Preparation of Methyl Esters of Fats and Oils by the Sealed Tube Method

Abstract

Traces of moisture in milkfat may prevent ester formation when using the sealed tube method. When dry fat is used transesterification was completed after heating 1 hour at 60 or 105°C as evidenced by analysis of the reaction products by thin layer chromatography. Methyl esters of highly saturated fats are not soluble in the reagent, addition of benzene to the reaction mixture resulted in satisfactory transesterification.In a recent review by Jensen et al. (1967) on the gas chromatographic analysis of milk fatty acids it was stated that many approaches to the problem of esterification have been described and that none of these is entirely satisfactory. In this laboratory we have used the sealed tube method of methyl ester preparation (deMan, 1964, 1967) in which the fat is esterified with 0.025N sodium methoxide in methanol With complete satisfaction. Among the advantages of this method is the minimum of time and materials involved and the prevention of losses of the volatile fatty acid esters. The method has been compared with two other common procedures and found superior for use with milkfat (deMan, 1967). A recent report by Storry et al. (1967) indicated that complete esterification is not always obtained with the method as outlined by deMan (1964). To investigate the possibility of incomplete esterification an investigation was made of the conditions of this method of ester preparation with milkfat and a number of other fats and oils.