DEFINITION
This method provides a gas–liquid chromatography (GLC) procedure for the determination of the fatty acid composition, including the trans fatty acid isomers of extracted fats. The fatty acid methyl esters (FAME) are separated on a capillary gas chromatography column having a highly polar stationary phase, according to their chain length (CL), degree of unsaturation, and geometry and position of the double bonds [DB(s)].

SCOPE
This method evaluates, by a single capillary GLC procedure, the levels of trans isomers, saturated fatty acid (SFA), cis- and trans-monounsaturated fatty acid (MUFA), and cis- and trans-polyunsaturated fatty acid (PUFA) in fat samples where the source of the fat is unknown or is of dairy or ruminant origins. The method is not designed to provide detailed definitive isomer composition that may be desired for nutritional and/or biochemical purposes. To obtain more detailed isomeric composition information prior argentation chromatographic separations and/or additional GC analyses are required. For nutritional labeling purposes the total fat, saturated, cis-monounsaturated, cis-polyunsaturated and trans fatty acid contents are to be determined. This method may also determine cis-polyunsaturated fatty acids (PUFA), including arachidonic acid (AA), eicosapentaenoic acid (EPA), and docosahexaenoic acid (DHA).

This method utilizes a triacylglycerol (13:0 TAG) internal standard (IS) for determining the concentration of the individual fatty acids in the oil samples after methylation. The method is applicable to fats derived from dairy and ru-minant products. This method is not applicable to products containing mixtures of both dairy and vegetable fats as the trans linolenic acid (18:3) isomers will coelute with the gondoic acid (20:1) isomers. In that case both this method cou-pled with AOCS Ce 1h-05 would be required for analysis. Conjugated linoleic acids (CLAs) will be present in dairy and ruminant fats and may be quantitated with this method, however for nutritional labeling purposes CLA are not in-cluded either as cis- or trans-PUFA (References 1 and 2). There is minor coelution of cis- and trans-fatty acid isomers, particularly in the 16:1, 17:1, and 18:1 regions, using this technique. Theoretical Correction Factors (TCFs) are used to quantitate all saturated, monounsaturated, and polyunsaturated fatty acids (PUFA) of 18 carbons. TCFs are also used for fatty acids, which lack pure standards. Empirical Correction Factors (ECFs) are used for very long chain PUFA of 20 carbons or more and three or more double bonds for which standards are readily available.