Inactivation of quercetin mutagenicity.

Combinations of oxygen and alkaline pH were found to inactivate irreversibly the mutagenicity of quercetin towards Salmonella typhimurium strain TA98. Exposure time, quercetin concentration and polyphenol oxidase were also important variables determining the extent of quercetin inactivation. Temperature had a relatively weak influence on the extent of inactivation. The metal salts, ferrous, ferric and copper sulphates also brought about inactivation but this effect was partially reversed when the pH of the incubation medium was reduced from 7 to 2. Ferric sulphate had a much smaller effect than did the ferrous salt except in the presence of tyrosinase and oxygen at pH 7. Zinc sulphate impaired quercetin mutagenicity only very slightly in the presence of tyrosinase and oxygen. When an oxygen-saturated solution of quercetin was exposed to tyrosinase at various pH values, the ultraviolet absorption maximum of quercetin near 370 nm decreased to an extent that correlated with the mutagenicity of quercetin under those conditions.