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Dialkyl Carbonate-Induced Transesterification for Analysis of Fatty Acids in Milk^{1, 2,}

Department of Biochemistry, University of Minnesota, St. Paul

ABSTRACT

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 min 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.

Fatty acid ethyl, propyl, and butyl esters may be obtained in a completely analogous manner.

¹ Paper no. 5988, Scientific Journal Series, Minnesota Agricultural Experiment Station.

² This investigation was supported, in part, by Contract no. 12-14-100-7191 (74), United States Department of Agriculture and, in part, by public Health Service Grant EF-00089 from the Div. of Environmental Engineering and Food Protection.