flavonoid

In the 1930s, Albert Szent-Györgyi and other scientists discovered that Vitamin C alone was not as effective at preventing scurvy as the crude yellow extract from oranges, lemons or paprika. They attributed the increased activity of this extract to the other substances in this mixture, which they referred to as "citrin" (referring to citrus) or "Vitamin P" (a reference to its effect on reducing the permeability of capillaries). The substances in question (hesperidin, eriodictyol, hesperidin methyl chalcone and neohesperidin) were however later shown not to fulfil the criteria of a vitamin,{{Cite book|url=https://books.google.com/books?id=hc1TyKSumOkC&pg=PA210|title=Vitamins and Hormones|date=1949|publisher=Academic Press|isbn=978-0-08-086604-8|language=en}} so that this term is now obsolete.{{Cite book|vauthors=Clemetson AB|url=https://books.google.com/books?id=1kgPEAAAQBAJ&pg=PA101|title=Vitamin C: Volume I|date=January 10, 2018|publisher=CRC Press|isbn=978-1-351-08601-1|language=en}}

{{Main|Flavonoid biosynthesis}}

Flavonoids are secondary metabolites synthesized mainly by plants. The general structure of flavonoids is a fifteen-carbon skeleton, containing two benzene rings connected by a three-carbon linking chain. Therefore, they are depicted as C6-C3-C6 compounds. Depending on the chemical structure, degree of oxidation, and unsaturation of the linking chain (C3), flavonoids can be classified into different groups, such as anthocyanidins, flavonols, flavanones, flavan-3-ols, flavanonols, flavones, and isoflavones. Chalcones, also called chalconoids, although lacking the heterocyclic ring, are also classified as flavonoids. Furthermore, flavonoids can be found in plants in glycoside-bound and free aglycone forms. The glycoside-bound form is the most common flavone and flavonol form consumed in the diet.

File:Flavonoids Biochemistry.png

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Flavonoids are widely distributed in plants, fulfilling many functions. They are the most important plant pigments for flower coloration, producing yellow or red/blue pigmentation in petals evolved to attract pollinator animals. In higher plants, they are involved in UV filtration, symbiotic nitrogen fixation, and floral pigmentation. They may also act as chemical messengers, physiological regulators, and cell cycle inhibitors. Flavonoids secreted by the root of their host plant help Rhizobia in the infection stage of their symbiotic relationship with legumes like peas, beans, clover, and soy. Rhizobia living in soil are able to sense the flavonoids and this triggers the secretion of Nod factors, which in turn are recognized by the host plant and can lead to root hair deformation and several cellular responses such as ion fluxes and the formation of a root nodule. In addition, some flavonoids have inhibitory activity against organisms that cause plant diseases, e.g. Fusarium oxysporum.{{cite journal|doi=10.1016/j.phytol.2007.10.001|title=Flavonoids from carnation (Dianthus caryophyllus) and their antifungal activity|year=2008| vauthors = Galeotti F, Barile E, Curir P, Dolci M, Lanzotti V |journal=Phytochemistry Letters|volume=1|issue=1 |pages=44–48|bibcode=2008PChL....1...44G }}

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{{cite journal | vauthors = Ververidis F, Trantas E, Douglas C, Vollmer G, Kretzschmar G, Panopoulos N | title = Biotechnology of flavonoids and other phenylpropanoid-derived natural products. Part I: Chemical diversity, impacts on plant biology and human health | journal = Biotechnology Journal | volume = 2 | issue = 10 | pages = 1214–1234 | date = October 2007 | pmid = 17935117 | doi = 10.1002/biot.200700084 | s2cid = 24986941 }}):

File:Flavonoids.svg

File:Flavylium cation.svg

Anthocyanidins are the aglycones of anthocyanins; they use the flavylium (2-phenylchromenylium) ion skeleton.

:Examples: cyanidin, delphinidin, malvidin, pelargonidin, peonidin, petunidin

Anthoxanthins are divided into two groups:{{cite journal|title=Isolation of a UDP-glucose: Flavonoid 5-O-glucosyltransferase gene and expression analysis of anthocyanin biosynthetic genes in herbaceous peony (Paeonia lactiflora Pall.) |vauthors=Zhao DQ, Han CX, Ge JT, Tao J |journal=Electronic Journal of Biotechnology |date=November 15, 2012 |volume=15 |issue=6 |doi=10.2225/vol15-issue6-fulltext-7}}

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Flavanones

Flavanonols

File:Flavan acsv.svg

Include flavan-3-ols (flavanols), flavan-4-ols, and flavan-3,4-diols.

