AbstractsChemistry

It has long been known that fats and oils develop rancidity when exposed to the air. Atmospheric oxygen attacks the unsaturated triglyceride molecules with the formation of many oxidation products, among which peroxidic and carbonyl compounds are the most important. This deterioration of the fat results in the production of off-flavours and odours which render the fat unpalatable. Many chemical tests have been employed for the detection of rancidity which depend on the presence of these compounds. Recently a very sensitive method has been developed based on the oxidation of ferrous iron to ferric by the peroxides present in an oxidized fat. The ferric ion produced is determined colorimetrically as ferric thiocyanate. This method has recently been severely criticized by Lea, who stated that the method was subject to serious error owing to the interference of atmospheric oxygen. The presence of air in the reaction mixture has also resulted in high peroxide values of fats and oils when determined by other modifications of the ferrous salt method. It was the purpose of this study to investigate the ferric thiocyanate method, with a view to preventing this oxygen interference, and to compare the results given by several ferrous salt methods with those obtained by iodimetric procedures.