Total Oxygen Radical Absorbance Capacity Research Articles

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-scavenging 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.

A Device for the Semiautomatic Determination of Oxygen-Radical Absorbance Capacity

The oxygen-radical absorbance capacity (ORAC) assay has become a standard method to quantify the antioxidative properties of phytonutrients in fruit and vegetable extracts. However, it is usually not possible to determine directly the contribution of specific phytonutrients to the total ORAC value. Separation of the components in the plant extracts by HPLC followed by ORAC analyses of the column fractions might permit the determination of free radical-scavenging profiles. The accurate determination of ORAC values may require 1 to 2 h/sample. Considering the number of samples that would be generated by a single HPLC separation, a device was constructed which permits up to 45 simultaneous ORAC analyses. Varying degrees of automation were included in the design. Furthermore, since the assay has a Q10 for peroxyl radical-scavenging of about 3, elevation of the assay temperature from the standard 37 to 47°C significantly reduced the assay times. Relatively simple modifications would allow the apparatus to be used in a variety of time-dependent fluorescence and absorbance assays.

Total Antioxidant Capacity of Fruits

The total antioxidant activity of 12 fruits and 5 commercial fruit juices was measured in this study using automated oxygen radical absorbance capacity (ORAC) assay. On the basis of the wet weight of the fruits (edible portion), strawberry had the highest ORAC activity (micromoles of Trolox equivalents per gram) followed by plum, orange, red grape, kiwi fruit, pink grapefruit, white grape, banana, apple, tomato, pear, and honeydew melon. On the basis of the dry weight of the fruits, strawberry again had the highest ORAC activity followed by plum, orange, pink grapefruit, tomato, kiwi fruit, red grape, white grape, apple, honeydew melon, pear, and banana. Most of the antioxidant capacity of these fruits was from the juice fractions. The contribution of the fruit pulp fraction (extracted with acetone) to the total ORAC activity of a fruit was usually less than 10%. Among the commercial fruit juices, grape juice had the highest ORAC activity followed by grapefruit juice, tomato juice, orange juice, and apple juice. Keywords: Free radicals; antioxidant; peroxyl radical; fruits