• Flavan-3-ols (flavanols)
• Flavan-3-ols use the 2-phenyl-3,4-dihydro-2H-chromen-3-ol skeleton
• :Examples: catechin (C), gallocatechin (GC), catechin 3-gallate (Cg), gallocatechin 3-gallate (GCg), epicatechins (EC), epigallocatechin (EGC), epicatechin 3-gallate (ECg), epigallocatechin 3-gallate (EGCg)
• Theaflavin
• :Examples: theaflavin-3-gallate, theaflavin-3'-gallate, theaflavin-3,3'-digallate
• Thearubigin
• Proanthocyanidins are dimers, trimers, oligomers, or polymers of the flavanols

• Isoflavonoids
• Isoflavones use the 3-phenylchromen-4-one skeleton (with no hydroxyl group substitution on carbon at position 2)
• :Examples: Genistein, Daidzein, Glycitein
• Isoflavanes
• Isoflavandiols
• Isoflavenes
• Coumestans
• Pterocarpans

Image:Parsley100.jpg]]

Image:PattsBlueberries.jpg

Image:Grapefruit Schnitt 2008-3-3.JPG fruits, including red grapefruit]]

Flavonoids (specifically flavanoids such as the catechins) are "the most common group of polyphenolic compounds in the human diet and are found ubiquitously in plants".{{cite journal | vauthors = Spencer JP | title = Flavonoids: modulators of brain function? | journal = The British Journal of Nutrition | volume = 99 |issue= E Suppl 1 | pages = ES60–ES77 | date = May 2008 | pmid = 18503736 | doi = 10.1017/S0007114508965776 | doi-access = free }} Flavonols, the original bioflavonoids such as quercetin, are also found ubiquitously, but in lesser quantities. The widespread distribution of flavonoids, their variety and their relatively low toxicity compared to other active plant compounds (for instance alkaloids) mean that many animals, including humans, ingest significant quantities in their diet.

Foods with a high flavonoid content include parsley, onions, blueberries and strawberries, black tea, bananas, and citrus fruits.{{cite web |url=http://www.ars.usda.gov/SP2UserFiles/Place/12354500/Articles/AICR06_flav.pdf|title=Sources of Flavonoids in the U.S. Diet Using USDA’s Updated Database on the Flavonoid Content of Selected Foods|publisher=Agricultural Research Service, US Department of Agirculture|date=2006}} One study found high flavonoid content in buckwheat.{{Cite journal| vauthors = Oomah BD, Mazza G |title=Flavonoids and Antioxidative Activities in Buckwheat|journal=Journal of Agricultural and Food Chemistry|volume=44|issue=7|pages=1746–1750 |doi=10.1021/jf9508357 |year=1996}}

Citrus flavonoids include hesperidin (a glycoside of the flavanone hesperetin), quercitrin, rutin (two glycosides of quercetin, and the flavone tangeritin. The flavonoids are less concentrated in the pulp than in the peels (for example, 165 versus 1156 mg/100 g in pulp versus peel of satsuma mandarin, and 164 vis-à-vis 804 mg/100 g in pulp versus peel of clementine).{{cite journal|url=http://www.agr.unizg.hr/smotra/pdf_74/acs74_38.pdf|title=Determination of flavonoids in pulp and peel of mandarin fruits (table 1)|page=223|journal=Agriculturae Conspectus Scientificus|year=2009|volume=74|number=3|vauthors=Levaj B|display-authors=etal|access-date=2020-07-31|archive-date=2017-08-10|archive-url=https://web.archive.org/web/20170810141820/http://www.agr.unizg.hr/smotra/pdf_74/acs74_38.pdf|url-status=dead}}

Peanut (red) skin contains significant polyphenol content, including flavonoids.{{cite journal | vauthors = De Camargo AC, Regitano-d'Arce MA, Gallo CR, Shahidi F | year = 2015 | title = Gamma-irradiation induced changes in microbiological status, phenolic profile and antioxidant activity of peanut skin | journal = Journal of Functional Foods | volume = 12 | pages = 129–143 | doi=10.1016/j.jff.2014.10.034| doi-access = free }}{{cite journal | vauthors = Chukwumah Y, Walker LT, Verghese M | title = Peanut skin color: a biomarker for total polyphenolic content and antioxidative capacities of peanut cultivars | journal = International Journal of Molecular Sciences | volume = 10 | issue = 11 | pages = 4941–4952 | date = November 2009 | pmid = 20087468 | pmc = 2808014 | doi = 10.3390/ijms10114941 | doi-access = free }}

