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

Retief, Liezel (2006-12)

Thesis (MSc) -- University of Stellenbosch, 2006.

Thesis

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 literature method which had been developed for the assignment of the 13C NMR spectrum of olive oil. As this method proved to be time consuming and did not allow for the complete assignment of the oils a new rapid and potentially generic graphical method for 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 spectra where significant peak overlap occurs. The method has been validated by using it to assign the 13C NMR spectrum of olive oil which has been extensively reported in the literature. Concentration studies have also proved that the method is independent of the concentration of the oil used thus contributing to its general applicability. Quantification of the major fatty acid components of the six vegetable oils was also carried out using 13C NMR spectroscopy and the results obtained were compared with those obtained from gas-liquid chromatographic studies. This study showed that 13C NMR spectroscopy has use in quantifying the major fatty acid components of a variety of vegetable oils though is limited in that the minor fatty acid residues can not be detected reliably. Finally, due to the fact that resonances were detected in the 13C NMR spectra of the six vegetable oils indicating the presence of free fatty acids, a titration method was also developed for the six vegetable oils to determine the percentages of these free fatty acids. As the quantity of free fatty acids in a vegetable oil is often an indication of the quality of that oil, the development of such a technique has potential use in the quality control of the oils studied. Carrying out these titrations proved more difficult than expected, however a suitably reliable procedure has been developed and is documented here.

AFRIKAANSE OPSOMMING: Die doel van hierdie studie was om ses plaaslik geproduseerde groente olies (perske neut, avokado, druiwesaad, macadamia neut, mango neut and maroela olies) deur middel van 13C Kern Magnetiese Resonansie (KMR) spektroskopie te ontleed met betrekking tot hul hoof vetsuur komponente. Die eerste paging om hierdie olies te ontleed was gebaseer op 'n metode wat in die literatuur beskryf gebruik word vir die 13C KMR spektra van olyf olies. Die metode was egter tydrowend en oneffektief vir die identifikasie van elke piek in die 13C KMR spektra en gevolglik is 'n nuwe vinnige en generies grafiese metode ontwikkel vir die volledige identifikase van die 13C KMR spektrum van groente olies. Die metode is veral effektief vir areas in die 13C KMR spektrum waar piek oorvleueling voorkom. Die metode is geldig gemaak deur dit toe te pas op die 13C KMR spectrum van olyf olie wat reeds volledig beskryf is in die literatuur. Konsentrasie studies het oak aangedui dat die metode onafhanklik is van die konsentrasie van die olie wat dus bydrae tot sy algemene toepaslikheid. Kwantifikasie van die hoof vetsuur komponente teenwoordig in die ses olies is oak gedoen met behulp van 13C KMR spektroskopie waarvan die resultate vergelyk is met die van gas-vloeistof chomatografie studies. Daar word gewys dat 13C KMR spektroskopie gebruik kan word vir die kwantifikasie van die hoof vetsuur komponente vir 'n verskeidenheid van groente olies, maar dit is egter beperk in die sin dat dit nie doeltreffend tussen ander vetsuur komponente, wat teenwoordig is in minder hoeveelhede, kan vasstel nie. Laastens, as gevolg van die feit dat daar pieke opgetel is wat die teenwoordigheid van vrye vetsure in die 13C KMR spektra van die ses groente olies aandui, is 'n titrasie metode ontwikkel om die persentasies van hierdie vrye vetsure in die ses groente olies te bepaal. Die hoeveelheid vrye vetsure in groente olies is gewoonlik 'n aanduiding van die kwaliteit van die olie en het die ontwikkeling van so 'n tegniek gevolglik groat potensiaal in die kwaliteitsbeheer van die olies wat bestudeer is. Alhoewel die uitvoer van hierdie titrasies moeiliker was as verwag, is 'n gepaste betroubare prosedure ontwikkel en word hierin opgeteken.

Please refer to this item in SUNScholar by using the following persistent URL: http://hdl.handle.net/10019.1/50619
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