Dialkyl Carbonate-Induced Transesterification for Analysis of Fatty Acids in Milk

A procedure is described whereby the alkyl esters of fatty acids may be prepared for gas-liquid chromatography (GLC) by a transesterification reaction applied directly to extracts of milk. To prepare the methyl esters the milk is extracted with a reagent consisting of methanol, dimethyl carbonate, and benzene. A portion of the clear extract is made alkaline by addition of sodium methoxide and the methyl esters are formed from the chemically bound (glyceryl and steryl) fatty acids in 1-2 nfin at room temperature. The mixture may be analyzed by GLC immediately. However, free fatty acids present are not esterified under these conditions. These may be subsequently esterified, at room temperature, by acidification of the reaction mixture. This forms the basis for a differential procedure for determination of free and chemically bound fatty acids in a mixture containing both.