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File:Flavonoid intake of adults (18 to 64 years) in the European Union.png

Food composition data for flavonoids were provided by the USDA database on flavonoids. In the United States NHANES survey, mean flavonoid intake was 190 mg per day in adults, with flavan-3-ols as the main contributor.{{cite journal | vauthors = Chun OK, Chung SJ, Song WO | title = Estimated dietary flavonoid intake and major food sources of U.S. adults | journal = The Journal of Nutrition | volume = 137 | issue = 5 | pages = 1244–1252 | date = May 2007 | pmid = 17449588 | doi = 10.1093/jn/137.5.1244 | doi-access = free }} In the European Union, based on data from EFSA, mean flavonoid intake was 140 mg/d, although there were considerable differences among individual countries.{{cite journal | vauthors = Vogiatzoglou A, Mulligan AA, Lentjes MA, Luben RN, Spencer JP, Schroeter H, Khaw KT, Kuhnle GG | display-authors = 6 | title = Flavonoid intake in European adults (18 to 64 years) | journal = PLOS ONE | volume = 10 | issue = 5 | pages = e0128132 | year = 2015 | pmid = 26010916 | pmc = 4444122 | doi = 10.1371/journal.pone.0128132 | bibcode = 2015PLoSO..1028132V | doi-access = free }} The main type of flavonoids consumed in the EU and USA were flavan-3-ols (80% for USA adults), mainly from tea or cocoa in chocolate, while intake of other flavonoids was considerably lower.

File:Main types and sources of flavonoids consumed by adults (18 to 64 years) in the European Union.png

Neither the United States Food and Drug Administration (FDA) nor the European Food Safety Authority (EFSA) has approved any flavonoids as prescription drugs.{{cite web |url=http://www.accessdata.fda.gov/scripts/cder/drugsatfda/index.cfm|title=FDA approved drug products |publisher=US Food and Drug Administration|access-date=November 8, 2013}}{{cite web |url=https://www.fda.gov/Food/IngredientsPackagingLabeling/LabelingNutrition/ucm2006876.htm#Approved_Health_Claims|title=Health Claims Meeting Significant Scientific Agreement |publisher=US Food and Drug Administration |access-date=November 8, 2013}}{{cite journal |author=EFSA Panel on Dietetic Products, Nutrition and Allergies (NDA) |title=Scientific Opinion on the substantiation of health claims related to various food(s)/food constituent(s) and protection of cells from premature aging, antioxidant activity, antioxidant content and antioxidant properties, and protection of DNA, proteins and lipids from oxidative damage pursuant to Article 13(1) of Regulation (EC) No 1924/20061|journal= EFSA Journal|year= 2010|volume= 8|issue=2|page=1489|doi=10.2903/j.efsa.2010.1489|doi-access=free}} The U.S. FDA has warned numerous dietary supplement and food manufacturers, including Unilever, producer of Lipton tea in the U.S., about illegal advertising and misleading health claims regarding flavonoids, such as that they lower cholesterol or relieve pain.{{cite news |url=https://www.npr.org/sections/health-shots/2010/09/07/129701566/fda-to-lipton-tea-can-t-do-that |title=FDA To Lipton: Tea Can't Do That |author=Hensley S |date=September 7, 2010 |website=NPR |access-date=June 17, 2023}}{{cite news |url=https://theproducenews.com/cherry-companies-warned-fda-against-making-health-claims |title=Cherry companies warned by FDA against making health claims |author= |date=November 1, 2005 |website=The Produce News |access-date=June 17, 2023}}

