Editing Polyphenol (section)

===Reactivity===
Polyphenols readily react with metal ions to form [[coordination complexes]], some of which form [[Metal-phenolic network|Metal-phenolic Networks]].<ref>{{Cite journal |last=Geng |first=Huimin |title=Metal Ion-Directed Functional Metal−Phenolic Materials |url=https://pubs.acs.org/doi/abs/10.1021/acs.chemrev.1c01042 |journal=Chemical Reviews |volume=122 |pages=11432-11473 |doi=10.1021/acs.chemrev.1c01042|url-access=subscription }}</ref>

====Extraction====
[[Extraction (chemistry)|Extraction]] of polyphenols<ref>{{cite book| vauthors = Escribano-Bailon MT, Santos-Buelga C |chapter=Polyphenol Extraction From Foods | veditors = Santos-Buelga C, Williamson G |title=Methods in Polyphenol Analysis|publisher=Royal Society of Chemistry|year=2003|isbn=978-0-85404-580-8|pages=1–16|chapter-url=http://kurdchemists.org/files/Polyphenols.pdf}}</ref> can be performed using a solvent like water, [[hot water extraction|hot water]], methanol, methanol/formic acid, methanol/water/acetic or formic acid. [[Liquid–liquid extraction]] can be also performed or [[countercurrent chromatography]]. [[Solid phase extraction]] can also be made on C18 sorbent cartridges. Other techniques are ultrasonic extraction, heat reflux extraction, microwave-assisted extraction,<ref>{{cite journal| vauthors = Pan X |year=2003|title=Microwave-assisted extraction of tea polyphenols and tea caffeine from green tea leaves|journal=Chemical Engineering and Processing|volume=42|issue=2|pages=129–133|doi=10.1016/S0255-2701(02)00037-5|bibcode=2003CEPPI..42..129P }}</ref> [[critical carbon dioxide]],<ref name=":0">{{cite journal | vauthors = Aizpurua-Olaizola O, Ormazabal M, Vallejo A, Olivares M, Navarro P, Etxebarria N, Usobiaga A | title = Optimization of supercritical fluid consecutive extractions of fatty acids and polyphenols from ''Vitis vinifera'' grape wastes | journal = Journal of Food Science | volume = 80 | issue = 1 | pages = E101–E107 | date = January 2015 | pmid = 25471637 | doi = 10.1111/1750-3841.12715 }}</ref><ref>{{cite journal | vauthors = Palma M, Taylor LT | title = Extraction of polyphenolic compounds from grape seeds with near critical carbon dioxide | journal = Journal of Chromatography A | volume = 849 | issue = 1 | pages = 117–124 | date = July 1999 | pmid = 10444839 | doi = 10.1016/S0021-9673(99)00569-5 }}</ref> high-pressure [[Extract#Extraction techniques|liquid extraction]]<ref>{{cite journal | vauthors = Alonso-Salces RM, Korta E, Barranco A, Berrueta LA, Gallo B, Vicente F | title = Pressurized liquid extraction for the determination of polyphenols in apple | journal = Journal of Chromatography A | volume = 933 | issue = 1–2 | pages = 37–43 | date = November 2001 | pmid = 11758745 | doi = 10.1016/S0021-9673(01)01212-2 }}</ref> or use of ethanol in an immersion extractor.<ref>{{cite journal| vauthors = Sineiro J, Domínguez H, Núñez MJ, Lema JM |year=1996|title=Ethanol extraction of polyphenols in an immersion extractor. Effect of pulsing flow|journal=Journal of the American Oil Chemists' Society|volume=73|issue=9|pages=1121–1125|doi=10.1007/BF02523372|s2cid=96009875}}</ref> The extraction conditions (temperature, extraction time, ratio of solvent to raw material, particle size of the sample, solvent type, and solvent concentrations) for different raw materials and extraction methods have to be optimized.<ref name=papoutsis2018a>{{cite journal|title=Screening the effect of four ultrasound-assisted extraction parameters on hesperidin and phenolic acid content of aqueous citrus pomace extracts|journal=Food Bioscience|date=2018|pages=20–26|volume=21|last1=Papoutsis|doi=10.1016/j.fbio.2017.11.001|first1=Konstantinos |last2=Pristijono |first2=Penta |last3=Golding |first3=John |last4=Stathopoulos |first4=Costas |last5=Bowyer |first5=Michael |last6=Scarlett |first6=Christopher |last7=Vuong |first7=Quan|url=https://rke.abertay.ac.uk/ws/files/14225156/Stathopoulos_ScreeningTheEffectOfFourUltrasound_AssistedExtractionParameters_Author_2017.pdf }}</ref><ref name=papoutsis2018b>{{cite journal|title=Pretreatment of citrus by-products affects polyphenol recovery: a review|journal=Food Reviews International|date=2018|pages=770–795|volume=34|last1=Papoutsis|doi=10.1080/87559129.2018.1438471|first1=Konstantinos |last2=Vuong |first2=Quan |last3=Golding |first3=John |last4=Hasperué |first4=Joaquín |last5=Pristijono |first5=Penta |last6=Bowyer |first6=Michael |last7=Scarlett |first7=Christopher |last8=Stathopoulos |first8=Costas|issue=8 |hdl=11336/87660 |s2cid=89981908 |url=https://rke.abertay.ac.uk/ws/files/14378631/Stathopoulos_PretreatmentOfCitrusBy_ProductsAffectsPolyphenolRecovery_Author_2018.pdf }}</ref>

