The effect of light on the oxidation of fats

Abstract

It has long been known that exposure to light exerts a powerful influence upon the deterioration of fats, and it has been claimed that light alone, in the absence of air, is capable of producing rancidity (Wagner, Walker and Oestermann, 1913). It is now, however, generally admitted that the action of light consists essentially in accelerating oxidation of the fat. To follow the changes induced in fats by exposure to air and light it is necessary (1) to have a quantitative knowledge of the state of oxidation in any specimens of fat; (2) to be able to detect and follow the very earliest stages in the process of oxidation; and (3) to possess the means of comparing the potential keeping qualities of any two or more fats. Since no existing methods satisfy these requirements a new test for rancidity has been devised. (Lea, 1929). A New Test for Rancidity . Briefly, the process consists in heating the oil or fat with a solvent mixture of glacial acetic acid and chloroform in the presence of solid potassium iodide. Oxidation of the reagent or fat during the process is prevented by previously filling the tube with nitrogen, while the steady evolution of chloroform vapour effectively prevents diffusion of oxygen back into the tube. The reaction mixture is cooled, poured into 5 per cent. potassium iodide, and titrated with N/500 sodium thiosulphate solution.