Plant polyphenols are appreciated as dietary supplements and functional food ingredients. Their putative health promoting action may originate, at least in part, from their influence on the delicate redox balance governing cell functions. In vivo, flavonoids, particularly catechins, may be antioxidants or prooxidants depending on their structure and concentration. The accurate evaluation of the redox behavior of flavonoids should help defining their beneficial or toxic effects. Proanthocyanidin (oligomeric catechin) fractions and bio-based products from grape, pine and witch hazel with variable proportions of catechol and pyrogallol (two and three adjacent enolic hydroxyl groups respectively) moieties were prepared and tested on stable free radicals and for in vitro activity on skin and colon cells to show that there may be a relationship between the electron transfer capacity of proanthocyanidins and their influence on cell functions such as proliferation and apoptosis

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