Flavonoids (or bioflavonoids) (from the Latin word flavus meaning yellow, their color in nature) are a class of plant secondary metabolites. Flavonoids were referred to as Vitamin P  (probably because of the effect they had on the permeability of vascular capillaries) from the mid-1930s to early 50s, but the term has since fallen out of use.
Chemically, they have the general structure of a 15-carbon skeleton, which consists of two phenyl rings (A and B) and heterocyclic ring (C). This carbon structure can be abbreviated C6-C3-C6. According to the IUPAC nomenclature, they can be classified into:
- flavonoids or bioflavonoids
- isoflavonoids, derived from 3-phenylchromen-4-one (3-phenyl-1,4-benzopyrone) structure
- neoflavonoids, derived from 4-phenylcoumarine (4-phenyl-1,2-benzopyrone) structure
The three flavonoid classes above are all ketone-containing compounds, and as such, are anthoxanthins (flavones and flavonols). This class was the first to be termed bioflavonoids. The terms flavonoid and bioflavonoid have also been more loosely used to describe non-ketone polyhydroxy polyphenol compounds which are more specifically termed flavanoids. The three cycle or heterocycles in the flavonoid backbone are generally called ring A, B and C. Ring A usually shows a phloroglucinol substitution pattern.
- 1 Biosynthesis
- 2 Functions of flavonoids in plants
- 3 Salutary effects on human health
- 4 Medical research
- 5 Dietary sources
- 6 Subgroups
- 7 Isoflavonoids
- 8 Synthesis, detection, quantification, and semi-synthetic alterations
- 9 See also
- 10 References
- 11 Further reading
- 12 External links
Functions of flavonoids in plants
Flavonoids are widely distributed in plants, fulfilling many functions. Flavonoids are the most important plant pigments for flower coloration, producing yellow or red/blue pigmentation in petals designed to attract pollinator animals. In higher plants, flavonoids 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.
Salutary effects on human health
Before any chemical compound can be approved as a pharmaceutical drug or any food can be labelled with a health claim, it must undergo extensive in vitro, in vivo, and clinical testing to confirm both safety and efficacy. National and international regulatory authorities like the US Food and Drug Administration (FDA) and European Food Safety Authority (EFSA) are responsible for assessing this evidence and granting such approval. At the current time, neither the FDA nor the EFSA has approved any health claim for flavonoids, or approved any flavonoids as pharmaceutical drugs. Moreover, several companies have been cautioned by the FDA over misleading health claims.
Flavonoids have been shown to have a wide range of biological and pharmacological activities in in vitro studies. Examples include anti-allergic, anti-inflammatory, antioxidant, anti-microbial (antibacterial, antifungal, and antiviral), anti-cancer, and anti-diarrheal activities. Flavonoids have also been shown to inhibit topoisomerase enzymes and to induce DNA mutations in the mixed-lineage leukemia (MLL) gene in in vitro studies. However, in most of the above cases no follow up in vivo or clinical research has been performed, leaving it impossible to say if these activities have any beneficial or detrimental effect on human health. Biological and pharmacological activities which have been investigated in greater depth are described below.
Flavonoid-rich grape-seed extract has been shown to have antioxidant activity in in vivo studies with rats, protecting their gastrointestinal mucosa against the reactive oxygen species generated by acute and chronic stress. In the absence of any additional in vivo data, it is impossible to say if these findings are generalizable to all flavonoids. Also, without any clinical studies, it is impossible to say if the antioxidant activity of grape-seed flavonoids offers any protection against oxidative stress in the human gastrointestinal tract.
Research at the Linus Pauling Institute and the European Food Safety Authority shows that flavonoids are poorly absorbed in the human body (less than 5%), with most of what is absorbed being quickly metabolized and excreted. These findings suggest that flavonoids have negligible systemic antioxidant activity, and that the increase in antioxidant capacity of blood seen after consumption of flavonoid-rich foods is not caused directly by flavonoids, but due to increased production of uric acid resulting from excretion of flavonoids from the body.
