Electron spin resonance spectroscopy studies on the free radical scavenging activity of wine anthocyanins and pyranoanthocyanins

Anthocyanins are a group of natural occurring pigments responsible for the red‐blue color of grapes and many fruits and vegetables. Anthocyanins and derived pigments are of double interest, one technological, as they can be used as natural colorants, and another one due to their implication on human health through their antioxidant activity. Although there are numerous studies regarding the antioxidant activity of grape extracts as well as red wine, the free radical scavenging activity of purified anthocyanins and pyranoanthocyanins is largely unknown. In the present study, the hydroxyl and superoxide anion scavenging activities of anthocyanins and their pyruvic acid adducts were systematically investigated by electron spin resonance spectroscopy and spin trapping. The 3‐glucosides of delphinidin, cyanidin, petunidin, pelargonidin and malvidin, and the pyruvic adduct of the 3‐glucoside of delphinidin exhibited a potent superoxide anion radical scavenging and, to a lesser extent hydroxyl anion radical scavenging activity. The pyranoanthocyanins of cyanidin, petunidin, malvidin and pelargonidin showed a high capacity to scavenge superoxide anion radicals but did not scavenge hydroxyl radicals. Current data indicate that formation of anthocyanin adducts with pyruvic acid, which may occur during wine ageing or fruit juice processing, decreases the hydroxyl and superoxide anion scavenging and thus could decrease the antioxidant potential of these compounds.