Systematic isolation and identification of minor components in heated and unheated fat

Abstract

Although animal studies have shown that the chemical reactions occurring in fats during frying do not make them unsuited for food use, questions continue to arise about the products of these reactions and their significance. The purpose of this work was to identify as many as possible of the monomeric products that form when fats are heated in the air. Cottonseed oil was kept at 182 C for six 8 hr days; then it was converted to methyl esters. The distillable, non-urea-adductable fraction (DNUA) of the esters was separated into 96 fractions by gradient elution chromatography on silica gel. Each fraction was analyzed by gas liquid chromatography (GLC). One hundred thirty-six components were observed, corresponding to 0.42% of the fat. Many of the components were isolated by preparative GLC. Fifty-one were partially or completely characterized. The most abundant components of the DNUA were octadecenoate and octadecadienoate which had not been removed completely by urea adduction. Esters of alicyclic fatty acids made up 34% of the characterized material. These cyclic materials are probably responsible for the toxic effects that have been seen when DNUA was isolated and fed to rats at high dietary levels. Many of the other components appear to be of little biological interest. No components present in substantial amounts remain uncharacterized.