HPLC and capillary electrophoresis of bioactive compounds in food matrices of plant origin: fundamental and practical aspects

This communication discusses the results of our recent studies carried out to investigate a variety of factors that influence both electrophoretic and chromatographic behaviour of bioactive compounds extracted from plant tissues and food matrices of plant origin. Most of these compounds are secondary metabolites produced within the plants besides the primary biosynthetic and metabolic routes. They hold various types of important functions in plant tissues, such as protection, attraction or signalling, and most of them, which are present as "non-nutritive" compounds in plant food, have found to play an important role in disease prevention and health-promoting effects. The presentation evaluates the influence of the composition of either the electrolyte solution (BGE) or the mobile phase on the selective separation of the above compounds in capillary zone electrophoresis (CZE) and RP-HPLC, respectively. Appropriate selection of the chemical composition of either the BGE in CZE or the mobile phase in RP-HPLC involves the evaluation of the equilibrium in solution that might take place between the analytes and the components of such solutions. In addition, the chemical composition of the liquid phase affect the physical-chemical properties of the separation medium, such as pH, ionic strength and surface tension, which, in both techniques, might influence the separation performance to different extents. The incorporation of organic solvents into either the BGE or the mobile phase also has a strong impact on both electrophoretic and chromatographic behaviour of the bioactive compounds found in food matrices of plant origin, which, in most cases, are complex molecules bearing a variety of functional groups. Moreover, ionic and non-ionic components of the BGE influence the generation of the electric double layer at the interface between the inner surface of fused silica capillaries and the electrolyte solution, which originates the electroosmotic flow in CZE. In conclusion, the potentiality of CZE and RP-HPLC in separating bioactive compounds in plant tissues and food matrices of plant origin is illustrated and the possibility of tailoring selectivity and efficiency of the considered separation systems by incorporating suitable buffering agents, organic solvents, and/or additives into the BGE or the mobile phase, respectively, is discussed.