Preliminary studies indicate that flavonoids may affect anti-inflammatory mechanisms via their ability to inhibit reactive oxygen or nitrogen compounds. Flavonoids have also been proposed to inhibit the pro-inflammatory activity of enzymes involved in free radical production, such as cyclooxygenase, lipoxygenase or inducible nitric oxide synthase, and to modify intracellular signaling pathways in immune cells.
Procyanidins, a class of flavonoids, have been shown in preliminary research to have anti-inflammatory mechanisms including modulation of the arachidonic acid pathway, inhibition of gene transcription, protein expression and activity of inflammatory enzymes, as well as secretion of anti-inflammatory mediators.
Clinical studies investigating the relationship between flavonoid consumption and cancer prevention/development are conflicting for most types of cancer, probably because most studies are retrospective in design and use a small sample size. Two apparent exceptions are gastric carcinoma and smoking-related cancers. Dietary flavonoid intake is associated with reduced gastric carcinoma risk in women, and reduced aerodigestive tract cancer risk in smokers.
Among the most intensively studied of general human disorders possibly affected by dietary flavonoids, preliminary cardiovascular disease research has revealed the following mechanisms under investigation in patients or normal subjects:
- inhibit coagulation, thrombus formation or platelet aggregation
- reduce risk of atherosclerosis
- reduce arterial blood pressure and risk of hypertension
- reduce oxidative stress and related signaling pathways in blood vessel cells
- modify vascular inflammatory mechanisms
- improve endothelial and capillary function
- modify blood lipid levels
- regulate carbohydrate and glucose metabolism
- modify mechanisms of aging
Listed on the clinical trial registry of the US National Institutes of Health (November 2013) are 36 human studies completed or underway to study the dietary effects of plant flavonoids on cardiovascular diseases.
Flavonoids have been shown to have (a) direct antibacterial activity, (b) synergistic activity with antibiotics, and (c) the ability to suppress bacterial virulence factors in numerous in vitro and a limited number of in vivo studies. Noteworthy among the in vivo studies is the finding that oral quercetin protects guinea pigs against the Group 1 carcinogen Helicobacter pylori. Researchers from the European Prospective Investigation into Cancer and Nutrition have speculated this may be one reason why dietary flavonoid intake is associated with reduced gastric carcinoma risk in European women. Additional in vivo and clinical research is needed to determine if flavonoids could be used as pharmaceutical drugs for the treatment of bacterial infection, or whether dietary flavonoid intake offers any protection against infection.
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". 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 other berries, black tea, green tea and oolong tea, bananas, all citrus fruits, Ginkgo biloba, red wine, sea-buckthorns, and dark chocolate (with a cocoa content of 70% or greater). Further information on dietary sources of flavonoids can be obtained from the US Department of Agriculture flavonoid database.
Flavonoids exist naturally in cocoa, but because they can be bitter, they are often removed from chocolate, even dark chocolate. Although flavonoids are present in milk chocolate, milk may interfere with their absorption.
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 ):
|Description||Functional groups||Structural formula|
|Flavone||2-phenylchromen-4-one||✗||✗||Luteolin, Apigenin, Tangeritin|
|3-hydroxy-2-phenylchromen-4-one||✓||✗||Quercetin, Kaempferol, Myricetin, Fisetin, Galangin, Isorhamnetin, Pachypodol, Rhamnazin, Pyranoflavonols, Furanoflavonols,|
|Description||Functional groups||Structural formula|
|Flavanone||2,3-dihydro-2-phenylchromen-4-one||✗||✓||Hesperetin, Naringenin, Eriodictyol, Homoeriodictyol|
|Description||Functional groups||Structural formula|
|3-hydroxy-2,3-dihydro-2-phenylchromen-4-one||✓||✓||Taxifolin (or Dihydroquercetin), Dihydrokaempferol|
- 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 (Epicatechin (EC)), Epigallocatechin (EGC), Epicatechin 3-gallate (ECg), Epigallocatechin 3-gallate (EGCg)
- Isoflavones use the 3-phenylchromen-4-one skeleton (with no hydroxyl group substitution on carbon at position 2)
Synthesis, detection, quantification, and semi-synthetic alterations
Availability through microorganisms
Tests for detection
- Shinoda test
Four pieces of magnesium fillings (ribbon) are added to the ethanolic extract followed by few drops of concentrated hydrochloric acid. A pink or red colour indicates the presence of flavonoid. Colours varying from orange to red indicated flavones, red to crimson indicated flavonoids, crimson to magenta indicated flavonones.
