Oxygen radical absorbance capacity of the phenolic compounds in plant extracts fractionated by high-performance liquid chromatography

The oxygen radical absorbance capacity (ORAC) assay has been used to quantify the antioxidative properties of phytonutrients in fruit and vegetable extracts. Using aqueous methanol extracts of tea and spinach as a model systems, separation of the components in the extracts by HPLC followed by semiautomatic ORAC analysis of the column fractions permitted the determination of peroxyl-radical-scavensnging profiles, demonstrating the relative abilities of the individual extract components to scavenge peroxyl radicals. ORAC values for up to 80 HPLC fractions were measured, confirming the major contribution of epigallocatechin gallate in the peroxyl radical scavenging of green tea extracts. Although the flavonoids in spinach extracts provided resistance to peroxyl radicals, components that did not bind to the HPLC column and simple phenolic compounds may also be important contributors to the total ORAC activity of spinach leaf extracts. Application of these procedures to plants believed to provide certain human health benefits by reducing free radicals may allow the identification and characterization of the specific components responsible for the free-radical-scavenging activities. (C) 2001 Academic Press.