Flavonoids are poorly absorbed in the human body (less than 5%), then are quickly metabolized into smaller fragments with unknown properties, and rapidly excreted.{{cite journal | vauthors = Lotito SB, Frei B | title = Consumption of flavonoid-rich foods and increased plasma antioxidant capacity in humans: cause, consequence, or epiphenomenon? | journal = Free Radical Biology & Medicine | volume = 41 | issue = 12 | pages = 1727–1746 | date = December 2006 | pmid = 17157175 | doi = 10.1016/j.freeradbiomed.2006.04.033 }}{{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 = 838–849 | date = April 2004 | pmid = 15019969 | doi = 10.1016/j.freeradbiomed.2004.01.001 }} Flavonoids have negligible antioxidant activity in the body, and the increase in antioxidant capacity of blood seen after consumption of flavonoid-rich foods is not caused directly by flavonoids, but by production of uric acid resulting from flavonoid depolymerization and excretion. Microbial metabolism is a major contributor to the overall metabolism of dietary flavonoids.{{cite journal | vauthors = Hidalgo M, Oruna-Concha MJ, Kolida S, Walton GE, Kallithraka S, Spencer JP, de Pascual-Teresa S | title = Metabolism of anthocyanins by human gut microflora and their influence on gut bacterial growth | journal = Journal of Agricultural and Food Chemistry | volume = 60 | issue = 15 | pages = 3882–3890 | date = April 2012 | pmid = 22439618 | doi = 10.1021/jf3002153 }}

Inflammation has been implicated as a possible origin of numerous local and systemic diseases, such as cancer,{{cite journal | vauthors = Ravishankar D, Rajora AK, Greco F, Osborn HM | title = Flavonoids as prospective compounds for anti-cancer therapy | journal = The International Journal of Biochemistry & Cell Biology | volume = 45 | issue = 12 | pages = 2821–2831 | date = December 2013 | pmid = 24128857 | doi = 10.1016/j.biocel.2013.10.004 }} cardiovascular disorders,{{cite journal | vauthors = Manach C, Mazur A, Scalbert A | title = Polyphenols and prevention of cardiovascular diseases | journal = Current Opinion in Lipidology | volume = 16 | issue = 1 | pages = 77–84 | date = February 2005 | pmid = 15650567 | doi = 10.1097/00041433-200502000-00013 | s2cid = 794383 }} diabetes mellitus,{{cite journal | vauthors = Babu PV, Liu D, Gilbert ER | title = Recent advances in understanding the anti-diabetic actions of dietary flavonoids | journal = The Journal of Nutritional Biochemistry | volume = 24 | issue = 11 | pages = 1777–1789 | date = November 2013 | pmid = 24029069 | pmc = 3821977 | doi = 10.1016/j.jnutbio.2013.06.003 }} and celiac disease.{{cite journal | vauthors = Ferretti G, Bacchetti T, Masciangelo S, Saturni L | title = Celiac disease, inflammation and oxidative damage: a nutrigenetic approach | journal = Nutrients | volume = 4 | issue = 4 | pages = 243–257 | date = April 2012 | pmid = 22606367 | pmc = 3347005 | doi = 10.3390/nu4040243 | doi-access = free }} There is no clinical evidence that dietary flavonoids affect any of these diseases.

Clinical studies investigating the relationship between flavonoid consumption and cancer prevention or development are conflicting for most types of cancer, probably because most human studies have weak designs, such as a small sample size.{{cite journal | vauthors = Romagnolo DF, Selmin OI | title = Flavonoids and cancer prevention: a review of the evidence | journal = Journal of Nutrition in Gerontology and Geriatrics | volume = 31 | issue = 3 | pages = 206–238 | year = 2012 | pmid = 22888839 | doi = 10.1080/21551197.2012.702534 | s2cid = 205960210 }} There is little evidence to indicate that dietary flavonoids affect human cancer risk in general.

Although no significant association has been found between flavan-3-ol intake and cardiovascular disease mortality, clinical trials have shown improved endothelial function and reduced blood pressure (with a few studies showing inconsistent results). Reviews of cohort studies in 2013 found that the studies had too many limitations to determine a possible relationship between increased flavonoid intake and decreased risk of cardiovascular disease, although a trend for an inverse relationship existed.{{cite journal | vauthors = Wang X, Ouyang YY, Liu J, Zhao G | title = Flavonoid intake and risk of CVD: a systematic review and meta-analysis of prospective cohort studies | journal = The British Journal of Nutrition | volume = 111 | issue = 1 | pages = 1–11 | date = January 2014 | pmid = 23953879 | doi = 10.1017/S000711451300278X | doi-access = free }}

