Studies on the Oxidative Deterioration and the Coloration of Animal Fats

VI. Spectrophotometric Studies on the Oxidation of Butter Fats

Abstract

For the purpose of getting a more insight of the mechanism of the discoloration and the browning of butter fats during the oxidation, changes in the spectral characteristics occurring butter fats in the course of autoxidation and oxidation by heating were studied.
Fresh butter fats had the absorption maxima at 230, 270, 280, 302, and 317mμ in the ultraviolet absorption spectra and at 430, 455, and 482mμ in the visible region of the spectra. It was known that the absorption maxima in the visible and the ultraviolet regions of the spectra were produced by carotene pigments and sterols, respectively.
The absorption maxima of butter fats in the visible region disappeared prior to the begining of oxidation of the fats. The absorption maxima in the ultraviolet region disappeared gradually in the course of oxidation of the fats.
Conjugated diene and triene acids were contained about 1 and 0.02 per cent, respectively, in fresh butter fats. There was no difference in the content between these conjugated acids in butter fats in the course of autoxidation.
Autoxidized and colored butter fats and the oxidized-acid-free fractions of butter fats were studied for spectral characteristic. It was recognized that the coloration of fats resulted from the increase of absorption of light in a wide range from the ultraviolet to the visible regions in the absorption spectra of the fats.