Fatty Acids of the Total Lipids from Earthworms

The total lipids extracted from earthworms were converted to fatty acid methyl esters, and the esters were analyzed to examine their composition by capillary gas chromatography. In the gas chromatogram over 100 peaks were observed, indicating the presence of at least 100 kinds of fatty acids. On the basis of comparison with cochromatographed standards and of argentation thinlayer chromatographic behaviors, a series of saturated fatty acids(12:0, 13:0, 14:0, 15:0, 16:0, 17:0, 18:0, 20:0, 22:0 and 24:0) and di- and polyunsaturated fatty acids(linoleic acid, α-linolenic acid, arachidonic acid, EPA, DHA, etc. )were determined. An aliquot of the fatty acid methyl ester mix- ture was then derivatized to dimethyl disulfide adducts, and the adducts were analyzed to locate the original double-bonds of the methyl monoenoates by gas chromatography/mass spectrometry. Based on the mass spectral evidence and mass chromatographic tracing, 41 kinds of double-bond positional isomers of the monounsaturated fatty acids were identified. Among them, the predominant component was cis-7-icosenoic acid which occupied 5.5% of the total fatty acids in the earthworm lipids. To our knowledge, cis-7-icosenoic acid is a novel fatty acid found in nature. Thus the earthworm lipids could be characterized due to the complexity of the fatty acid profile.