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United States Department of Agriculture

Agricultural Research Service

Title: Simplifying Fatty Acid Analyses in Multicomponent Foods by Way of a Standard Set of Isothermal Glc Conditions Coupled with Ecl Determinations

Author
item Thompson Jr, Raymond

Submitted to: Journal of Chromatographic Science
Publication Type: Peer Reviewed Journal
Publication Acceptance Date: May 29, 1996
Publication Date: N/A

Interpretive Summary: Reliable and cost-effective methods are needed to identify and quantify the fatty acids in today's foods, in new crop varieties, and in newer fats and oils being developed. Fatty acids are the principal components of the fats and oils that influence a food's palatability, stability, functional characteristics, and nutritional properties. In addition, food-labeling regulations now require that fat contents be calculated from fatty acid analyses, not by measurement of constituents referred to as total-lipid. The practice of gas chromatography (GC) with capillary columns, now the basis of all modern fatty acid analyses, has not been well served by the multitude of GC methods presently being used, viz., different types of capillary columns, operated at many different temperatures. Heterogeneity of methods and practices diminishes the value of published data, complicates the collection of new data, and hinders summarization for databases of food composition. This work was undertaken to bring more order to the process, and it has: a "standard" column was identified; GC retention information has been obtained for a great many of the fatty acids encountered in the analysis of foods; and optimal GC column temperatures were established for analyses carried out on the "standard" column. The result is a simple protocol for chemists, food technologists and nutritional scientists to use to accurately identify individual fatty acids during chemical analysis of foods and other natural products.

Technical Abstract: It is very common to use some sort of temperature program in the analysis of fatty acid methyl esters. For samples containing only a few components or for situations where all samples are basically the same, temperature programming can offer certain advantages. Unfortunately, though, samples such as that are certainly not the norm in routine food fatty acid analysis. We have taken a particular type of GLC column the Carbowax-20M phase (cross-linked) in fused-silica recommended by R. G. Ackman as a "standard" for fatty acid analysis (it simplifies the work, and reduces the chance for errors) and chromatographed mixtures of methyl esters at column temperature settings ranging from 170 degrees to 250 degrees C. Three specific temperatures have been found (183 degrees, 212 degrees, and 247 degrees) that permit complete resolution of a very wide array of acids, under strictly isothermal conditions. ECL values have been compiled for use in assigning identities of fatty acid methyl esters. Also, the specific responses of individual methyl esters to alterations in column temperature can be of use in helping to identify the peaks in complex mixtures.

Last Modified: 9/21/2014