Kinetic Comparisons of Anthocyanin Reactivities towards 2,2′-Azobis(2-amidinopropane) (AAPH) Radicals, Hydrogen Peroxide and tert-Buthylhydroperoxide by Capillary Zone Electrophoresis

Abstract

Twelve major anthocyanins identified in bilberry extracts were studied in vitro using capillary zone electrophoresis (CZE) for their reactions towards 2,2′-azobis(2-amidinopropane) (AAPH) radicals, hydrogen peroxides (H₂O₂) and tert-buthylhydroperoxides (t-BuOOH). Reactivity towards AAPH radicals was primarily determined by the aglycon structure, not by the type of sugar moiety. Delphinidins carrying three-hydroxyl groups on the B ring were most reactive followed by cyanidins, with two-hydroxyl groups. Further, methylation of the hydroxyl groups reduced reactivity towards AAPH radicals. However, reactivity of anthocyanins towards H₂O₂ was not significantly affected by aglycon structure or by the type of sugar moiety; there being no marked difference in reaction rates among the anthocyanins. Reactivity towards t-BuOOH was essentially the same as towards H₂O₂, although the reaction rate was several times smaller. Also, the reaction rate of anthocyanin towards peroxide was relatively high compared to that of (+)-catechin (approximately 30 times larger) measured as a reference antioxidant, whereas the reactivities of anthocyanins and (+)-catechin towards AAPH radicals were similar.