An assessment of the anti-oxidant and pro-oxidant profiles of red wine and selected phenolic components

INTRODUCTION: Red wine contains a rich matrix of phenolic compounds which have been found to possess anti-oxidant properties. These phenolic anti-oxidants have considerable potential in preventing inflammation and oxidative stress. However, many of these dietary components can also exhibit pro-oxidant activity under certain experimental conditions, such as in the presence of redox-active transition metal ions. A great deal of research has focussed on the anti-oxidant potential of red wine. However, studies on the potential pro-oxidant effects are limited. AIMS: This research aimed to contribute to existing knowledge by delineating both the anti-oxidant and pro-oxidant profiles of red wine and selected individual phenolic compounds in the presence of various oxidant systems. METHODS: A new functional-based TLC approach was used to screen the anti¬oxidant profile of red wine in the presence of hydrogen peroxide, Fe3+ and Cu2+ metal ions. A quantitative approach using a reversed-phase HPLC method was developed to further assess the relative anti-oxidant activities of wine and its phenolic compounds. Pro-oxidant effects of wine were investigated using the hydroxyl radical-mediated deoxyribose degradation assay and inhibition of linoleic acid peroxidation assay. The effect of Fe3+ and Cu2+ on the anti-oxidant activities of other grape-based products was also carried out using modified forms of the ABTS'+ and DPPH assays. RESULTS.: Functional TLC revealed that quercetin and caffeic acid were found to be the most potent anti-oxidants, with overall ranking of the five anti-oxidants in the order: quercetin> caffeic acid> gallic acid> p-coumaric acid> chlorogenic acid. RP-HPLC showed similar results, with quercetin and. caffeic acid exhibiting the highest anti-oxidant efficacies. Gallic acid and p-coumaric acid, however, showed lower activities. The Fenton systems were shown to have a greater oxidising power relative to the oxidants added alone. In the hydroxyl radical-mediated deoxyribose degradation assay, red wine exhibited decreased anti-oxidant potential as the concentration increased, and was pro-oxidant at 640 mgIL. However, it was an efficient inhibitor of linoleic acid peroxidation, with inhibition ranging from 73.93-82.59 %. All phenolic standards showed pro-oxidant activities, with gallic add the highest (-62.12 %), and kaempferol the lowest (-19.70 %). The modified DPPH and ABTS•+ assays revealed a reduction in anti-oxidant capacity for wines and grape juices in the presence of metal ions, with Cu2+ showing a greater reduction in activity than Fe3+ in the ABTS•+ assay. For red wine, anti-oxidant activity ranged from 4556.72-4782.09 mg TElL in the presence of Fe3+, whereas this decreased to between 3444.78 and 3600.00 mg TElL when Cu2+ was added. CONCLUSIONS: The study demonstrated the first application of functional TLC and HPLC to delineate the anti-oxidant profile of red wine in the presence of different oxidant systems involving H202 and redox-active metal ions. The results suggested that red wine and its phenolic compounds can exhibit pro-oxidant potential under certain experimental conditions. The reduced anti-oxidant capacity of other grape-based products in the presence of metal ions also suggested potential pro-oxidant effects. Overall, a more detailed examination of metal ion-phenolic anti-oxidant interactions must be fully explored in order to determine potential pro-oxidant effects in biological systems