High performance separation techniques for identification, characterization and quantification of plant secondary metabolites with health-promoting properties

The wide range of bioactive compounds produced in plants by the secondary metabolism comprise food ingredients having disease prevention and health-promoting properties, in addition to give specific sensorial characteristics to the aliment. The identification and quantification of these target compounds in plants and agro-food matrices is a challenging task, continuously requesting the development of more robust, efficient and sensitive instrumental analytical techniques. This communication discusses fundamental and practical aspects of both reversed phase high performance liquid chromatography (RP-HPLC) and capillary zone electrophoresis (CZE) employed for the analysis of plant secondary metabolites occurring in food and cosmetic matrices. The two analytical separation techniques might display complementary capability in separating secondary metabolites, as it is discussed for the analysis of phenolic compounds in plant extracts. The different selectivity exhibited by RP-HPLC and CZE in separating phenolic compounds has been ascribed to the concomitant presence of hydrophilic, hydrophobic and ionogenic groups displayed by most of these compounds, which is expected to influence to different extents the separation mechanisms operating in CZE and in RP-HPLC of molecules bearing multifunctional moieties. The presentation discusses the influence of various operational parameters and experimental conditions employed in CZE and in RP-HPLC on the separation performance of phenolic compounds, which are widely distributed in the plant kingdom, form an integral part of human diet, and have a remarkable position as active components in cosmetics, functional foods and food supplements. The influence of the composition of either the electrolyte solution (BGE) or the mobile phase on the selective separation of bioactive secondary metabolites in CZE and RP-HPLC, respectively, is discussed. Appropriate selection 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. Also discussed is the practical application of RP-HPLC to study the occurrence of secondary metabolites in selected edible plants as a function of their genetic differences and environmental grown conditions, as well as the determination of phenolic compounds in agro-food matrices during the transformation of raw ingredients into food and in the production of food supplements.