Catechin, epicatechin, quercetin, rutin and resveratrol in red grape: Content, in vitro antioxidant activity and interactions

The extracts obtained from skin and seeds of 10 native Tuscan and international Vitis vinifera varieties were evaluated for their antioxidant activity, total phenolic and anthocyanin content and subjected to HPLC–UV analysis to quantify the content of five phenolic constituents of biological interest: catechin and epicatechin in seeds and quercetin, rutin and resveratrol in skin extracts. The antioxidant activity of the extracts and pure compounds was assessed by means of two different in vitro tests: scavenging of the stable DPPH radical and of authentic peroxynitrite (ONOO−). All the extracts showed significant antiradical capacity: Merlot skin was most active towards both radicals. All the five phenols investigated possessed strong antiradical activity. Quercetin, catechin and epicatechin showed maximum activity (respectively, IC50(DPPH)IC50(DPPH) 5.5, 6.7 and 6.8 μM, IC50(ONOO-)IC50(ONOO-) 48.8, 55.7 and 56.7 μM). Potential antiradical interactive effects among the five compounds were also investigated and results indicated possible synergy between quercetin, rutin and resveratrol towards ONOO−. The effect was additive for catechin and epicatechin.