Extending Applicability of the Oxygen Radical Absorbance Capacity (ORAC−Fluorescein) Assay

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Abstract
The ORAC-fluorescein (ORAC−FL) method recently validated using automatic liquid handling systems has now been adapted to manual handling and using a conventional fluorescence microplate reader. As calculated for Trolox, the precision of the method was <3.0, expressed as percent coefficient of variation. The accuracy of the method was <2.3, expressed as percent variation of the mean. The detection and quantification limits were those corresponding to 0.5- and 1-μM Trolox standard solutions, respectively. The method has been applied to 10 pure compounds (benzoic and cinnamic acids and aldehydes, flavonoids, and butylated hydroxyanisole), to 30 white, rose, and bottled- and oak-aged red wines, and to 7 commercial dietary antioxidant supplements. All samples exhibited a good linear response with concentration. As seen by other methodologies, the chemical structure of a compound determines its antioxidant activity (ORAC−FL value). Of particular interest were the results with oak-aged red wines from different vintages (1989−2002) that confirm influence of vintage, but not origin of the oak, in the antioxidant activity of wines from the same variety. Dietary antioxidant supplements presented a great variability (170-fold difference) in their antioxidant potency. This work proves applicability of the ORAC−FL assay in evaluating the antioxidant activity of diverse food samples. Keywords: Antioxidant activity; ORAC; fluorescein; phenolics; wine; dietary antioxidant supplements