View source for Antioxidant effect of polyphenols and natural phenols

[[Image:Blackberry fruits10.jpg|thumb|200px|[[Blackberry|Blackberries]] are a source of polyphenols.]]
A '''polyphenol antioxidant''' is a [[hypothesis|hypothesized type]] of [[antioxidant]] studied [[in vitro]]. Numbering over 4,000 distinct [[chemical structures]] mostly from [[plant]]s, such polyphenols have not been demonstrated to be antioxidants [[in vivo]].<ref name="lpi"> {{cite web |title=Flavonoids|url=http://lpi.oregonstate.edu/mic/dietary-factors/phytochemicals/flavonoids|publisher=Micronutrient Information Center, Linus Pauling Institute, Oregon State University|location=Corvallis, OR|access-date=31 January 2018|date=November 2015}}</ref><ref name=Williams> {{cite journal |vauthors=Williams RJ, Spencer JP, Rice-Evans C |title=Flavonoids: antioxidants or signalling molecules? |journal=Free Radical Biology & Medicine |volume=36 |issue=7 |pages=838–49 |date=April 2004 |pmid=15019969 |doi=10.1016/j.freeradbiomed.2004.01.001}}</ref><ref name=Frei>{{Cite web|author=Frei B |title=Controversy: What are the true biological functions of superfruit antioxidants? |publisher=Natural Products Information Center |url=http://www.npicenter.com/anm/templates/newsATemp.aspx?articleid=23667&zoneid=273 |date=April 1, 2009 |url-status=dead |archive-url=https://web.archive.org/web/20100306080108/http://www.npicenter.com/anm/templates/newsATemp.aspx?articleid=23667&zoneid=273 |archive-date=March 6, 2010 }}</ref>
In vitro at high experimental doses, polyphenols may affect cell-to-cell signaling, [[receptor (biochemistry)|receptor]] sensitivity, inflammatory [[enzyme]] activity or [[gene regulation]].<ref name=Frei/><ref name=Virgili>{{cite journal |vauthors=Virgili F, Marino M |title=Regulation of cellular signals from nutritional molecules: a specific role for phytochemicals, beyond antioxidant activity |journal=Free Radical Biology & Medicine |volume=45 |issue=9 |pages=1205–16 |date=November 2008 |pmid=18762244 |doi=10.1016/j.freeradbiomed.2008.08.001}}</ref> None of these hypothetical effects has been confirmed in humans by high-quality [[clinical research]], {{asof|2020|lc=y}}.<ref name=lpi/>
==Sources of polyphenols==
The main source of polyphenols is dietary, since they are found in a wide array of [[phytochemical]]-bearing foods.  For example, [[honey]]; most [[legume]]s; fruits such as [[apple]]s, [[blackberry|blackberries]], [[blueberry|blueberries]],  [[cantaloupe]], [[pomegranate]], [[cherry|cherries]], [[cranberry|cranberries]], [[grape]]s, [[pear]]s, [[plum]]s, [[raspberry|raspberries]], [[aronia berry|aronia berries]], and [[strawberry|strawberries]] (berries in general have high polyphenol content<ref>{{Cite journal|last1=Hidalgo|first1=Gádor-Indra|last2=Almajano|first2=María Pilar|date=2017|title=Red Fruits: Extraction of Antioxidants, Phenolic Content, and Radical Scavenging Determination: A Review|journal=Antioxidants|language=en|volume=6|issue=1|pages=7|doi=10.3390/antiox6010007|pmid=28106822|pmc=5384171|doi-access=free}}</ref>) and [[vegetable]]s such as [[broccoli]], [[cabbage]], [[celery]], [[onion]] and [[parsley]] are rich in polyphenols. [[Red wine]], [[chocolate]], black tea, [[white tea]], [[green tea]], [[olive oil]] and many [[grain]]s are sources.<ref name=lpi/> Ingestion of polyphenols occurs by consuming a wide array of plant foods.<ref name=lpi/>
== Biochemical theory ==
The regulation theory considers a polyphenolic ability to scavenge [[free radical]]s  and up-regulate certain metal [[chelation]] reactions.<ref name=lpi/>  Various [[reactive oxygen species]], such as [[singlet oxygen]], [[peroxynitrite]] and  [[hydrogen peroxide]], must be continually removed from cells to maintain healthy metabolic function. Diminishing the concentrations of reactive oxygen species can have several benefits possibly associated with [[ion transport]] systems and so may affect [[redox signaling]].<ref name=lpi/> There is no substantial evidence, however, that dietary polyphenols have an antioxidant effect in vivo.<ref name=lpi/><ref name=gross/>
The “deactivation” of oxidant species by polyphenolic antioxidants (POH) is based, with regard to food systems that are deteriorated by peroxyl radicals (R•), on the donation of hydrogen, which interrupts chain reactions:
:R• + PhOH → R-H + PhO•
