleic acid was investigated. The content of isomeric fatty acids was determined by gas chromatography and the content of polymers by gel permeation high-performance liquid chromatography. The content of <I>trans</I> fatty acids increased with time and with temperature and a rate of <I>cis-trans</I> isomerisation and polymerisation depends on the temperature according to Arrhenius equation. The content of polymers was significantly lower in sunflower oil with high content of oleic acid because of the low concentration of linoleic acid in oil. In both oils the content of conjugated linoleic acid initially increased depending on time and temperature, however after certain time the stationary state occurred. Polymerisation of polyenoic fatty acids takes place directly with heat induced <I>cis-trans</I> isomerisation.