Mainly found in the fruit skins and seeds, high levels of polyphenols may reflect only the ''measured extractable'' polyphenol (EPP) content of a fruit which may also contain non-extractable polyphenols. Black tea contains high amounts of polyphenol and makes up for 20% of its weight.<ref>{{cite journal | vauthors = Arranz S, Saura-Calixto F, Shaha S, Kroon PA | title = High contents of nonextractable polyphenols in fruits suggest that polyphenol contents of plant foods have been underestimated | journal = Journal of Agricultural and Food Chemistry | volume = 57 | issue = 16 | pages = 7298–7303 | date = August 2009 | pmid = 19637929 | doi = 10.1021/jf9016652 | hdl = 10261/82508 }}</ref>

Concentration can be made by [[ultrafiltration]].<ref>{{cite journal| vauthors = Nawaz H, Shi J, Mittal GS, Kakuda Y |year=2006|title=Extraction of polyphenols from grape seeds and concentration by ultrafiltration|journal=Separation and Purification Technology|volume=48|issue=2|pages=176–181|doi=10.1016/j.seppur.2005.07.006}}</ref> Purification can be achieved by [[preparative chromatography]].

====Analysis techniques====
[[File:RP HPLC.PNG|thumb|right|Reversed-phase HPLC plot of separation of phenolic compounds. Smaller [[natural phenol]]s formed individual peaks while [[tannin]]s form a ''hump''.]]

[[Phosphomolybdic acid]] is used as a reagent for staining phenolics in [[thin layer chromatography]]. Polyphenols can be studied by [[spectroscopy]], especially in the ultraviolet domain, by [[fractionation]] or [[paper chromatography]]. They can also be analysed by chemical characterisation.

[[Instrumental chemistry]] analyses include [[Separation process|separation]] by [[high performance liquid chromatography]] (HPLC), and especially by [[reversed-phase liquid chromatography]] (RPLC), can be coupled to [[mass spectrometry]].<ref name=":0" />

=====Microscopy analysis=====
The [[DMACA reagent]] is an histological dye specific to polyphenols used in microscopy analyses. The [[autofluorescence]] of polyphenols can also be used, especially for localisation of lignin and [[suberin]].  Where fluorescence of the molecules themselves is insufficient for visualization by light microscopy, DPBA (diphenylboric acid 2-aminoethyl ester, also referred to as Naturstoff reagent A) has traditionally been used, at least in [[Botany|plant science]], to enhance the fluorescence signal.<ref>{{cite journal | vauthors = Ferrara BT, Thompson EP | title = A method for visualizing fluorescence of flavonoid therapeutics in vivo in the model eukaryote Dictyostelium discoideum | journal = BioTechniques | volume = 66 | issue = 2 | pages = 65–71 | date = February 2019 | pmid = 30744410 | doi = 10.2144/btn-2018-0084 | type = Paper | doi-access = free }}{{open access}}</ref>

==== Quantification ====
Polyphenolic content in vitro can be quantified by [[volumetric titration]]. An oxidizing agent, [[permanganate]], is used to oxidize known concentrations of a standard tannin solution, producing a [[standard curve]]. The tannin content of the unknown is then expressed as equivalents of the appropriate hydrolyzable or condensed tannin.<ref>{{cite journal | vauthors = Tempel AS | title = Tannin-measuring techniques : A review | journal = Journal of Chemical Ecology | volume = 8 | issue = 10 | pages = 1289–1298 | date = October 1982 | pmid = 24414735 | doi = 10.1007/BF00987762 | bibcode = 1982JCEco...8.1289T | s2cid = 39848160 }}</ref>

