Influence of heat on oxidative stability and on effectiveness of metal-inactivating agents in vegetable oils

Metal-inactivating agents, such as citric acid, sorbitol, lecithin, and carboxymethylmercapto succinic acid, are not active in unheated vegetable oils. Apparently trace metals present in normal glyceride oils are held within a complex of unknown structure. After heating an oil, the metals can be complexed by metal-inactivating agents, such as citric acid. The release of metals appears to be associated closely with the breakdown of the fatty acid hydroperoxides. Formation of some association or complex between the metal and the hydroperoxide group or between the metal and the unsaturated linkage of the fatty hydroperoxide is suggested. The metals are held very tenaciously within this unknown structure. Although the metal is not available as an uncomplexed metallic ion, it does behave as a very strong pro-oxidant catalyst. The application of heat releases the metal so it can be complexed by added metal inactivators.