- Sodium hydroxide test
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.
- p-Dimethylaminocinnamaldehyde test
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.
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 10 minutes at ambient temperature and the absorbance of the solution is read at 440 nm. Flavonoid content is expressed in mg/g of quercetin.
- List of antioxidants in food
- List of phytochemicals in food
- Secondary metabolites
- Homoisoflavonoids, related chemicals with a 16 carbons skeleton
- Benthsath, A.; Rusznyak, S. T.; Szent-Györgyi, A. (1937). "Vitamin P.". Nature 139: 326–327. doi:10.1038/139326b0.
- Mobh, Shiro (1938). "Research for Vitamin P". The Journal of Biochemistry 29 (3): 487–501.
- McNaught, Alan D; Wilkinson, Andrew; IUPAC (1997). "Flavonoids (isoflavonoids and neoflavonoids)". IUPAC Compendium of Chemical Terminology (2 ed.). Oxford: Blackwell Scientific. Archived from the original on 29 June 2011.
- flavonoids (isoflavonoids and neoflavonoids) IUPAC. Compendium of Chemical Terminology, 2nd ed. (the "Gold Book"). Compiled by A. D. McNaught and A. Wilkinson. Blackwell Scientific Publications, Oxford (1997). XML on-line corrected version: http://goldbook.iupac.org (2006–) created by M. Nic, J. Jirat, B. Kosata; updates compiled by A. Jenkins. ISBN 0-9678550-9-8. doi:10.1351/goldbook. Last update: 2012-08-19; version: 2.3.2. DOI of this term: doi:10.1351/goldbook.F02424. (Original PDF version: http://goldbook.iupac.org/goldbook/F02424.html. The PDF version is out of date and is provided for reference purposes only.) Retrieved 16 September 2012.
- Galeotti, F; Barile, E; Curir, P; Dolci, M; Lanzotti, V (2008). "Flavonoids from carnation (Dianthus caryophyllus) and their antifungal activity". Phytochemistry Letters 1: 44. doi:10.1016/j.phytol.2007.10.001.
- "FDA approved drug products". US Food and Drug Administration. Retrieved 8 November 2013.
- "Health Claims Meeting Significant Scientific Agreement". US Food and Drug Administration. Retrieved 8 November 2013.
- EFSA Panel on Dietetic Products, Nutrition and Allergies (NDA)2, 3 European Food Safety Authority (EFSA), Parma, Italy (2010). "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". EFSA Journal 8 (2): 1489. doi:10.2903/j.efsa.2010.1489.
- "Inspections, Compliance, Enforcement, and Criminal Investigations (Flavonoid Sciences)". US Food and Drug Administration. Retrieved 8 November 2013.
- "Inspections, Compliance, Enforcement, and Criminal Investigations (Unilever, Inc.)". US Food and Drug Administration. Retrieved 25 October 2013.
- "Lipton green tea is a drug". NutraIngredients-USA.com. Retrieved 25 October 2013.
- "Fruits Are Good for Your Health? Not So Fast: FDA Stops Companies From Making Health Claims About Foods". TheDailyGreen.com. Retrieved 25 October 2013.
- Yamamoto, Yumi; Gaynor, Richard B. (2001). "Therapeutic potential of inhibition of the NF-κB pathway in the treatment of inflammation and cancer". Journal of Clinical Investigation 107 (2): 135–42. doi:10.1172/JCI11914. PMC 199180. PMID 11160126.
- Cazarolli LH, Zanatta L, Alberton EH, Figueiredo MS, Folador P, Damazio RG, Pizzolatti MG, Silva FR (2008). "Flavonoids: Prospective Drug Candidates". Mini-Reviews in Medicinal Chemistry 8 (13): 1429–1440. doi:10.2174/138955708786369564. PMID 18991758.
