NMR Spectroscopy for Evaluation of Lipid Oxidation

During storage and use of edible oils and other lipid-containing foods, reactions between lipids and oxygen occur, resulting in lipid oxidation and the subsequent development of off-flavors and odors. Accurate and timely assessment of lipid oxidation is critical for effective quality control of food products. NMR spectroscopy techniques including 1H, 13C, and 31P NMR have been used to determine the oxidation stage and quality of lipids, to elucidate chemical structures of oxidation products, and to verify oxidation mechanisms. NMR spectroscopy methods have been successfully employed to identify oxidation products, including primary oxidation products such as hydroperoxides and conjugated dienes and secondary products such as aldehydes, alcohols, epoxides and their derivatives. 1H NMR can also be used to determine the extent of lipid oxidation during frying and storage by monitoring the decrease in peak area of protons located in reactive sites of oil molecules including olefinic, bisallylic and allylic protons. 13C NMR has been used to identify oxidation products along with 1H NMR, gas chromatography-mass spectroscopy (GC-MS) and other methods. 31P NMR also has been utilized to assess the oxidation of edible oils along with 1H and 13C NMR spectroscopies. These methods correlate well with traditional methods and offer highly reliable, non-destructive, fast analysis of lipid oxidation. These analytical methods will be summarized in this chapter.

Keywords: Conjugated diene, 13C NMR, Diels-Alder reaction, DEPT, Frying, Hydroperoxide, 1H NMR, Lipid oxidation, NMR spectroscopy, Oxidation products, 31P NMR.