Assessment of the antioxidant potential of Scotch whiskeys by electron spin resonance spectroscopy: Relationship to hydroxyl-containing aromatic components

Electron spin resonance (ESR) spectroscopy has been used to assess the anti oxidant capacity of eight Scotch whiskeys by measuring the extent by which the original spirits, or pyridine solutions of their residues, reduced Frem y's radical or galvinoxyl radical. All whiskeys displayed antioxidant activ ity greater than that of a 0.2 mM solution of Trolox in the Fremy's assay a nd of a 0.1 mM solution of quercetin in the galvinoxyl assay. The relative antioxidant capacities determined according to the two assays were highly c orrelated and strongly related to the total phenol content as determined by using the Folin-Ciocalteu method. Activity was a consequence of maturation in oak casks with the "newmake" spirit showing no effect. Of 10 aromatic c onstituents analyzed, activity was most strongly correlated with ellagic ac id and gallic acid in both assays. The reductive capacities of four major p henolics were determined, which, in summation, accounted for 31-53% of the total antioxidant activity of the whiskeys. There was no evidence for syner gistic interaction between the phenols investigated.