Evaluation of the Antioxidant Abilities of Water-Soluble Biosubstances Using the ORAC-ESR Assay in Combination with the Hydroxyl and Superoxide Radical-Eliminating Abilities

Abstract

The oxygen radical absorbance capacity (ORAC) values of various water-soluble biosubstances using the ORAC-electron spin resonance (ESR) assay were examined, and an advanced database of water-soluble biosubstances in combination with the hydroxyl and the superoxide radical-eliminating abilities was prepared. The ORAC-ESR assay is based on the competitive reaction between the spin trapping of the 2,2′-azobis(2-amidinopropane) dihydrochloride (AAPH)-derived alkoxyl radical and its elimination by substrate. The alkoxyl radical-eliminating ability of substrate was calculated from the decrease in the ESR signal of the 5-(2,2-dimethyl-1,3-propoxy cyclophosphoryl)-5-methyl-1-pyrroline N-oxide (CYPMPO) spin adduct of the alkoxyl radical. The determination of ORAC values was performed by determining the specificity of a spin trap relative to a standard radical eliminator, 6-hydroxy-2,5,7,8-tetramethylchroman-2-carboxylic acid (Trolox). The ORAC values [μmol Trolox equivalent (TE)/g] of water-soluble biosubstances were classified into three groups, the high value group (over 10,000 μmol TE/g), the intermediate value group (400–10,000 μmol TE/g), and the low value group (<100 μmol TE/g). The two-dimensional diagrams for the ORAC values (μmol TE/g) and the hydroxyl and superoxide radical-eliminating abilities (1/[\( {\text{id}}^{\text{h}}_{ 5 0} \)(mg/ml)] and 1/[\( {\text{id}}^{\text{s}}_{50} \)(mg/ml)], respectively) were depicted. Biosubstances having higher ORAC values had higher superoxide radical-eliminating abilities (the correlation factor 0.73). Little correlation between the ORAC values and the 1/[\( {\text{id}}^{\text{h}}_{ 5 0} \)(mg/ml)] values (the correlation factor 0.32) was observed. The obtained diagrams should provide a database for the study of the antioxidant abilities of foods and pharmaceutics.