Phenoxyl radicals (PO•) generated according to this reaction may be stabilized through [[Resonance (chemistry)|resonance]] and/or intramolecular hydrogen bonding, as proposed for [[quercetin]], or combine to yield [[dimer (chemistry)|dimer]]isation products, thus terminating the chain reaction:
:PhO• + PhO•→ PhO-OPh <ref>{{Cite book| doi=10.1016/0076-6879(90)86128-I| pmid=2172711| chapter=&#91;36&#93; Flavonoids as antioxidants: Determination of radical-scavenging efficiencies| title=Oxygen Radicals in Biological Systems Part B: Oxygen Radicals and Antioxidants| volume=186| pages=[https://archive.org/details/oxygenradicalsin0000unse/page/343 343–55]| series=Methods in Enzymology| year=1990| last1=Bors| first1=Wolf| last2=Heller| first2=Werner| last3=Michel| first3=Christa| last4=Saran| first4=Manfred| isbn=978-0121820879| chapter-url=https://archive.org/details/oxygenradicalsin0000unse/page/343}}</ref>
==Potential biological consequences==
[[Image:Macrophage.jpg|thumb|right|250px|A [[macrophage]] stretching its arms to engulf two particles. Reactive oxygen species promote oxidized [[Low-density lipoprotein|LDL]].]]
Consuming dietary polyphenols have been evaluated for biological activity in vitro, but there is no evidence from high-quality [[clinical research]] {{asof|2015|lc=y}} that they have effects in vivo.<ref name=lpi/> Preliminary research has been conducted and regulatory status was reviewed in 2009 by the U.S. [[Food and Drug Administration]] (FDA), with no recommended intake values established, indicating absence of proof for nutritional value.<ref name="gross">{{citation |title= New Roles for Polyphenols. A 3-Part Report on Current Regulations and the State of Science |author=Gross, Paul |date=1 March 2009 |publisher= Nutraceuticals World |url= http://www.nutraceuticalsworld.com/issues/2009-03/view_features/new-roles-for-polyphenols/ }}</ref> Other possible effects may result from consumption of foods rich in polyphenols, but are not yet proved scientifically in humans; accordingly, health claims on food labels are not allowed by the FDA.<ref name=gross/>
== Difficulty in analyzing effects of specific chemicals ==
[[Image:Close up grapes.jpg|thumb|190px|left|[[Grape]]s contain certain polyphenol compounds, although none has been shown to be an antioxidant in vivo.]]
It is difficult to evaluate the physiological effects of specific natural phenolic antioxidants, since such a large number of individual compounds may occur even in a single food and their fate in vivo cannot be measured.<ref name=lpi/><ref name=gross/><ref>{{cite journal |last1=Carocho |first1=M |last2=Ferreira |first2=IC |title=A review on antioxidants, prooxidants and related controversy: natural and synthetic compounds, screening and analysis methodologies and future perspectives. |journal=Food and Chemical Toxicology |date=January 2013 |volume=51 |pages=15–25 |doi=10.1016/j.fct.2012.09.021 |pmid=23017782|hdl=10198/8534 |hdl-access=free }}</ref>
Other more detailed chemical research has elucidated the difficulty of isolating individual phenolics. Because significant variation in phenolic content occurs among various brands of tea, there are possible<ref>C. Fajardo-Lirai, S. M. Henning, H. W. Lee, V. L. W. Go, and D. Heber,. Department Family Environmental Sciences/Nutrition, Dietetics & Food Science, California State University, Northridge and, UCLA Center for Human Nutrition, Session 46C, 2002 Annual meeting of Food Expo, Anaheim, Ca</ref> inconsistencies among epidemiological studies implying beneficial health effects of phenolic antioxidants of [[green tea]] blends. The [[Oxygen Radical Absorbance Capacity]] (ORAC) test is a laboratory indicator of antioxidant potential in foods and [[dietary supplement]]s. However, ORAC results cannot be confirmed to be physiologically applicable and have been designated as unreliable.<ref name=Frei/><ref name=USDAx>{{cite web |url=http://www.ars.usda.gov/services/docs.htm?docid=15866 |title=Withdrawn: Oxygen Radical Absorbance Capacity (ORAC) of Selected Foods, Release 2 (2010)  |date=16 May 2012 |publisher=United States Department of Agriculture, Agricultural Research Service |access-date=31 January 2018}}</ref>
==Practical aspects of dietary polyphenols==
[[Image:Cacao-pod-k4636-14.jpg|thumb|[[Cocoa bean|Cocoa]] is the prime ingredient of [[chocolate]], a source of polyphenols.]]
