Quercetin is a pentahydroxyflavone having the five hydroxy groups placed at the 3-, 3'-, 4'-, 5- and 7-positions. It is one of the most abundant flavonoids in edible vegetables, fruit and wine. It has a role as an antibacterial agent, an antioxidant, a protein kinase inhibitor, an antineoplastic agent, an EC 1.10.99.2 [ribosyldihydronicotinamide dehydrogenase (quinone)] inhibitor, a plant metabolite, a phytoestrogen, a radical scavenger, a chelator, an Aurora kinase inhibitor and a geroprotector. It is a pentahydroxyflavone and a 7-hydroxyflavonol. It is a conjugate acid of a quercetin-7-olate.