Flavonoid

Biosynthesis

Flavonoids are synthesized by the proanthocyanidins (tannins) and a host of other polyphenolics.

Biological effects

Flavonoids are widely distributed in plants fulfilling many functions including producing yellow or red/blue anti-inflammatory^[4] , anti-microbial and anti-cancer activity.

Consumers and food manufacturers have become interested in flavonoids for their medicinal properties, especially their potential role in the prevention of cancers and cardiovascular disease. The beneficial effects of fruit, vegetables, and tea or even red wine have been attributed to flavonoid compounds rather than to known vitamins.

Health Benefits Aside From Antioxidant Values

In 2007, research conducted at the Linus Pauling Institute and published in Free Radical Biology and Medicine indicates that inside the human body, flavonoids themselves are of little or no direct antioxidant value. Unlike in the controlled conditions of a test tube, flavonoids are poorly absorbed by the human body (less than 5%), and most of what is absorbed is quickly metabolized and excreted from the body.

The huge increase in antioxidant capacity of blood seen after the consumption of flavonoid-rich foods is not caused directly by the flavonoids themselves, but most likely is due to increased uric acid levels that result from expelling flavonoids from the body.^[2] According to Frei, "we can now follow the activity of flavonoids in the body, and one thing that is clear is that the body sees them as foreign compounds and is trying to get rid of them. But this process of gearing up to get rid of unwanted compounds is inducing so-called Phase II enzymes that also help eliminate mutagens and carcinogens, and therefore may be of value in cancer prevention... Flavonoids could also induce mechanisms that help kill cancer cells and inhibit tumor invasion."^[2]

Their research also indicated that only small amounts of flavonoids are necessary to see these medical benefits. Taking large dietary supplements provides no extra benefit and may pose some risks.^[2]

Diarrhea

A study done at Children's Hospital & Research Center Oakland, in collaboration with scientists at Heinrich Heine University in Germany, has shown that epicatechin, cystic fibrosis transmembrane conductance regulator Cl– transport inhibiting cAMP-stimulated Cl– secretion in the intestine.^[5]

Important flavonoids

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Quercetin

vitamin C-sparing action. It has been found to be anti-cancer. Quercetin can be found in the herbal products based on Hawthorn, which are used for acute symptoms of Congestive Heart Failure.

Epicatechin

Epicatechin improves blood flow and thus seems good for cardiac health. green tea in in-vitro tests.^{[6] [7]} But in the test outlined above it now appears the beneficial antioxidant effects are minimal as the antioxidants are rapidly excreted from the body.

Oligomeric proanthocyanidins

Proanthocyanidins extracts demonstrate a wide range of pharmacological activity. Their effects include increasing intracellular collagen, the most abundant protein in the body.

Important dietary sources

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Good sources of flavonoids include all citrus fruits, berries, onions, cocoa content of seventy percent or greater).

Citrus

The citrus bioflavonoids include reverse transcriptase, part of the replication process of retroviruses.^[8] The therapeutical relevance of this inhibition has not been established. Hydroxyethylrutosides (HER) have been used in the treatment of capillary permeability, easy bruising, hemorrhoids, and varicose veins.

Tea

catechins (catechin, epicatechin, epicatechin gallate, and epigallocatechin gallate (EGCG)).

In producing teas such as oolong tea and black tea, the leaves are allowed to leaf, which inactivates these enzymes, and oxidation does not significantly occur.

Wine

Grape skins contain significant amounts of flavonoids as well as other polyphenols^[9]. Both red and white wine contain flavonoids; however, since red wine is produced by fermentation in the presence of the grape skins, red wine has been observed to contain higher levels of flavonoids, and other polyphenolics such as resveratrol.

Subgroups

Over 5000 naturally occurring flavonoids have been characterized from various plants. They have been classified according to their chemical structure, and are usually subdivided into the following subgroups (for further reading see ^[3]):

Flavones

Flavones are divided into four groups:^[10]

• Flavones

  Flavones use the 2-phenylchromen-4-one skeleton.

  Examples: Tangeritin

• Flavonols

  Flavonols or 3-hydroxyflavones use the 3-hydroxy-2-phenylchromen-4-one skeleton.

  Examples: Myricetin, Fisetin, Isorhamnetin, Pachypodol, Rhamnazin

• Flavanones

  Flavanones use the 2,3-dihydro-2-phenylchromen-4-one skeleton.

  Examples: Hesperetin, Naringenin, Eriodictyol, Homoeriodictyol.

• 3-Hydroxyflavanones or 2,3-dihydroflavonols

  3-Hydroxyflavanones use the 3-hydroxy-2,3-dihydro-2-phenylchromen-4-one skeleton.

  Examples: Dihydroquercetin, Dihydrokaempferol

Isoflavones

• Isoflavones

  Isoflavones use the 3-phenylchromen-4-one skeleton.

  Examples: Genistein, Daidzein, Glycitein

Flavan-3-ols and Anthocyanidins

• Flavan-3-ols

  Flavan-3-ols use the 2-phenyl-3,4-dihydro-2H-chromen-3-ol skeleton.

  Examples: Catechins (Epicatechins (Epicatechin (EC), Epigallocatechin (EGC), Epicatechin 3-gallate (ECg), Epigallocatechin 3-gallate (EGCg))

• Anthocyanidins

  Anthocyanidins are the flavylium (2-phenylchromenylium) ion skeleton

  Examples: Peonidin, Petunidin

Availability through microorganisms

A number of recent research articles have demonstrated the efficient production of flavonoid molecules from genetically-engineered microorganisms^[11][12].

See also

• Phytochemistry

References

v • d • e Types of Furanocoumarin • Lignans • Lignins • Suberins

Flavonoids:
Flavones:	Flavoxate
Isoflavones:	Genistein | Daidzein | Biochanin A | Formononetin | Coumestrol | Daidzin | Puerarin
Flavonols:	Kaempferol | Fisetin | Isorhamnetin | Pachypodol | Rhamnazin
Flavanones:	Hesperetin | Naringenin | Eriodictyol | Homoeriodictyol
3-Hydroxyflavanones:	Dihydroquercetin | Dihydrokaempferol
Flavan-3-ols:	Catechins | Epicatechins | Epigallocatechin
Anthocyanidins:	Peonidin | Petunidin
Misc:	List of phytochemicals and foods in which they are prominent