Abstract
Normal-phase high-performance liquid chromatography (HPLC) is widely used in combination with evaporative light scattering detection (ELSD) for separating and detecting lipids in various food samples. ELSD responses of different lipids were evaluated to elucidate the possibilities and challenges associated with quantification by means of HPLC-ELSD. Not only the number and type of polar functional groups but also the chain length and degree of unsaturation of (free or esterified) fatty acids (FAs) had a significant effect on ELSD responses. Tripalmitin and trilinolein yielded notably different ELSD responses, even if their constituting free FAs produced identical responses. How FA structure impacts ELSD responses of free FAs is thus not predictive for those of triacylglycerols and presumably other lipids containing esterified FAs. Because ELSD responses of lipids depend on the identity of the (esterified) FA(s) which they contain, fully accurate lipid quantification with HPLC-ELSD is challenging and time-consuming. Nonetheless, HPLC-ELSD is a good and fast technique to semi-quantitatively compare the levels of different lipid classes between samples of comparable FA composition. In this way, lipid profiles of different flours from near-isogenic wheat lines could be compared.
Highlights
Received: 10 January 2021There is no widely accepted definition for the term “lipids” as it needs to cover an extremely broad variety of natural compounds
As observed by Jones and coworkers [22] and Donot and coworkers [21], the evaporative light scattering detection (ELSD) responses decreased in the order free FAs (FFAs), DAGs and MAGs and were not related to lipid molecular weight
That chain length and degree of unsaturation of acyl constituents do not appear to have a significant effect on ELSD response [29,32], our findings are in agreement with those of other authors who noticed different ELSD responses for different TAG molecular species [32,71]
Summary
Received: 10 January 2021There is no widely accepted definition for the term “lipids” as it needs to cover an extremely broad variety of natural compounds. In naturally occurring lipids (of plant and animal origin), FAs are mostly esterified to glycerol or other alcohols (such as cholesterol) or linked by amide bonds to long-chain bases (sphingoids or bases thereof) or, exceptionally, to other amines. They may contain carbohydrates, phosphoric groups and/or organic bases [2,3]. Simple lipids such as the glycerol esters of FAs are composed of only two different types of structural moieties, whereas complex lipids have more than two types of structural moieties. Trilinolein and tripalmitin, e.g., both belong to the class of the triacylglycerols (TAGs)
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