In 2013, the EFSA decided to permit health claims that 200 mg/day of cocoa flavanols "help[s] maintain the elasticity of blood vessels."{{cite journal |author= |date=June 27, 2012 |title=Scientific Opinion on the substantiation of a health claim related to cocoa flavanols and maintenance of normal endothelium-dependent vasodilation pursuant to Article 13(5) of Regulation (EC) No 1924/2006 |url=https://www.efsa.europa.eu/pt/efsajournal/pub/2809 |journal=EFSA Journal |volume=10 |issue=7 |doi=10.2903/j.efsa.2012.2809 |access-date=June 17, 2023}}{{cite web |url=https://www.confectionerynews.com/Article/2013/09/04/Cocoa-flavanol-health-claim-becomes-EU-law |title=Cocoa flavanol health claim becomes EU law |author= |date=September 4, 2013 |website=Confectionary News |access-date=June 17, 2023}} The FDA followed suit in 2023, stating that there is "supportive, but not conclusive" evidence that 200 mg per day of cocoa flavanols can reduce the risk of cardiovascular disease. This is greater than the levels found in typical chocolate bars, which can also contribute to weight gain, potentially harming cardiovascular health.{{cite report |author=Kavanaugh C |date=February 1, 2023 |title=RE: Petition for a Qualified Health Claim – for Cocoa Flavanols and Reduced Risk of Cardiovascular Disease (Docket No. FDA-2019-Q-0806)

|url=https://www.fda.gov/media/165090/download |publisher=FDA}}{{cite news |url=https://www.npr.org/sections/health-shots/2023/02/12/1156044919/chocolate-heart-health-flavanols |title=Is chocolate good for your heart? Finally the FDA has an answer – kind of |author=Aubrey A |date=February 12, 2023 |website=NPR |access-date=June 17, 2023}}

Flavonoid synthesis in plants is induced by light color spectrums at both high and low energy radiations. Low energy radiations are accepted by phytochrome, while high energy radiations are accepted by carotenoids, flavins, cryptochromes in addition to phytochromes. The photomorphogenic process of phytochrome-mediated flavonoid biosynthesis has been observed in Amaranthus, barley, maize, Sorghum and turnip. Red light promotes flavonoid synthesis.{{Cite book|title = Modern Plant Physiology|url = https://books.google.com/books?id=03S6VbTjCmUC|publisher = CRC Press|date = January 2004|isbn = 9780849317149|language = en | vauthors = Sinha RK |page = 457}}

Research has shown production of flavonoid molecules from genetically engineered microorganisms.{{cite journal | vauthors = Trantas E, Panopoulos N, Ververidis F | title = Metabolic engineering of the complete pathway leading to heterologous biosynthesis of various flavonoids and stilbenoids in Saccharomyces cerevisiae | journal = Metabolic Engineering | volume = 11 | issue = 6 | pages = 355–366 | date = November 2009 | pmid = 19631278 | doi = 10.1016/j.ymben.2009.07.004 }}{{cite journal | vauthors = Ververidis F, Trantas E, Douglas C, Vollmer G, Kretzschmar G, Panopoulos N | title = Biotechnology of flavonoids and other phenylpropanoid-derived natural products. Part II: Reconstruction of multienzyme pathways in plants and microbes | journal = Biotechnology Journal | volume = 2 | issue = 10 | pages = 1235–1249 | date = October 2007 | pmid = 17935118 | doi = 10.1002/biot.200700184 | s2cid = 5805643 }}

Four pieces of magnesium filings are added to the ethanolic extract followed by few drops of concentrated hydrochloric acid. A pink or red colour indicates the presence of flavonoid.{{cite journal|vauthors=Yisa J |title=Phytochemical Analysis and Antimicrobial Activity of Scoparia dulcis and Nymphaea lotus|url=http://connection.ebscohost.com/c/articles/51366872/phytochemical-analysis-antimicrobial-activity-scoparia-dulcis-nymphaea-lotus|archive-url=https://web.archive.org/web/20131017003142/http://connection.ebscohost.com/c/articles/51366872/phytochemical-analysis-antimicrobial-activity-scoparia-dulcis-nymphaea-lotus|url-status=dead|archive-date=October 17, 2013|journal=Australian Journal of Basic and Applied Sciences|year= 2009|volume= 3|issue=4|pages=3975–3979}} Colours varying from orange to red indicated flavones, red to crimson indicated flavonoids, crimson to magenta indicated flavonones.

