Use of 13C NMR Spectroscopy for Determination of Lipid Oxidation

Abstract

Although 13C NMR spectroscopy is not as frequently used as 1H NMR spectroscopy, it is a very powerful tool to elucidate the molecular structure of a compound, especially when it is used with 1H NMR spectroscopy. The chemical shifts of 13C NMR signals are quite characteristic for specific carbons. Other techniques involving 13C NMR such as two dimensional (2D) NMR techniques (e.g. 1H-13C heteronuclear single-quantum correlation spectroscopy (HSQC)), distortionless enhancement by polarization transfer (DEPT), and attached proton test (APT) are very useful tools to elucidate molecular structure of an organic compound. Therefore, the 13C NMR spectroscopy and related techniques have been used for analyses of foods and lipids. In many cases, 13C NMR is used along with 1H NMR since a 13C NMR spectrum is typically obtained from the same sample used for 1H NMR. Examples of the application of 13C NMR including distinguishing cis- and trans- isomers of a mono-unsaturated fatty acid, the determination of the fatty acid position in a triacylglycerol, simultaneous quantitative determinations of free fatty acids, contents of triacylglycerols and phospholipids, and fatty acid composition, the elucidation of the mechanism of lipid oxidation, the prediction of the stability of the non-polar portion of vegetable oil, and the detection of Diels-Alder products in oxidized oil are discussed in this chapter.