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

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.

1H NMR spectroscopy as tool to follow changes in the fatty acids of fish oils

“…Similar findings for other edible oils have been reported previously [20]. The R AO value did not increase distinctly in setup 1 or 4, which is also in agreement with other studies [11]. The NMR signal of the bis-allylic methylene groups showed the same behaviour as the olefinic protons.…”

“…However, integrals over the signals indicated the content of these oxidation products to be very low. Previously reported amounts for such molecules were higher, which is likely caused by either higher temperatures and faster product accumulation or by oxidation of a single fatty acid instead of a complex mixture [11,23,24].…”

“…Igarashi et al [10] investigated the content of docosahexaenoic acid (DHA) and n-3 fatty acids in fish oils. Recently, the correlation between traditional methods and 1 H NMR for the determination of lipid oxidation of docosahexaenoic acid has been studied [11].…”

Isolation and characterization of a steroidal compound from the hexane extract of the leaves of Artabotrys odoratissimus

“…A broad singlet at δ 1.56 for beta methylene protons. A broad singlet at δ 1.26 assigned to rest of the methylene protons (Falch et al, 2004;Fauhl et al, 2000;Guillen and Ruiz, 2005;Guillen and Ruiz, 2003;Panico et al, 1994;Gunstone et al, 1975;Lie Ken Jie et al, 2003). C 13 NMR spectrum value were consistent with the proposed structure, it showed a peak at δ 173.8 for carbonyl carbon.…”

Determining nutritional labeling data for fats and oils by 1H NMR

“…Hence, it would clearly be preferable to employ high-resolution 1 H NMR spectroscopy, which offers the advantages of short relaxation times and high S/N, owing to the high natural abundance (>99%) of 1 H. Many applications of 1 H NMR spectroscopy in edible oil analysis have been investigated, including the characterization of oils in terms of their FA composition [7,[10][11][12][13][14][15][16][17][18], the assessment of oil quality [19,20] and authenticity [21,22], the study of lipid oxidation [23,24], and the assessment of varietal differences and geographical origin of oils [25]. However, as noted above, none of these studies have addressed the question of whether cis-and trans-unsaturation in fats and oils can be distinguished by 1 H NMR.…”