- Cushnie TPT, Lamb AJ (2011). "Recent advances in understanding the antibacterial properties of flavonoids". International Journal of Antimicrobial Agents 38 (2): 99–107. doi:10.1016/j.ijantimicag.2011.02.014. PMID 21514796.
- Manner S, Skogman M, Goeres D, Vuorela P, Fallarero A (2013). "Systematic exploration of natural and synthetic flavonoids for the inhibition of Staphylococcus aureus biofilms". International Journal of Molecular Sciences 14 (10): 19434–19451. doi:10.3390/ijms141019434. PMC 3821565. PMID 24071942.
- Cushnie TPT, Lamb AJ (2005). "Antimicrobial activity of flavonoids". International Journal of Antimicrobial Agents 26 (5): 343–356. doi:10.1016/j.ijantimicag.2005.09.002. PMID 16323269.
- Friedman M (2007). "Overview of antibacterial, antitoxin, antiviral, and antifungal activities of tea flavonoids and teas". Molecular Nutrition and Food Research 51 (1): 116–134. doi:10.1002/mnfr.200600173. PMID 17195249.
- de Sousa RR, Queiroz KC, Souza AC, Gurgueira SA, Augusto AC, Miranda MA, Peppelenbosch MP, Ferreira CV, Aoyama H. (2007). "Phosphoprotein levels, MAPK activities and NFkappaB expression are affected by fisetin". J Enzyme Inhib Med Chem 22 (4): 439–444. doi:10.1080/14756360601162063. PMID 17847710.
- Schuier M, Sies H, Illek B, Fischer H (2005). "Cocoa-related flavonoids inhibit CFTR-mediated chloride transport across T84 human colon epithelia". J. Nutr. 135 (10): 2320–5. PMID 16177189.
- Esselen, Melanie; Fritz, Jessica; Hutter, Melanie; Marko, Doris (2009). "Delphinidin Modulates the DNA-Damaging Properties of Topoisomerase II Poisons". Chemical Research in Toxicology 22 (3): 554–64. doi:10.1021/tx800293v. PMID 19182879.
- Bandele, O.J.; Clawson, S.J.; Osheroff, N. (2008). "Dietary polyphenols as topoisomerase II poisons: B-ring substituents determine the mechanism of enzyme-mediated DNA cleavage enhancement". Chemical Research in Toxicology 21 (6): 1253–1260. doi:10.1021/tx8000785. PMC 2737509. PMID 18461976.
- Barjesteh van Waalwijk van Doorn-Khosrovani S, Janssen J, Maas LM, Godschalk RW, Nijhuis JG, van Schooten FJ (2007). "Dietary flavonoids induce MLL translocations in primary human CD34+ cells". Carcinogenesis 28 (8): 1703–9. doi:10.1093/carcin/bgm102. PMID 17468513.
- Bagchi, Manashi; Milnes, Mark; Williams, Casey; Balmoori, Jaya; Ye, Xumei; Stohs, Sidney; Bagchi, Debasis (1999). "Acute and chronic stress-induced oxidative gastrointestinal injury in rats, and the protective ability of a novel grape seed proanthocyanidin extract". Nutrition Research 19 (8): 1189–1199. doi:10.1016/S0271-5317(99)00080-9.
- Lotito SB, Frei B (2006). "Consumption of flavonoid-rich foods and increased plasma antioxidant capacity in humans: cause, consequence, or epiphenomenon?". Free Radic. Biol. Med. 41 (12): 1727–46. doi:10.1016/j.freeradbiomed.2006.04.033. PMID 17157175.
- Williams RJ, Spencer JP, Rice-Evans C (2004). "Flavonoids: antioxidants or signalling molecules?". Free Radical Biology & Medicine 36 (7): 838–49. doi:10.1016/j.freeradbiomed.2004.01.001. PMID 15019969.
