NMR analysis
Oil oxidation was evaluated with the previously reported NMR method
(Hwang et al., 2017). Oil samples were dissolved in
CDCl3, and spectra were taken with a Bruker Avance 500
spectrometer (Bruker Biospin, Billerica, MA, USA). Signals were analyzed
with SpinWorks 4 software (Chemistry NMR Lab, Winnipeg, MB, Canada).
Signal intensities of olefinic protons (olefinic H) at 5.29-5.46 ppm,
bisallylic protons (bisallylic H) at 2.70-2.88 ppm, and
allylic protons (allylic H) at
1.94–2.15 ppm were determined. While olefinic H and bisallylic H were
used to assess the oxidation of SBO and corn oil because these two
signals had biggest changes during oxidation, the loss of allylic H was
used in place of bisallylic H for high oleic oils including olive oil,
canola oil, HO SBO, and avocado oil because their bisallylic H signals
were too small.