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A. P. REID¹, D. Cantellops², D. R. EITENMILLER³, E. Bonnin², and A. R. Long⁴. (1) Atlanta Center for Nutrient Analysis, U.S. Food and Drug Administration, 60 8th St. N.E., Atlanta, GA 30309, (2) Chemistry Branch, Drug Group, (3) Department of Food Science and Technology, University of Georgia, Athens, GA 30602, (4) Pacific Region Laboratory, U.S. Food and Drug Admininstration, 22201 23rd Drive S.E., Bothell, WA 98041

The U.S. Food and Drug Admin. is proposing to amend its regulations on nutritional labeling to require that the amount of trans fat in foods and dietary supplements be included. A need exists for a fast and reliable method to determine cis-trans isomeric fatty acids. However, most methods lack resolution and identification of complex mixtures of cis-trans isomers.

The objective of this work was to apply a recently published direct extraction/methylation (DEM) procedure coupled to capillary gas chromatography on a 100-meter silica column to the identification and quantification of trans isomers in infant formula and margarine.

The approach used in this work is based on the DEM procedure described in Cantellopes et. al. 1999, using direct addition of sodium methoxide/hexane and heating to simultaneously extract and trans-esterify acyl lipids to FAMEs. The temperature and pressure programming is suited to the 100-meter column to achieve maximum separation of peaks.

The overall method was applied to NIST SRM 1846 (powdered, milk based infant formula) and a commercial margarine. The following trans isomers were identified in both samples: C18:1 T-6, C18:1 T-9, C18:1 T-11, and C18:1 T-12. Trans FAMEs were quantified over a concentration range of 0 to 1.0 mg/mL (r > 0.9993). Reproducibility was constant at each fatty acid level in the reaction mixture (n=10, %CV < 2%) for each sample matrix. The amount of trans fat found in SRM 1846 was 43.5mg/g and 138.4 mg/g for the margarine.

The DEM procedure, together with capillary GC, provides excellent resolution of trans isomers and improves our ability to positively identify and quantify the cis-trans isomers in food matrices (including minor peaks). The method can be easily interfaced with GC-MS to improve identification of resolved cis-trans fatty acids.