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al plant foods and in dietary supplements flavonoids are not considered to be nutrients or biological antioxidants essential to body functions and have no established effects on human health or prevention of diseases 1 2 3 chemically flavonoids have the general structure of a 15 carbon skeleton consisting of two phenyl rings a and b and a heterocyclic ring c the ring containing the embedded oxygen 1 4 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 phenyl chromen 4 one 3 phenyl 1 4 benzopyrone structure and neoflavonoids derived from 4 phenyl coumarin 4 phenyl 1 2 benzopyrone structure 5 as ketone containing compounds the three flavonoid classes are grouped as anthoxanthins flavones and flavonols 1 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 4 history edit 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 later shown not to fulfil the criteria of a vitamin 6 so that the term vitamin p is now obsolete 7 molecular structure of the flavone backbone 2 phenyl 1 4 benzopyrone isoflavan structure neoflavonoids structure biosynthesis edit main article 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 1 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 1 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 1 a biochemical diagram showing the class of flavonoids and their source in nature through various inter related plant species functions in plants edit numbering some 5 000 individual compounds flavonoids are widely distributed in plants fulfilling numerous functions including attraction of pollinating insects deterrence of environmental stresses and regulation of cell growth 1 they are the most important plant pigments for flower coloration producing yellow red or blue pigmentation in petals evolved to attract pollinators 1 in higher plants they are involved in antioxidant roles in plant cells filtration of ultraviolet light symbiotic nitrogen fixation and defense against pathogens and pests they also act as plant chemical messengers physiological regulators and cell cycle inhibitors 1 2 flavonoids secreted by the root of their host plant help rhizobia in the infection stage of their symbiotic relationship with legumes such as 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 8 subgroups edit flavonoids have been classified according to their chemical structure and are usually subdivided into the following subgroups 1 9 anthocyanidins edit flavylium skeleton of anthocyanidins anthocyanidins are the aglycones of anthocyanins they use the flavylium 2 phenylchromenylium ion skeleton 1 examples cyanidin delphinidin malvidin pelargonidin peonidin petunidin anthoxanthins edit anthoxanthins are divided into two groups 10 group skeleton examples description functional groups structural formula 3 hydroxyl 2 3 dihydro flav one 2 phenylchromen 4 one luteolin apigenin tangeritin flav on ol or 3 hydroxy flav one 3 hydroxy 2 phenylchromen 4 one quercetin kaempferol myricetin fisetin galangin isorhamnetin pachypodol rhamnazin pyranoflavonols furanoflavonols flavanones edit flavanones group skeleton examples description functional groups structural formula 3 hydroxyl 2 3 dihydro flav an one 2 3 dihydro 2 phenylchromen 4 one hesperetin naringenin eriodictyol homoeriodictyol flavanonols edit flavanonols group skeleton examples description functional groups structural formula 3 hydroxyl 2 3 dihydro flav an on ol or 3 hydroxy flav an one or 2 3 dihydro flav on ol 3 hydroxy 2 3 dihydro 2 phenylchromen 4 one taxifolin or dihydroquercetin dihydrokaempferol flavans edit flavan structure include flavan 3 ols flavanols flavan 4 ols and flavan 3 4 diols skeleton name flavan 3 ol flavanol flavan 4 ol flavan 3 4 diol leucoanthocyanidin flavan 3 ols flavanols flavan 3 ols use the 2 phenyl 3 4 dihydro 2 h 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 edit 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 dietary sources edit parsley is a source of flavones blueberries are a source of dietary anthocyanins flavonoids are found in citrus 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 1 2 11 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 1 2 3 foods with a high flavonoid content include blackberries black currants parsley onions blueberries and strawberries red cabbage black tea dark chocolate and citrus fruits 1 2 12 one study found high flavonoid content in buckwheat 13 citrus flavonoids include hesperidin a glycoside of the flavanone hesperetin quercitrin rutin two glycosides of quercetin and the flavone tangeritin 1 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 14 peanut red skin contains significant polyphenol content including flavonoids 15 16 dietary intake edit adult flavonoid intake mg per day in europe pie charts indicate the relative consumption of different flavonoid compounds 17 food composition data for flavonoids were provided by the usda database on flavonoids 12 in the united states nhanes survey mean flavonoid intake was 190 mg per day in adults with flavan 3 ols as the main contributor 18 in the european union based on data from the european food safety authority efsa mean flavonoid intake was 140 mg d although there were considerable differences among individual countries 17 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 1 17 18 data are based on mean flavonoid intake of all countries included in the 2011 efsa comprehensive european food consumption database 17 non nutrient status in humans edit flavonoids are not considered as nutrients because there is no evidence for a cause and effect on specific cells or organs in vivo 1 2 3 the european food safety authority determined that dietary flavonoids do not have the characteristics of nutrients as they do not reduce disease risk affect physiological or behavioral functions improve satiety contribute calories or influence the growth and development of children 3 the bioavailability of flavonoids is low because they are extensively metabolized in the stomach small intestine and liver and are rapidly excreted 1 2 in the united states flavonoids and other polyphenols are not included on the fda list of nutrients 19 metabolism and excretion edit flavonoids are poorly absorbed in the human body less than 5 then are quickly metabolized into smaller fragments with unknown properties and rapidly excreted 1 2 20 21 22 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 1 2 3 microbial metabolism is a major contributor to the overall metabolism of dietary flavonoids 1 2 23 safety edit likely due to the low bioavailability and rapid metabolism and excretion of flavonoids there are no safety concerns and no adverse effects associated with high dietary intakes of flavonoids from plant foods 1 regulatory status edit due to the absence of proof for flavonoid health effects in clinical research neither the united states fda nor the european food safety authority has approved any flavonoids as prescription drugs 1 20 24 25 the 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 26 27 from 2020 to 2023 the fda issued 11 warning letters to american manufacturers of flavonoid dietary supplements for false advertising of health claims and illegal misbranding of products 28 research edit antioxidant research edit although flavonoids inhibit free radical activity in vitro high dietary intakes in humans would be 100 to 1 000 times less than circulating concentrations of dietary and endogenous antioxidants such as vitamin c glutathione and uric acid 1 2 further after digestion and metabolism in the body flavonoid derivatives would have lower antioxidant activity than the parent flavonoid rendering the smaller flavonoid metabolite with negligible antioxidant function 1 2 3 clinical research edit although numerous preliminary clinical studies have been conducted to assess the potential for dietary flavonoid intake to affect disease risk research has been inconclusive due to limitations of experimental design and absence of cause and effect evidence 1 2 3 inflammation edit inflammation has been implicated as a possible origin of numerous local and systemic diseases such as cancer 29 cardiovascular disorders 30 diabetes mellitus 31 and celiac disease 32 there is no clinical evidence that dietary flavonoids affect any of these diseases 1 cancer edit 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 1 33 there is little evidence to indicate that dietary flavonoids affect human cancer risk in general 1 cardiovascular diseases edit 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 1 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 1 34 in 2013 the efsa decided to permit health claims that 200 mg day of cocoa flavanols help s maintain the elasticity of blood vessels 35 36 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 37 38 synthesis detection quantification and semi synthetic alterations edit color spectrum edit 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 39 availability through microorganisms edit research has shown production of flavonoid molecules from genetically engineered microorganisms 40 41 tests for detection edit shinoda test edit 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 42 colours varying from orange to red indicated flavones red to crimson indicated flavonoids crimson to magenta indicated flavonones sodium hydroxide test edit 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 43 p dimethylaminocinnamaldehyde test edit 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 44 quantification edit lamaison and carnet have designed a test for the determination of the total flavonoid content of a sample alci 3 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...
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