There is  debate regarding the total body absorption of dietary intake of polyphenolic compounds.  While some indicate potential health effects of certain specific polyphenols, most studies demonstrate low [[bioavailability]] and rapid excretion of polyphenols, indicating their potential roles only in small concentrations in vivo.<ref name=lpi/><ref name=Williams/><ref name=Frei/><ref name=Virgili/> More research is needed to understand the interactions between a variety of these chemicals acting in concert within the human body.<ref name=lpi/>
== Topical application of polyphenols ==
There is no substantial evidence that reactive oxygen species play a role in the process of skin [[ageing|aging]].<ref name=podda>{{cite journal |vauthors=Podda M, Grundmann-Kollmann M |title=Low molecular weight antioxidants and their role in skin ageing |journal= Clinical and Experimental Dermatology|volume=26 |issue=7 |pages=578–82 |date=October 2001 |pmid=11696061 |doi=10.1046/j.1365-2230.2001.00902.x|s2cid=19659324 }}</ref> The skin is exposed to various [[exogenous]] sources of [[oxidative stress]], including [[ultraviolet]] radiation whose spectral components may be responsible for the [[extrinsic]] type of skin aging, sometimes termed [[photoaging]]. Controlled long-term studies on the efficacy of low molecular weight antioxidants in the prevention or treatment of [[human skin|skin]] aging in humans are absent.
== Combination of antioxidants in vitro==
Experiments on [[linoleic acid]] subjected to [[2,2′-azobis (2-amidinopropane) dihydrochloride]]-induced oxidation with different combinations of phenolics show that binary mixtures can lead to either a [[synergy|synergetic]] effect or to an [[Antagonism (chemistry)|antagonistic]] effect.<ref>{{Cite journal | doi=10.1007/s11746-003-0812-z| title=Antioxidant activity of phenolic compounds in 2,2′-azobis (2-amidinopropane) dihydrochloride (AAPH)-induced oxidation: Synergistic and antagonistic effects| journal=Journal of the American Oil Chemists' Society| volume=80| issue=10| pages=1007| year=2003| last1=Peyrat-Maillard| first1=M. N.| last2=Cuvelier| first2=M. E.| last3=Berset| first3=C.| s2cid=86810404}}</ref>
Antioxidant levels of purified anthocyanin extracts were much higher than expected from anthocyanin content indicating [[synergy|synergistic]] effect of anthocyanin mixtures.<ref>{{Cite journal |doi = 10.1021/jf0204811|pmid = 12358498|title = Color and Antioxidant Properties of Cyanidin-Based Anthocyanin Pigments|journal = Journal of Agricultural and Food Chemistry|volume = 50|issue = 21|pages = 6172–81|year = 2002|last1 = Stintzing|first1 = Florian C.|last2 = Stintzing|first2 = Angela S.|last3 = Carle|first3 = Reinhold|last4 = Frei|first4 = Balz|last5 = Wrolstad|first5 = Ronald E.}}</ref>
== Antioxidant capacity tests ==
* [[Oxygen radical absorbance capacity]] (ORAC)<ref name=USDAx/>
* [[Ferricyanide]] reducing power
* [[2,2-diphenyl-1-picrylhydrazyl]] radical scavenging activity<ref>{{Cite journal | doi=10.1016/j.chroma.2007.10.080| pmid=18035361| title=Characterization of monomeric and oligomeric flavan-3-ols from barley and malt by liquid chromatography–ultraviolet detection–electrospray ionization mass spectrometry| journal=Journal of Chromatography A| volume=1189| issue=1–2| pages=398–405| year=2008| last1=Dvorakova| first1=Marketa| last2=Moreira| first2=Manuela M.| last3=Dostalek| first3=Pavel| last4=Skulilova| first4=Zuzana| last5=Guido| first5=Luís F.| last6=Barros| first6=Aquiles A.}}</ref>
== See also ==
* [[List of phytochemicals in food]]
* [[List of antioxidants in food]]
* [[Health effects of polyphenols]]
* [[Free-radical theory]]
* [[Nitric oxide]]
* [[Resveratrol]]
* [[Astaxanthin]]
== References==
{{Reflist|30em}}
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{{Antioxidants}}
{{DEFAULTSORT:Polyphenol Antioxidant}}
[[Category:Angiology]]
[[Category:Chemopreventive agents]]
[[Category:Polyphenols| ]]
[[Category:Antioxidants]]