Background: 

flavonols are phenol derivatives present in substantial amounts in fruit, vegetables and few types of beverages such as tea and wine. They are antioxidant against free radicals and so they have a functional physiologic role. The mechanism of antioxidant activity of these molecules has not get described in any detail, especially the possible influence of pH on the antioxidant properties.

Aim: 

the purpose of this study was to evaluate the antioxidant or pro-oxidant behaviours of some typical flavonols of red wine, to investigate the influence of pH to the antioxidant properties and to elucidate their

activity-structure relationships.

Methods: 

Antioxidant activity (AA) of compounds in hydrophilic solutions at different pH was measured by a competition kinetics test, based on the crocin bleaching.

Results: 

data obtained show significant pH-dependent influence on the AA of phenolic compounds and also reveal a change in the mechanism of antioxidant action upon hydroxyl moiety deprotonation. In fact quercetin, for example, evidence a considerable reduction in AA at pH 3,5 compared to the AA measured at pH 7,4 and pH 9. AA of quercetin

varied from 0,00046±0,12 to 0,01±0,004 proportionally to increase of pH.

Conclusions: 

It is important take into account that these compounds could have a different ability to trap the free radicals in relationship to their different natural sources and they could undergo

a change in the antioxidant action when they are absorbed in to the human intestine.