The application of NMR in compositional and quantitative analysis of oils and lipids

Abstract

This chapter reviews the use of NMR for compositional and quantitative analysis of oils and lipids in food. The literature of the past decade on the following topics is reviewed: High-resolution 13 C NMR is a powerful method to determine the positional distribution of different classes of fatty acids on the glycerol backbone due to chemical shift differences observed on the carbonyl signal. Oxidation products such as aldehydes, hydroperoxides, and epoxides can be observed and quantified directly in the 1 H NMR spectrum of lipids. Results agree very well with classical methods such as determination of anisidine value and peroxide value. The advantage of NMR lies in the additional information obtained and the ease of sample preparation and the speed of the analysis in general. Minor components of oils and lipids such as sterols, polyphenols, and glycerol can be quantified either directly or after derivatization. In addition, conjugated fatty acids and galactolipids are observed. By means of 31 P NMR, it is possible to identify and quantify all known phospholipids using various extraction or preconcentration methods. Also, the concentration of diglycerides and monoglycerides in the lipid matrix can be determined in a straightforward way without timeconsuming sample pretreatment. High-resolution 1 H NMR is also a very useful technique to obtain information on the fatty acid composition of oils, albeit more restricted to classes of fatty acids: saturated, monounsaturated, and polyunsaturated. Such information can also be obtained by means of low-field NMR when combined with chemometric methods. Time-domain NMR, finally, is a fast and cost-effective method to assess total lipid content and water content and to obtain information on the physical state of these components.