Eicosapentaenoic Acid Is Most Oxidatively Stable in the sn-2 Position of Triacylglycerols Compared with sn-3 and sn-1

Abstract

Eicosapentaenoic acid (EPA) is an omega-3 polyunsaturated fatty acid (PUFA), which is easily oxidized based on its high level of unsaturation. So far, it is not fully clear how the location of EPA in triacylglycerols (TAGs) affects its stability. Here, the oxidative stability of EPA in regio- and enantiopure TAGs was investigated for the first time. For analysis of the complete oxidation behavior at 50 °C, headspace solid-phase micro extraction with gas chromatography–mass spectrometry (HS-SPME–GC–MS), liquid chromatography–MS (LC–MS), and nuclear magnetic resonance (NMR) spectroscopy were used, and the data obtained with all used methods was examined in combination using multivariate analysis (oxidomics approach). Oxidation patterns of EPA-containing TAGs were similar as seen previously for docosahexaenoic acid (DHA)-containing ones as shown in the abundance of propanal, 1-penten-3-ol, 2,4-heptadienal, or 5-ethyl-2(5H)-furanone. EPA in sn-2 was clearly the most stable as seen earlier for neat oil of regiopure TAGs-containing EPA and other omega-3 PUFAs at sn-2 position. The stability of EPA in sn-1 and sn-3 was expected to be identical under the achiral conditions. However, a minor tendency for better stability of sn-3 compared with sn-1 was seen at certain time points, the difference most likely arising from differences in levels of minor undetected and unidentified prooxidants.

Practical Applications: On the basis of the results of this study, sn-2 should be highly favored for eicosapentaenoic acid in triacylglycerols to improve the stability of neat oils. This is of high interest for enzymatic restructuring processes of eicosapentaenoic acid-rich oils, such as those used for marine oil concentrates. By using enzymes with right regio- and enantiospecificity, the oxidative stability of omega-3 concentrates could be significantly improved over a randomized configuration of fatty acids in triacylglycerols. The findings in this study further contribute to knowledge on the formation of oxidation compounds from eicosapentaenoic acid as not all oxidation compounds reported in this study have been reported earlier. This will contribute to finding new solutions on how to analyze lipid oxidation in the future. Additionally, the reported experimental setup and oxidomic approach could be used to study other lipid species at different temperatures to achieve a complete picture on their oxidative behavior.