Classification of Flavonoids, Health Benefits of Flavonoids

Fruits and vegetables are high on the list of recommended foods in the Dietary Guidelines for Americans. Scientists are keenly interested in learning which substances make fruits and vegetables so healthful. During the last decade, their curiosity has introduced us to a whole new language of phytonutrients, the beneficial compounds in plant foods.

The flavonoids are a group of plant pigments that exert antioxidant acitivity that is generally more potent and effective than traditional antioxidant nutrients vitamin C and E, beta-carotene, selenium, and zinc.

Health Benefits Flavonoids, particularly flavan-3-ols and proanthocyanidins, have been associated with reduction in the risk of cardiovascular disease by increasing the release of endothelial nitric oxide (NO) and preventing narrowing of the blood vessels. Anthocyanidins may also protect LDL cholesterol oxidation through their high antioxidant activity. Proanthocyanidins (PAs), the polymers of flavan-3-ols, also referred to as "Condensed Tannins", are known for contributing astringent flavor to foods. Recently it has been suggested that the free radical scavenging properties of PAs may reduce the risk of cancer, blood clotting and certain types of trimeric PAs may protect against urinary tract infections.

Flavonoids are also able to chelate (bind) metals, stimulate the immune system and also reduce an allergic response, impede cancer cell growth, and protect against bacteria and viruses.

Flavonoids ar sometimes called "nature's biological response modifiers" because of their anti-inflammatory, antiallergenic, antiviral, and their anticancer properties.

Foods contain more than 50 flavonoids, and they fit into several subclasses:

MAJOR FLAVONOID CLASSES Seven classes of flavonoids common in foods are usually considered for their medicinal properties:

1. Anthocyanidins
2. Proanthocyanidins
3. Flavones
4. Flavonols
5. Flavan-3-ols
6. Flavanones
7. Isoflavones

Compounds	Properties	Food Sources
Anthocyanidins
pelargonidin, cyanidin, delphinidin, peonidin, petunidin, malvidin, apigeninidin, luteolinidin, tricetinidin, aurantinidin, 6-hydroxy-cyanidin, 6-hydroxy-delphinidin, rosinidin, hirsutidin, 5-methyl-cyanidin, pulchellidin, europinidin, capensinidin	Anthocyanidins increase vitamin C levels within cells, decrease the breakage of small blood vessels, protect against free-radical damage, and help prevent destruction of collagen thus promoting healthy skin and connective tissue.	The anthocyanidins are most abundant in fruits and red wine and less frequent in vegetables. Best food sources: blueberries, blackberries, plums, cranberries, raspberries, red onions, red potatoes, red radishes, and strawberries.
Proanthocyanidins
monomers, dimers, trimers, 4-6 mers (tetramers, pentamers and hexamers), 7-10 mers (heptamers, octamers, nonamers and decamers), polymers (DP>10)	This group of polymers, if broken apart with acid treatment, yield anthocyanidins such as cyanidin. Proanthocyanidins are sometimes referred to as "condensed tannins" and are responsible for astringency in many foods and medicinal herbs. Proanthocyanidins have strong antioxidant properties and may reduce the risk of cardiovascular disease and cancer. Some proanthocyanidins may protect against urinary tract infections.	Best sources: tea, cocoa, many berries, grapes/grape juice, cranberries/cranberry juice, and red wine.
Flavones
apigenin, luteolin, tangeretin, nobiletin	Apigenin has chemopreventive properties. Luteolin has been shown in animal studies to have anti-cancer, anti-inflammatory, anti-allergic effects, and anti-asthma effects. Tangeretin and nobiletin, citrus polymethoxylated flavones found in the peel of citrus fruits exhibit anti-proliferative, anti-invasive, anti-metastatic, and antioxidant activities. They also have the potential to reduce blood pressure and plasma glucose levels.	Apigenin: celery, lettuce, parsley Luteolin: beets, bell peppers, Brussels sprouts, cabbage, cauliflower, celery, hot peppers, lettuces, spinach, thyme Tangeretin & nobiletin: peel of citrus fruits; shekwasha (citrus fruit)
Flavonols
myricetin, quercetin, isorhamnetin, kaempferol, isorhamnetin	Myricetin has anti-inflammatory and anti-cancer effects. Quercetin, the main flavonoid in the diet, may lower risk for asthma, heart disease, and lung cancer.	Best sources for myricetin: berries, grapes, parsley, spinach. Best sources for quercetin: onions, apples, broccoli, cranberries, grapes
Flavan-3-ols
catechins and gallic acid esters of catechins, epicatechins and gallic acid esters of epicatechins, theaflavins and gallic acid esters of theaflavins, thearubigins	Catechins and epicatechins may lower the risk of coronary heart disease, some types of cancers and promote healthy lungs (catechins).	Best sources for catechins: tea, red wine, cocoa powder, dark chocolate, grapes, plums Best sources for epicatechins: teas, fruits and legumes (beans)
Flavanones
hesperetin, naringenin, eriodictyol	Hesperetin found in grapefruits and oranges is one candidate that may benefit the cardiovascular system (atherothrombotic diseases PubMed), and lower the levels of LDL cholesterol. Naringenin has antioxidant, anti-estrogen, and cholesterol-lowering properties.	Best sources for hesperetin: citrus fruits and juices Best sources for naringenin: citrus fruits and juices
Isoflavonoids
daidzein, genistein	Isoflavonoids (also called isoflavones) have been suggested to have strong antioxidative properties.	Best sources: soya, soya products,red clover

Western diets provide from several milligrams to a gram of flavonoids each day. Mixed diets contain flavonoids from all five subclasses. Most of the food flavonoids have glucose or some other sugar attached. These sugar-coated flavonoids are called falvonoid glycosides.

Flavonoid Retention in Berries, Fruits and Vegetables  Fruit and berry juices prepared using common commercial methods offer little anti-cancer and other health benefits from flavonoids.