Chelating Properties and Hydroxyl-Scavenging Activities of Hop α- and Iso-α-Acids

Metal chelation and scavenging of highly reactive hydroxyl radicals are commonly proposed to explain the antioxidant behavior of hop acids. In the current study, an assay measuring the oxidative degradation of 2-deoxyribose (2-DR) by hydroxyl radicals was used to elucidate these mechanisms and examine the origin of the ability of hop acids to prevent oxidative damage. Hop α- and iso-α-acids were able to prevent 2-DR oxidative degradation; however, α-acids appeared to be 60% more effective than iso-α-acids. The ability of hop acids to inhibit 2-DR oxidative degradation could be inversely correlated with Fe2+ concentration, which suggests that they prevent 2-DR oxidation by chelating iron. Moreover, it was demonstrated that these hop acids were not capable of scavenging hydroxyl radicals. Further trials showed that hop α- and iso-α-acids enhanced Fe2+ autoxidation to Fe3+ when complexing it and, thus, lowered the catalytic function of the iron in the Fenton reaction system.