Date of Award

2012

Document Type

Thesis

Publisher

Edith Cowan University

Degree Name

Doctor of Philosophy

School

School of Natural Sciences

Faculty

Faculty of Computing, Health and Science

First Supervisor

Dr Mary C. Boyce

Second Supervisor

Associate Professor Michael C. Breadmore

Abstract

Capillary electrophoresis (CE) has been used increasingly more over the last decade in the area of food analysis. Numerous food products and food components have been analysed using this technique because of its high efficiency and short separation times. However, the inherent lack of detection sensitivity in CE combined with the complex matrices present in many food samples, especially those of plant origins, is one of the contributing factors to the limited development on CE in this particular area of food analysis. In this project, the potential of CE as a tool in the analysis of vegetables belonging to the family Brassica oleracea was investigated. Capillary zone electrophoresis (CZE), the most frequently used CE mode in food analysis, has been employed to quantitatively determine the phenolic acids present in vegetables of B. oleracea. A simple and rapid CZE method for the baseline resolution of four hydroxycinnamic acids was developed. Peak efficiencies and separation time were optimised by adjustment of the borate buffer concentration (15 mM sodium tetraborate pH 9.13) with the optimum method having a separation time of 7 min with detection limits ranging from 1.1 to 2.3 mg/kg of vegetables. The developed CZE method was applied to resolve the key flavonoids in broccoli extracts, however, detection sensitivity was poor for these compounds. To overcome this limitation an online pre-concentration method, large volume sample stacking (LVSS), was used to enable quantitative determination of flavonols in broccoli. This LVSS-CZE method allowed for the separation of two flavonols, kaempferol and quercetin, within 8 min with average enhancement factors of approximately 20 when compared to the original CZE method, giving detection limits of 0.6 and 0.9 mg/kg of broccoli. Resolution of the two flavonols was optimised by varying the borate buffer concentration and pH (the optimum values are 10 mM sodium tetraborate pH 8.40) and by using a longer capillary (85 cm). Different LVSS parameters including stacking voltage and sample injection times were also investigated. Micellar electrokinetic chromatography (MEKC), the second most commonly employed CE mode in food analysis, was used for the quantitative determination of glucoraphanin, a predominant glucosinolate in broccoli. A MEKC system was developed in which the surfactant, sodium cholate was used as the pseudo stationary phase and separation of glucoraphanin was achieved in less than 5 min with detection limits ranging from 0.1 to 4 mg/100g of vegetables or seeds. Furthermore, and as a direct result of the requirement for a glucoraphanin standard, a preparative HPLC experiment was devised for the undergraduate chemistry program within Edith Cowan University. All the developed CE methods were validated with repeatability studies and linearity measurements and then successfully applied to the quantitative determination of the target analytes in a range of B. Oleracea vegetables and seeds. The accuracy of the CE quantitative data was ascertained by comparison to those from HPLC analysis.

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