- Stauth, David (5 March 2007) Studies force new view on biology of flavonoids, EurekAlert!. Adapted from a news release issued by Oregon State University
- Ravishankar, D.; Rajora, A. K.; Greco, F.; Osborn, H. M. I. (2013). "Flavonoids as prospective compounds for anti-cancer therapy". The International Journal of Biochemistry & Cell Biology 45 (12): 2821–2831. doi:10.1016/j.biocel.2013.10.004. PMID 24128857.
- Manach, C.; Mazur, A.; Scalbert, A. (2005). "Polyphenols and prevention of cardiovascular diseases". Current opinion in lipidology 16 (1): 77–84. doi:10.1097/00041433-200502000-00013. PMID 15650567.
- Babu, P. V. A.; Liu, D.; Gilbert, E. R. (2013). "Recent advances in understanding the anti-diabetic actions of dietary flavonoids". The Journal of Nutritional Biochemistry 24 (11): 1777–1789. doi:10.1016/j.jnutbio.2013.06.003. PMC 3821977. PMID 24029069.
- Ferretti, G.; Bacchetti, T.; Masciangelo, S.; Saturni, L. (2012). "Celiac Disease, Inflammation and Oxidative Damage: A Nutrigenetic Approach". Nutrients 4 (12): 243–257. doi:10.3390/nu4040243. PMC 3347005. PMID 22606367.
- Izzi, V.; Masuelli, L.; Tresoldi, I.; Sacchetti, P.; Modesti, A.; Galvano, F.; Bei, R. (2012). "The effects of dietary flavonoids on the regulation of redox inflammatory networks". Frontiers in bioscience (Landmark edition) 17 (7): 2396–2418. doi:10.2741/4061. PMID 22652788.
- Gomes, A.; Couto, D.; Alves, A.; Dias, I.; Freitas, M.; Porto, G. A.; Duarte, J. A.; Fernandes, E. (2012). "Trihydroxyflavones with antioxidant and anti-inflammatory efficacy". BioFactors 38 (5): 378–386. doi:10.1002/biof.1033. PMID 22806885.
- Martinez-Micaelo, N.; González-Abuín, N.; Ardèvol, A.; Pinent, M.; Blay, M. T. (2012). "Procyanidins and inflammation: Molecular targets and health implications". BioFactors 38 (4): 257–265. doi:10.1002/biof.1019. PMID 22505223.
- Romagnolo DF, Selmin OI (2012). "Flavonoids and cancer prevention: a review of the evidence". J Nutr Gerontol Geriatr 31 (3): 206–38. doi:10.1080/21551197.2012.702534. PMID 22888839.
- González CA, Sala N, Rokkas T (2013). "Gastric cancer: epidemiologic aspects". Helicobacter 18 (Supplement 1): 34–38. doi:10.1111/hel.12082. PMID 24011243.
- Woo HD, Kim J (2013). "Dietary flavonoid intake and smoking-related cancer risk: a meta-analysis". PLoS ONE 8 (9): e75604. doi:10.1371/journal.pone.0075604. PMID 24069431.
- Higdon, J; Drake, V; Frei, B (March 2009). "Non-Antioxidant Roles for Dietary Flavonoids: Reviewing the relevance to cancer and cardiovascular diseases". Nutraceuticals World. Rodman Media. Retrieved 24 November 2013.
- Van Dam, R. M.; Naidoo, N.; Landberg, R. (2013). "Dietary flavonoids and the development of type 2 diabetes and cardiovascular diseases". Current Opinion in Lipidology 24 (1): 25–33. doi:10.1097/MOL.0b013e32835bcdff. PMID 23254472.
- Tangney, C. C.; Rasmussen, H. E. (2013). "Polyphenols, Inflammation, and Cardiovascular Disease". Current Atherosclerosis Reports 15 (5): 324. doi:10.1007/s11883-013-0324-x. PMC 3651847. PMID 23512608.
- Siasos, G.; Tousoulis, D.; Tsigkou, V.; Kokkou, E.; Oikonomou, E.; Vavuranakis, M.; Basdra, E. K.; Papavassiliou, A. G.; Stefanadis, C. (2013). "Flavonoids in atherosclerosis: An overview of their mechanisms of action". Current medicinal chemistry 20 (21): 2641–2660. doi:10.2174/0929867311320210003. PMID 23627935.
