New 1H NMR-Based Technique To Determine Epoxide Concentrations in Oxidized Oil

A new method to determine epoxide:concentrations in oxidized oils Was developed and validated using H-1 NMR. Epoxides derived from lipid oxidation gave signals between 2.90 and 3.24 ppm, well separated from the signals of other lipid oxidation products. To calibrate, soybean, oils with a range of epoxide concentrations were synthesized and analyzed using NMR by taking the sn-1,3 glycerol protons (4.18, 4.33 ppm) as internal references. The NMR signals were compared to the epoxide content determined by titration with hydrogen bromide (HBr)-acetic acid solution. As expected, the signal response increased with concentration linearly (R-2 = 99.96%), and validation of the method gave results comparable to those of the HBr method. A study of the oxidative stability of soybean off was performed by applying this method to monitor epoxides during thermal lipid oxidation. The epoxide content increased over time and showed a different trend compared to peroxide value (PV). A phenomenological model was suggested to model epoxides derived from lipid oxidation.