Correlation between ¹H NMR and traditional methods for determining lipid oxidation of ethyl docosahexaenoate

Abstract

Abstract Lipid oxidation includes a complex set of chemical reactions; and no single analytical method is available to give a satisfactory description of lipid oxidation status. High‐resolution NMR spectroscopy techniques were tested to establish possible correlations with traditional analytical methods and to study lipid oxidation products. Ethyl esters of all‐ cis 4,7,10,13,16,19‐docosahexaenoic acid (DHA) (22∶6n−3), with and without added α‐tocopherol, were oxidized in the dark at 25°C in an air‐circulating oven. Correlations were found between primary oxidation products (PV and conjugated dienes) and the appearance of peaks in the 8.0–10.5 ppm chemical shift region of the 1 H NMR spectra. Multivariate data analysis (partial least squares; principal component regression) and the study of specific regions of the spectra obtained made it possible to easily separate samples of esters with and without α‐tocopherol based on the oxidation products formed. Based on knowledge about lipid oxidation products formed in marine lipids, selected oxidation products have been studied in the 1 H NMR spectra with the aim of finding detection limits and their chemical shift values.