Lipid Analyses in Food
Published Online: 15 SEP 2006
Copyright © 2000 John Wiley & Sons, Ltd. All rights reserved.
Encyclopedia of Analytical Chemistry
How to Cite
Marini, D. 2006. Lipid Analyses in Food. Encyclopedia of Analytical Chemistry.
- Published Online: 15 SEP 2006
The term lipid encompasses a great host of compounds (e.g. fatty acids (FAs), mono-, di- and triglycerides), that are almost ubiquitously present in foods; their characterization and quantification is then of importance for an analytical chemist.
The first step for an accurate analysis is sample preparation: choosing an appropriate solvent or phases can isolate one particular class of lipid from a sample [a good separation of classes can be accomplised by thin-layer chromatography (TLC)]; obviously, the sample pretreatment will be governed by the determinations to follow. Indeed, nowadays, there is a host of techniques, mainly chromatographic, for lipid analysis. TLC is a rapid way to gather information about the sample (presence of conjugated double and triple bonds, free FAs and of oxygenated FAs), particularly with the development of modified normal phases. For example, silica gel can be impregnated with boric acid, which inhibits isomerization of mono- and diglycerides, or it can be treated with silver ions [argentation, for silver ion thin-layer chromatography (Ag-TLC)] used for resolution of unsaturated FAs. Gas chromatography (GC) and high-performance liquid chromatography (HPLC) are the most common techniques actually employed, because of their versatility (many parameters can be changed, e.g. stationary and mobile phases, detector) and to their capacity to be hyphenated (coupled with another measuring device). Particularly, the advent of the light-scattering detector has allowed greater reproducibility in the HPLC of lipids. Mass spectrometry (MS) is often coupled with GC. However, coupling MS with another MS (MS/MS or tandem MS) is useful for the determination of the structure of long-chain FAs with improved selectivity and sensitivity. Finally, nuclear magnetic resonance (NMR) is able to identify functional groups, even in mixtures, and is a valid aid for the elucidation of structures with double bonds (DBs) by interpretation of the coupling patterns.
Each analytical method relies on appropriate sample preparation (e.g. methylation for the GC analysis of FAs) and a critical approach to evaluate its usefulness.