New <sup>1</sup>H NMR-Based Technique To Determine
Epoxide Concentrations in Oxidized Oil
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Abstract
A new method to determine epoxide
concentrations in oxidized oils
was developed and validated using <sup>1</sup>H 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 <sup>1</sup>H NMR by taking the <i>sn</i>-1,3 glycerol protons (4.18, 4.33 ppm) as internal references. The <sup>1</sup>H 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
(<i>R</i><sup>2</sup> = 99.96%), and validation of the method
gave results comparable to those of the HBr method. A study of the
oxidative stability of soybean oil 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