About 5 mg of the compound is dissolved in water, warmed, and filtered. 10% aqueous sodium hydroxide is added to 2 ml of this solution. This produces a yellow coloration. A change in color from yellow to colorless on addition of dilute hydrochloric acid is an indication for the presence of flavonoids.{{cite journal | vauthors = Bello IA, Ndukwe GI, Audu OT, Habila JD | title = A bioactive flavonoid from Pavetta crassipes K. Schum. | journal = Organic and Medicinal Chemistry Letters | volume = 1 | issue = 1 | pages = 14 | date = October 2011 | pmid = 22373191 | pmc = 3305906 | doi = 10.1186/2191-2858-1-14 | doi-access = free }}

A colorimetric assay based upon the reaction of A-rings with the chromogen p-dimethylaminocinnamaldehyde (DMACA) has been developed for flavanoids in beer that can be compared with the vanillin procedure.{{cite journal | doi = 10.1002/j.2050-0416.1985.tb04303.x | volume=91 | year=1985 | journal=Journal of the Institute of Brewing | pages=37–40 | vauthors=Delcour JA| title=A New Colourimetric Assay for Flavanoids in Pilsner Beers | doi-access=free }}

Lamaison and Carnet have designed a test for the determination of the total flavonoid content of a sample (AlCI₃ method). After proper mixing of the sample and the reagent, the mixture is incubated for ten minutes at ambient temperature and the absorbance of the solution is read at 440 nm. Flavonoid content is expressed in mg/g of quercetin.{{cite journal|vauthors=Lamaison JL, Carnet A |title=Teneurs en principaux flavonoïdes des fleurs de Cratageus monogyna Jacq. et de Cratageus laevigata (Poiret D.C.) en fonction de la végétation|trans-title=Principal flavonoid content of flowers of Cratageus monogyna Jacq. and Cratageus laevigata (Poiret D.C.) dependent on vegetation|lang=French|journal=Plantes Medicinales: Phytotherapie|year= 1991|volume =25| pages= 12–16}}{{Cite journal |last=Khokhlova |first=Kateryna |last2=Zdoryk |first2=Oleksandr |last3=Vyshnevska |first3=Liliia |date=January 2020 |title=Chromatographic characterization on flavonoids and triterpenes of leaves and flowers of 15 crataegus L. species |url=https://pubmed.ncbi.nlm.nih.gov/30417671/ |journal=Natural Product Research |volume=34 |issue=2 |pages=317–322 |doi=10.1080/14786419.2018.1528589 |issn=1478-6427 |pmid=30417671}}

Immobilized Candida antarctica lipase can be used to catalyze the regioselective acylation of flavonoids.{{cite journal | vauthors = Passicos E, Santarelli X, Coulon D | title = Regioselective acylation of flavonoids catalyzed by immobilized Candida antarctica lipase under reduced pressure | journal = Biotechnology Letters | volume = 26 | issue = 13 | pages = 1073–1076 | date = July 2004 | pmid = 15218382 | doi = 10.1023/B:BILE.0000032967.23282.15 | s2cid = 26716150 }}

• Phytochemical
• List of antioxidants in food
• List of phytochemicals in food
• Phytochemistry
• Secondary metabolites
• Homoisoflavonoids, related chemicals with a 16 carbons skeleton

{{Reflist}}

{{refbegin}}

• {{cite book | vauthors = Andersen ØM, Markham KR |title=Flavonoids: Chemistry, Biochemistry and Applications |date=2006 |publisher=CRC Press, Taylor & Francis |location=Boca Raton, FL |isbn=978-0-8493-2021-7}}
• {{cite book | vauthors = Grotewold E |title=The science of flavonoids |date=2006 |publisher=Springer |location=New York |isbn = 978-0-387-74550-3 }}
• {{cite book | title = Comparative Biochemistry of the Flavonoids | vauthors = Harborne JB | date = 1967 | url = https://books.google.com/books?id=CyTf2oObc7cC }}
• {{cite journal | doi = 10.1016/0022-2860(71)87109-0 | volume=10 | title=The systematic identification of flavonoids | year=1971 | journal=Journal of Molecular Structure | page=320| vauthors=Mabry TJ, Markham KR, Thomas MB | issue=2 }}

{{refend}}

{{Commons category|Flavonoids}}

• [http://www.ars.usda.gov/Services/docs.htm?docid=6231 USDA Database for the Flavonoid Content of Selected Foods, Release 3.1 (December 2013); data for 506 foods in the 5 subclasses of flavonoids provided in a separate PDF updated May 2014]
• [http://bioinfo.net.in/flavodb/home.html FlavoDB, Bioinformatics Centre, India, November 2019]

{{Flavonoids}}

{{Phenylpropanoids}}

{{Polyphenol}}

{{Authority control}}

Category:Nutrients

Category:Nutrition

Category:Flavonoid antioxidants

Category:Wood extracts