Major component determination of selected vegetable oils by means of qualitative and quantitative ¹³C NMR spectroscopy

[摘要] ENGLISH ABSTRACT: The aim of this study was to assign the 13C Nuclear Magnetic Resonance (NMR)spectra of the major fatty acid components of six locally produced vegetable oils(apricot kernel, avocado, grapeseed, macadamia nut, mango kernel and marula oils).A first attempt at the assignment of the spectra involved the use of a literaturemethod which had been developed for the assignment of the 13C NMR spectrum ofolive oil. As this method proved to be time consuming and did not allow for thecomplete assignment of the oils a new rapid and potentially generic graphical methodfor the full assignment of the 13C NMR spectra of the vegetable oils was developed.The method was shown to be especially useful for regions of the 13C NMR spectrawhere significant peak overlap occurs. The method has been validated by using it toassign the 13C NMR spectrum of olive oil which has been extensively reported in theliterature. Concentration studies have also proved that the method is independent ofthe concentration of the oil used thus contributing to its general applicability.Quantification of the major fatty acid components of the six vegetable oils was alsocarried out using 13C NMR spectroscopy and the results obtained were comparedwith those obtained from gas-liquid chromatographic studies. This study showed that13C NMR spectroscopy has use in quantifying the major fatty acid components of avariety of vegetable oils though is limited in that the minor fatty acid residues can notbe detected reliably.Finally, due to the fact that resonances were detected in the 13C NMR spectra of thesix vegetable oils indicating the presence of free fatty acids, a titration method wasalso developed for the six vegetable oils to determine the percentages of these freefatty acids. As the quantity of free fatty acids in a vegetable oil is often an indicationof the quality of that oil, the development of such a technique has potential use in thequality control of the oils studied. Carrying out these titrations proved more difficultthan expected, however a suitably reliable procedure has been developed and isdocumented here.

[发布机构] Stellenbosch University