Detection of the changes in fatty acid composition and physicochemical properties in selected edible oils heated at different degrees of time

The study investigated the changes in chemical and fatty acid composition in selected edible oils due to continuous heating. Peroxide value of all the oil except rice bran oil went beyond the permissible limit of 10 mEqO2/kg after 90 min of heating. At first degree of heating, the saponification number of all the oils increased. But the values declined after second and third time of heating, indicating a high degree of saturation. Rice bran oil showed the most slower decreasing trend in case of iodine value. Acid value of all the oils increased with time of heating indicating the presence of free fatty acid. Fatty acid composition of all the oils seemed to be affected due to continuous heating when analyzed with GC–MS. Presence of essential fatty acids was affected and fully absent in some oil. Some foreign chemicals like glycidyl fatty acid esters, fumaric acid, succinic acid, cyclohexane, etc. were detected due to the heating of oils. Glycidyl fatty acid esters were discovered in the degradation of each oil. Cyclohexane is produced during the breakdown of palm and soybean oil. Conferring to the results, it is recommended that oils should not be used after the third degree of heating.