The determination of cis and trans fatty acid isomers in partially hydrogenated plant oils

Marais, Christiaan De Wet (2007-03)

Thesis (MSc (Chemistry and Polymer Science))--University of Stellenbosch, 2007.


Trans isomers are formed during the partial hydrogenation process of cis unsaturated fatty acids. The major source of trans fatty acids in the normal person's diet is from margarines and shortenings made from these partially hydrogenated plant and marine oils. In addition to influencing lipid risk factors for cardiovascular disease, trans fatty acids have also been implicated in breast cancer, and in poor fetal development and reduced early infant growth. In reality, trans fatty acids have been consumed for centuries, since they occur naturally in beef, mutton, butter, milk and other dairy products. Though it has been shown that these naturally occurring trans fatty acids have different effects on the health of humans. With the implementation of the new labelling law in South Africa, the trans fatty acids content of food items must be displayed on the food label. Therefore, it becomes necessary to optimise the analytical methodology for the determination of trans fatty acids in foods. Many publications have reported on the quantification of the total concentration of trans fatty acids in food samples, while less work has been done on the identification and quantification of the different cis and trans unsaturated fatty acid isomers found in foods made from partially hydrogenated oils. The objective of this study was to standardise and optimise an analytical technique to identify and quantify the different cis and trans mono-unsaturated fatty acid isomers in local margarines and bread spreads. Seeing that fatty acids are the group of lipids most commonly analysed by GLC and the availability of highly polar capillary columns bonded with cyanoalkyl polysiloxan phases, it was decided to use GLC for the identification and quantification of the different cis and trans isomers in a selected group of margarines. It was further decided to evaluate two BPX-70 capillary columns packed with cyanoalkyl polysiloxan phases. The one a 30 m BPX-70 capillary column, normally used for routine fatty acid analyses, and the other a 120 m BPX-70 capillary column.

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