Polyphenol
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[[ca:Polifenol]]
{{Mergefrom|Polyphenol antioxidant|date=December 2007}}
'''Polyphenols''' are a group of chemical substances found in plants, characterized by the presence of more than one [[phenol]] unit or building block per molecule. Polyphenols are generally divided into hydrolyzable [[tannins]] ([[gallic acid]] esters of [[glucose]] and other sugars) and [[phenylpropanoid]]s, such as [[lignin]]s, [[flavonoid]]s, and condensed tannins.
== Chemistry ==
=== Classification and Nomenclature ===
The division of polyphenols into tannins, lignins, and flavonoids is derived from the variety of simple polyphenolic units derived from secondary plant metabolism of the [[shikimate]] pathway<ref>P. M. Dewick, ''The Biosynthesis of Shikimate Metabolites'', Natural Product Reports 12:579-607 (1995)</ref> as well as classical divisions based upon the relative importance of each base component to different fields of study. Tannin chemistry originated in the importance of [[tannic acid]] to the [[tanning|tanning industry]]; lignins to the chemistry of [[soil]] and plant structure; and flavonoids to the chemistry of plant secondary metabolites for [[Plant defense against herbivory|plant defense]], and flower color (e.g. from [[anthocyanins]]).
The largest and best studied polyphenols are the [[flavonoids]], which include several thousand compounds, among them the [[flavonols]], [[flavones]], [[catechins]], [[flavanones]], [[anthocyanidins]], and [[isoflavonoids]].<ref>''Clinical Guide to Nutrition and Dietary Supplements in Disease Management'', by Jennifer R. Jamison, ISBN 0-443-07193-4, page 525.</ref>
The most abundant polyphenols are the condensed tannins, found in virtually all families of plants, and comprising up to 50% of the dry weight of leaves. The convergent evolution of tannin-rich plant communities has occurred on nutrient-poor acidic soils throughout the world. Tannins were once believed to function as anti-herbivore defenses, but more and more ecologists now recognize them as important controllers of decomposition and nitrogen cycling processes. As concern grows about global warming, there is great interest to better understand the role of polyphenols as regulators of carbon cycling, particularly in northern boreal forests.
{| class="wikitable"
|-
!Base Unit:
| <center>[[Image:Gallic acid.svg|150px]]<center/><BR><center>[[Gallic Acid]]</center>
| <center>[[Image:2-Phenyl-1,4-benzopyrone.svg|173px]]</center><BR><center>[[Flavone]]</center>
| <center>[[Image:Cinnamic acid.svg|173px]]</center><BR><center>[[Cinnamic acid]]</center>
|-
!Class/Polymer:
| [[Tannin|hydrolyzable tannins]]
| [[Flavonoid]], [[tannin|condensed tannins]]
| <center>[[Lignin]]s</center>
|}
Polyphenols are also classified by the type and number of phenolic subcomponents present. More than one subcomponent can be present on a given polyphenol.
{| class="wikitable"
|-
| <center>[[Image:Phenol.svg|75px|Phenol]]</center>
| <center>[[Image:Pyrocatechol.svg|120px|Pyrocatechol]]</center>
| <center>[[Image:pyrogallol.svg|150px|Pyrogallol]]</center>
| <center>[[Image:Resorcine.svg|150px|Resorcinol]]</center>
| <center>[[Image:Phloroglucinol.svg|150px|phloroglucinol]]</center>
| <center>[[Image:Hydroquinone.svg|160px|Hydroquinone]]</center>
|-
| <center>[[Phenol]]</center>
| <center>[[Pyrocatechol]]</center>
| <center>[[Pyrogallol]]</center>
| <center>[[Resorcinol]]</center>
| <center>[[Phloroglucinol]]</center>
| <center>[[Hydroquinone]]</center>
|-
| Examples: [[coumaric acid]] derived lignins, [[kaempferol]]
| Examples: [[catechin]], [[quercetin]], [[caffeic acid|caffeic]] and [[ferulic acid]] derived lignins, [[hydroxytyrosol]] esters
| Examples: gallocatechins ([[EGCG]]), [[tannins]], [[myricetin]], [[sinapyl alcohol]] derived lignins
| Examples: [[resveratrol]]
| Examples: almost all [[flavonoid]]s
| Examples: [[arbutin]]
|}
The phenolic unit can often be [[esterification|esterified]] or [[methylation|methylated]]. It can also be found dimerized or further polymerized, creating a new class of polyphenol. For example, [[ellagic acid]] is a dimer of gallic acid and forms the class of ellagitannins, or a [[catechin]] and a gallocatechin can combine to form the red compound [[theaflavin]], a process which also results in the large class of brown [[thearubigin]]s in tea.
== In Foods ==
Notable sources of polyphenols include [[berries]], [[tea]], [[beer]], [[grapes]]/[[wine]], [[olive oil]], [[chocolate]]/[[cocoa]], [[walnuts]], [[peanut]]s, [[pomegranates]], [[yerba mate]], and other [[fruit]]s and [[vegetable]]s.
High levels of polyphenols can generally be found in the fruit skins.
== Health benefits ==
{{main|Polyphenol antioxidant}}
Polyphenols were once briefly known as Vitamin P. However they were quickly found out to be non-essential and reclassified. The health benefits of specific polyphenols such as [[Quercetin | quercetin]] are well-established, and there are less well-established claims of health benefits from all types of polyphenols.
Research indicates that polyphenols may have [[antioxidant]] characteristics with potential health benefits. They may reduce the risk of cardiovascular disease and cancer.
<ref>
Arts, I.C. and P.C. Hollman, "Polyphenols and disease risk in epidemiologic studies." ''American Journal Clinical Nutrition'', 2005. '''81'''(1 Suppl): p. 317S-325S.
</ref>
Polyphenols have also been investigated as a source of additional health benefit in organic produce, but no conclusion was made.
<ref>[http://nutrition.ucdavis.edu/perspectives/MayJune05.htm Nutrition Perspectives] Vol 30, No. 3 May/June 2005
</ref>
Polyphenols bind with nonheme iron (e.g. from plant sources) ''in vitro'' in model systems.
<ref>
E. Matuschek, U. Svanberg (2002) "[http://www.blackwell-synergy.com/doi/abs/10.1111/j.1365-2621.2002.tb11421.x?journalCode=jfds Oxidation of Polyphenols and the Effect on In vitro Iron Accessibility in a Model Food System]", ''Journal of Food Science'' '''67''' (1), pp. 420–424.
</ref>
This may decrease its absorption by the body.
== See also ==
* [[List of phytochemicals and foods in which they are prominent]]
* [[List of antioxidants in food]]
* [[Tannin]]
* [[Catechin]]
* [[Benzenediol]]
== References ==
<references />
== External links ==
* [http://www.frenchscout.com/types-of-red-wines Wine polyphenols vary with age and variety]
[[Category:Phenols]]
[[Category:Phytochemicals]]
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