Some methods for quantification of total polyphenol content in vitro are based on [[colorimetry|colorimetric]] measurements. Some tests are relatively specific to polyphenols (for instance the Porter's assay). Total phenols (or antioxidant effect) can be measured using the [[Folin–Ciocalteu reaction]].<ref name=":0" /> Results are typically expressed as gallic acid equivalents. Polyphenols are seldom evaluated by [[antibody]] technologies.<ref>{{Cite journal| vauthors = Gani M, Mcguinness BJ, Da Vies AP |year=1998|title=Monoclonal antibodies against tea polyphenols: A novel immunoassay to detect polyphenols in biological fluids|journal=Food and Agricultural Immunology|volume=10|pages=13–22|doi=10.1080/09540109809354964}}</ref>

Other tests measure the antioxidant capacity of a fraction. Some make use of the [[ABTS]] radical [[cation]] which is reactive towards most antioxidants including phenolics, [[thiol]]s and [[vitamin C]].<ref>{{cite journal | vauthors = Walker RB, Everette JD | title = Comparative reaction rates of various antioxidants with ABTS radical cation | journal = Journal of Agricultural and Food Chemistry | volume = 57 | issue = 4 | pages = 1156–1161 | date = February 2009 | pmid = 19199590 | doi = 10.1021/jf8026765 }}</ref> During this reaction, the blue ABTS radical cation is converted back to its colorless neutral form. The reaction may be monitored spectrophotometrically. This assay is often referred to as the [[Trolox equivalent antioxidant capacity]] (TEAC) assay. The reactivity of the various antioxidants tested are compared to that of [[Trolox]], which is a [[vitamin E]] analog.

Other antioxidant capacity assays which use Trolox as a standard include the [[diphenylpicrylhydrazyl]] (DPPH), [[oxygen radical absorbance capacity]] (ORAC),<ref>{{cite journal | vauthors = Roy MK, Koide M, Rao TP, Okubo T, Ogasawara Y, Juneja LR | title = ORAC and DPPH assay comparison to assess antioxidant capacity of tea infusions: relationship between total polyphenol and individual catechin content | journal = International Journal of Food Sciences and Nutrition | volume = 61 | issue = 2 | pages = 109–124 | date = March 2010 | pmid = 20109129 | doi = 10.3109/09637480903292601 | s2cid = 1929167 }}</ref> [[ferric reducing ability of plasma]] (FRAP)<ref>{{cite journal | vauthors = Pulido R, Bravo L, Saura-Calixto F | title = Antioxidant activity of dietary polyphenols as determined by a modified ferric reducing/antioxidant power assay | journal = Journal of Agricultural and Food Chemistry | volume = 48 | issue = 8 | pages = 3396–3402 | date = August 2000 | pmid = 10956123 | doi = 10.1021/jf9913458 | hdl-access = free | hdl = 10261/112476 }}</ref> assays or inhibition of copper-catalyzed ''in vitro'' human [[low-density lipoprotein]] oxidation.<ref>{{Cite journal| vauthors = Meyer AS, Yi OS, Pearson DA, Waterhouse AL, Frankel EN |year=1997|title=Inhibition of Human Low-Density Lipoprotein Oxidation in Relation to Composition of Phenolic Antioxidants in Grapes (Vitis vinifera)|journal=Journal of Agricultural and Food Chemistry|volume=45|issue=5|pages=1638–1643|doi=10.1021/jf960721a}}</ref>

New methods including the use of [[biosensor]]s can help monitor the content of polyphenols in food.<ref>{{cite journal| vauthors = Mello LD, Sotomayor MD, Kubota LT |year=2003|title=HRP-based amperometric biosensor for the polyphenols determination in vegetables extract|journal=Sensors and Actuators B: Chemical|volume=96|issue=3|pages=636–645|doi=10.1016/j.snb.2003.07.008|bibcode=2003SeAcB..96..636M }}</ref>

Quantitation results produced by the mean of [[diode array detector]]–coupled HPLC are generally given as relative rather than [[absolute value]]s as there is a lack of commercially available [[Standard (metrology)|standards]] for all polyphenolic molecules.{{Citation needed|date=July 2021}}