- "Flavonoids in cardiovascular disease clinical trials". Clinicaltrials.gov. US National Institutes of Health. November 2013. Retrieved November 24, 2013.
- Taylor PW, Hamilton-Miller JMT, Stapleton PD (2005). "Antimicrobial properties of green tea catechins". Food Science and Technology Bulletin 2 (7): 71–81. doi:10.1616/1476-2137.14184 (inactive 22 April 2014). PMC 2763290. PMID 19844590.
- Choi O, Yahiro K, Morinaga N, Miyazaki M, Noda M (2007). "Inhibitory effects of various plant polyphenols on the toxicity of Staphylococcal alpha-toxin". Microbial Pathogenesis 432 (5–6): 215–224. doi:10.1016/j.micpath.2007.01.007. PMID 17391908.
- Oh DR, Kim JR, Kim YR (2010). "Genistein inhibits Vibrio vulnificus adhesion and cytotoxicity to HeLa cells". Archives of Pharmacal Research 33 (5): 787–792. doi:10.1007/s12272-010-0520-y. PMID 20512479.
- González-Segovia R, Quintanar JL, Salinas E, Ceballos-Salazar R, Aviles-Jiménez F, Torres-López J (2008). "Effect of the flavonoid quercetin on inflammation and lipid peroxidation induced by Helicobacter pylori in gastric mucosa of guinea pig". Journal of Gastroenterology 43 (6): 441–447. doi:10.1007/s00535-008-2184-7. PMID 18600388.
- Zamora-Ros R, Agudo A, Luján-Barroso L, Romieu I, Ferrari P, Knaze V, Bueno-de-Mesquita HB, Leenders M, Travis RC, Navarro C, Sánchez-Cantalejo E, Slimani N, Scalbert A, Fedirko V, Hjartåker A, Engeset D, Skeie G, Boeing H, Förster J, Li K, Teucher B, Agnoli C, Tumino R, Mattiello A, Saieva C, Johansson I, Stenling R, Redondo ML, Wallström P, Ericson U, Khaw KT, Mulligan AA, Trichopoulou A, Dilis V, Katsoulis M, Peeters PH, Igali L, Tjønneland A, Halkjær J, Touillaud M, Perquier F, Fagherazzi G, Amiano P, Ardanaz E, Bredsdorff L, Overvad K, Ricceri F, Riboli E, González CA (2012). "Dietary flavonoid and lignan intake and gastric adenocarcinoma risk in the European Prospective Investigation into Cancer and Nutrition (EPIC) study". American Journal of Clinical Nutrition 96 (6): 1398–1408. doi:10.3945/ajcn.112.037358. PMID 23076618.
- Spencer, Jeremy P. E. (2008). "Flavonoids: modulators of brain function?". British Journal of Nutrition 99: ES60–77. doi:10.1017/S0007114508965776. PMID 18503736.
- USDA’s Database on the Flavonoid Content
- The Lancet (2007). "The devil in the dark chocolate". Lancet 370 (9605): 2070. doi:10.1016/S0140-6736(07)61873-X. PMID 18156011.
- Serafini, Mauro; Bugianesi, Rossana; Maiani, Giuseppe; Valtuena, Silvia; De Santis, Simone; Crozier, Alan (2003). "Plasma antioxidants from chocolate". Nature 424 (6952): 1013. doi:10.1038/4241013a. PMID 12944955.
- Serafini, M., Crozier, A., Bugianesi, R., Maiani, G., Valtuena, S., and Santis, S.D. (2003). "Nutrition: milk and absorption of dietary flavanols". Nature 424 (6952): 1013. doi:10.1038/4241013a. PMID 12944955.
- Ververidis Filippos, F; Trantas Emmanouil; Douglas Carl; Vollmer Guenter; Kretzschmar Georg; Panopoulos Nickolas (October 2007). "Biotechnology of flavonoids and other phenylpropanoid-derived natural products. Part I: Chemical diversity, impacts on plant biology and human health". Biotechnology Journal 2 (10): 1214–34. doi:10.1002/biot.200700084. PMID 17935117.
