Analysis of conjugated linoleic acid isomers by 13C NMR spectroscopy

The conjugated linoleic acids (CLAs), octadeca-10E, 12Z-dienoic and octadeca-11Z, 13E-dienoic acids, have been identified by 2D NMR spectroscopy in simple fatty acid mixtures. Unequivocal assignments for reporter resonances in the C-13 NMR spectra of these molecules are given. NMR assignments for the olefinic carbons of octadeca-8E,10Z-dienoic acid have also been obtained, along with full C-13 assignments for the octadeca-9,11-dienoic acids (ZE, ZZ and EE isomers). These data have been used to interpret the C-13 NMR spectrum of a complex CLA mixture, allowing the olefinic carbon chemical shifts of all isomers of 7,9 to 11,13 CLAs to be deduced. A method for the quantification of these compounds by C-13 NMR is described, demonstrating the utility of C-13 NMR spectroscopy in the analysis of complex CLA mixtures. (C) 1999 Elsevier Science Ireland Ltd. All rights reserved.