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.