Flavonoid antioxidants

Flavonoids (or bioflavonoids; from the Latin word flavus, meaning yellow, their color in nature) are a class of polyphenolic secondary metabolites found in plants. Blackberry, black currant, chokeberry, and red cabbage are examples of plants with rich contents of flavonoids. In plant biology, flavonoids fulfill diverse functions, including attraction of pollinating insects, antioxidant protection against ultraviolet light, deterrence of environmental stresses and pathogens, and regulation of cell growth.

thumb|right|class=skin-invert-image|UV visible spectrum of quercetin, with lambda max at 369 nm

Rutin (rutoside, quercetin-3-O-rutinoside or sophorin) is the glycoside combining the flavonol quercetin and the disaccharide rutinose (α-L-rhamnopyranosyl-(1→6)-β-D-glucopyranose). It is a flavonoid glycoside found in a wide variety of plants, including citrus.

Genistein (C15H10O5) is a plant-derived, aglycone isoflavone. Genistein has the highest content of all isoflavones in soybeans and soy products, such as tempeh. As a type of phytoestrogen, genistein is classed as an endocrine disrupting chemical due to its estrogenic activity in vitro and in vivo. Consequently, excessive consumption of soy products has been linked to disruption of the reproductive organs, such as the uterus, breast, and testis.

Hesperidin is a flavanone glycoside found in citrus fruits. Its aglycone is hesperetin. Its name is derived from the word "hesperidium", for fruit produced by citrus trees.

Kaempferol (3,4′,5,7-tetrahydroxyflavone) is a natural flavonol, a type of flavonoid, found in a variety of plants and plant-derived foods, including kale, beans, tea, spinach, and broccoli. It is also found in propolis extracts. Kaempferol is a yellow crystalline solid with a melting point of . It is slightly soluble in water and highly soluble in hot ethanol, ethers, and DMSO. Kaempferol is named for 17th-century German naturalist Engelbert Kaempfer.

Pinocembrin is a flavanone, a type of flavonoid. It is an antioxidant found in damiana, honey, fingerroot, and propolis.

Proanthocyanidins are a class of polyphenols found in many plants, such as cranberry, blueberry, and grape seeds. Chemically, they are oligomeric flavonoids. Many are oligomers of catechin and epicatechin and their gallic acid esters. More complex polyphenols, having the same polymeric building block, form the group of condensed tannins.

Pinobanksin is an antioxidant bioflavonoid (specifically a flavanonol, a category of flavonol) that inhibits peroxidation of low density lipoprotein and it has electron donor properties reducing alpha-tocopherol radicals. It is present in sunflower honey.

Barbigerone is one of a few pyranoisoflavones among several groups of isoflavones. It was first isolated from the seed of a leguminous plant Tephrosia barbigera; hence the name "barbigerone". Members of the genus Millettia are now known to be rich in barbigerone, including M. dielsiena, M. ferruginea, M. usaramensis, and M. pachycarpa. It has also been isolated from the medicinal plant Sarcolobus globosus. Barbigerone from S. globosus is validated to have significant antioxidant property. Barbigerone exhibits profound antiplasmodial activity against the malarial parasite Plasmodium falciparum.

thumb|Epicatechin (EC), one of the building blocks of procyanidins thumb|Cyanidin, the anthocyanidin produced when procyanidin are depolymerized under oxidative conditions Procyanidins are members of the proanthocyanidin (or condensed tannins) class of flavonoids. They are oligomeric compounds, formed from catechin and epicatechin molecules. They yield cyanidin when depolymerized under oxidative conditions.