A novel approach to the rapid assignment of 13C NMR spectra ofmajor components of vegetable oils such as avocado, mango kernel andmacadamia nut oils

Abstract

Assignment of 13C nuclear magnetic resonance (NMR) spectra of major fatty acid components of South African produced vegetable oils was attempted using a method in which the vegetable oil was spiked with a standard triacylglycerol. This proved to be inadequate and therefore a new rapid and potentially generic graphical linear correlation method is proposed for assignment of the 13C NMR spectra ofmajor fatty acid components of apricot kernel, avocado pear, grapeseed,macadamia nut, mango kernel and marula vegetable oils. In this graphical correlation method, chemical shifts of fatty acids present in a known standard triacylglycerol is plotted against the corresponding chemical shifts of fatty acids present in the vegetable oils. This new approach (under carefully defined conditions and concentrations) was found especially useful for spectrally crowded regions where significant peak overlap occurs and was validated with the well-known 13C NMR spectrum of olive oil which has been extensively reported in the literature. In this way, a full assignment of the 13C{1H}NMRspectra of the vegetable oils, aswell as tripalmitolein was readily achieved and the resonances belonging to the palmitoleic acid component of the triacylglycerols in the case of macadamia nut and avocado pear oil resonances were also assigned for the first time in the 13C NMR spectra of these oils. © 2009 John Wiley & Sons, Ltd.