Analytical Methods for Quantification of Modified Fatty Acids and Sterols Formed as a Result of Processing
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Analytical Methods for Quantification of Modified Fatty Acids and Sterols Formed as a Result of Processing O. Berdeaux & P. C. Dutta & M. C. Dobarganes & J. L. Sébédio
Received: 22 May 2008 / Accepted: 9 October 2008 / Published online: 29 October 2008 # Springer Science + Business Media, LLC 2008
Abstract Fats and oils are often submitted to technological treatments before being consumed. Some treatments like refining, hydrogenation, and frying often lead to the formation of modified fatty acids such as cyclic fatty acid monomers (CFAM), geometrical fatty acid isomers, and/or oxidized fatty acids and sterols (cholesterol and phytosterols). Both cholesterol oxidation products (COP) and phytosterol oxidation products (POP), may be present in foods. As some of the newly formed components may present some adverse effects upon consumption, methods have been developed to analyze these compounds in food products and biological samples. Gas liquid chromatography (GC) on long polar columns (100m) is a good choice to quantify trans mono- and polyunsaturated fatty acids. In some cases a pre-fractionation step using silver nitrate thin layer chromatography (AgNO3-TLC) may be necessary to avoid GC overlapping of cis and trans isomers. Analysis of CFAM usually involves transformation O. Berdeaux (*) Plateforme “lipides-arômes”, UMR FLAVIC, INRA-ENESAD-Université de Bourgogne, 17 rue Sully, BP86510, 21065 Dijon Cedex, France e-mail: [email protected] P. C. Dutta Department of Food Science, Swedish University of Agricultural Sciences, Uppsala, Sweden M. C. Dobarganes Instituto de la Grasa (CSIC), Avenida Padre Garcia Tejero 4, 41012 Seville, Spain J. L. Sébédio Plateforme d’exploration du métabolisme, des gènes aux métabolites, Laboratoire de Nutrition Humaine, UMR 1019, INRA-Université d’Auvergne, St Genès Champanelle 63122, France
of the sample in fatty acid methyl esters (FAME) which after addition of an internal standard (IS) are further hydrogenated. An enrichment step using reverse phase high performance liquid chromatography (RP-HPLC) permits to obtain a fraction which consists of a mixture of CFAM and the IS. This fraction is further analyzed by GC on a polar column. The analysis of oxidized triacylglycerol monomers (oxTG) as a group was feasible by a combination of adsorption and sizeexclusion chromatography. Quantification in used frying fats and oils around the limit of rejection for human consumption (25% polar compounds) has shown that the amount of oxTG range 5.9–9.4% expressed on fat or oil weight. In foods and biological tissues, the level of oxidized sterols (SOP) is often a very small fraction of their unoxidized forms. Analysis of SOP involved extraction of lipids, saponification or transesterification, enrichment, and subsequent qualitative and quantitative determination by GC and GC-MS, or HPLC and HPLC-MS. In addition, enrichment of SOP requires complete separation from the unoxidized sterols in order to separate these compounds even by high resolution GC capillary columns. Keywords Heat Treatment . Ox
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