- Isolation of a UDP-glucose: Flavonoid 5-O-glucosyltransferase gene and expression analysis of anthocyanin biosynthetic genes in herbaceous peony (Paeonia lactiflora Pall.). Da Qiu Zhao, Chen Xia Han, Jin Tao Ge and Jun Tao, Electronic Journal of Biotechnology, 15 November 2012, Volume 15, Number 6, doi:10.2225/vol15-issue6-fulltext-7
- Hwang EI, Kaneko M, Ohnishi Y, Horinouchi S (May 2003). "Production of plant-specific flavanones by Escherichia coli containing an artificial gene cluster". Appl. Environ. Microbiol. 69 (5): 2699–706. doi:10.1128/AEM.69.5.2699-2706.2003. PMC 154558. PMID 12732539.
- Trantas, E; Panopoulos, Nickolas; Ververidis, Filippos (2009). "Metabolic engineering of the complete pathway leading to heterologous biosynthesis of various flavonoids and stilbenoids in Saccharomyces cerevisiae". Metabolic Engineering 11 (6): 355–366. doi:10.1016/j.ymben.2009.07.004. PMID 19631278.
- Ververidis, F; Trantas, Emmanouil; Douglas, Carl; Vollmer, Guenter; Kretzschmar, Georg; Panopoulos, Nickolas (2007). "Biotechnology of flavonoids and other phenylpropanoid-derived natural products. Part II: Reconstruction of multienzyme pathways in plants and microbes". Biotechnology Journal 2 (10): 1235–49. doi:10.1002/biot.200700184. PMID 17935118.
- Yisa, Jonathan (2009). "Phytochemical Analysis and Antimicrobial Activity Of Scoparia Dulcis and Nymphaea Lotus". Australian Journal of Basic and Applied Sciences 3 (4): 3975–3979.
- Bello, Isaac A; Ndukwe, George I; Audu, Oladimeji T; Habila, James D (2011). "A bioactive flavonoid from Pavetta crassipes K. Schum". Organic and Medicinal Chemistry Letters 1 (1): 14. doi:10.1186/2191-2858-1-14. PMC 3305906. PMID 22373191.
- A new colourimetric assay for flavonoids in pilsner beers. Jan A. Delcour and Didier Janssens de Varebeke, Journal of the Institute of Brewing, January–February 1985, Volume 91, Issue 1, pages 37–40, doi:10.1002/j.2050-0416.1985.tb04303.x
- Lamaison, JL and Carnet, A (1991). "Teneurs en principaux flavonoides des fleurs de Cratageus monogyna Jacq et de Cratageus Laevigata (Poiret D.C) en Fonction de la vegetation". Plantes Medicinales Phytotherapie 25: 12–16.
- Regioselective acylation of flavonoids catalyzed by immobilized Candida antarctica lipase under reduced pressure. Passicos E, Santarelli X and Coulon D, Biotechnol Lett., July 2004, 26(13), pages 1073-1076, PubMed
- Andersen, Ø.M. / Markham, K.R. (2006). Flavonoids: Chemistry, Biochemistry and Applications. CRC Press. ISBN 978-0-8493-2021-7
- Grotewold, Erich (2007). The Science of Flavonoids. Springer. ISBN 978-0-387-74550-3
- Comparative Biochemistry of the Flavonoids, by J.B. Harborne, 1967 (Google Books)
- The systematic identification of flavonoids, by T.J. Mabry, K.R. Markham and M.B. Thomas, 1970, doi:10.1016/0022-2860(71)87109-0
- Flavonoids (chemistry)
- Micronutrient Information Center – Flavonoids
- Flavonoid Composition of Fruit Tissues of Citrus Species
- FlavonoidViewer.jp (Japanese, English), a database on flavonoids by Arita Group (Univ of Tokyo, RIKEN Plant Science Center, and Keio Univ), Nishioka Group (Kyoto and Keio Univ) and Kanaya Group (NAIST)
- USDA Database of Flavonoid content of food (pdf)