Reliability of 1H NMR Analysis for Assessment of Lipid Oxidation at Frying Temperatures

Abstract

AbstractThe reliability of a method using 1H NMR analysis for assessment of oil oxidation at frying temperatures was examined. During heating and frying at 180 °C, changes of soybean oil signals in the 1H NMR spectrum including olefinic (5.16–5.30 ppm), bisallylic (2.70–2.88 ppm), and allylic (1.94–2.15 ppm) proton signals relative to glyceride backbone CH2 (5.30–5.46 ppm) and aliphatic CH2 (1.05–1.71 ppm) signals showed strong correlations with conventional analytical methods including total polar compounds, polymerized triacylglycerols, and changes of linoleic acid and linolenic acid peaks in gas chromatography. For oils rich in oleic acid, mid‐oleic sunflower oil (NuSun) and high oleic soybean oil, only the olefinic and allylic proton signals are recommended for analysis due to the relatively low intensity of the bisallylic proton signal. Under these heating and frying conditions, signals indicating intermediate oxidation products, hydroperoxides, were not detected while very small signals corresponding to a variety of aldehydes including alkanal, branched alkenal, 2‐alkenal, and aldehydes of conjugated dienes and epoxides were observed. In this study, it was found that the 1H NMR method is a fast, convenient, and reliable analytical method to determine the oxidation state of frying oil.