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40-504: Polyphenols ( / ˌ p ɒ l i ˈ f iː n oʊ l , - n ɒ l / ) are a large family of naturally occurring phenols . They are abundant in plants and structurally diverse. Polyphenols include phenolic acids , flavonoids , tannic acid , and ellagitannin , some of which have been used historically as dyes and for tanning garments . The name derives from the Ancient Greek word πολύς ( polus , meaning "many, much") and

80-678: A large, diverse group of compounds, making it difficult to determine their biological effects. They are not considered nutrients , as they are not used for growth, survival or reproduction, nor do they provide dietary energy . Therefore, they do not have recommended daily intake levels , as exist for vitamins , minerals , and fiber . In the United States, the Food and Drug Administration issued guidance to manufacturers that polyphenols cannot be mentioned on food labels as antioxidant nutrients unless physiological evidence exists to verify such

120-547: A molecule at the core of naturally occurring phenolic compounds of varying sizes, is itself not a polyphenol by the WBSSH definition, but is by the Quideau definition. The raspberry ellagitannin , on the other hand, with its 14 gallic acid moieties (most in ellagic acid-type components), and more than 40 phenolic hydroxyl groups, meets the criteria of both definitions of a polyphenol. Other examples of compounds that fall under both

160-571: A qualification and a Dietary Reference Intake value has been established – characteristics which have not been determined for polyphenols. In the European Union , two health claims were authorized between 2012 and 2015: 1) flavanols in cocoa solids at doses exceeding 200 mg per day may contribute to maintenance of vascular elasticity and normal blood flow; 2) olive oil polyphenols (5 mg of hydroxytyrosol and its derivatives (e.g. oleuropein complex and tyrosol ) may "contribute to

200-642: A role in epicuticle hardening ( sclerotization ). The hardening of the cuticle is due to the presence of a polyphenol oxidase . In crustaceans, there is a second oxidase activity leading to cuticle pigmentation . There is apparently no polyphenol tanning occurring in arachnids cuticle. Polyphenols are thought to play diverse roles in the ecology of plants. These functions include: Flax and Myriophyllum spicatum (a submerged aquatic plant) secrete polyphenols that are involved in allelopathic interactions. Polyphenols incorporate smaller parts and building blocks from simpler natural phenols , which originate from

240-571: A solvent like water, 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, critical carbon dioxide , high-pressure liquid extraction or use of ethanol in an immersion extractor. The extraction conditions (temperature, extraction time, ratio of solvent to raw material, particle size of

280-418: Is 2,6-ditert-butylphenol , a versatile antioxidant . Phenols undergo esterification . Phenol esters are active esters , being prone to hydrolysis. Phenols are reactive species toward oxidation . Oxidative cleavage, for instance cleavage of 1,2-dihydroxybenzene to the monomethylester of 2,4 hexadienedioic acid with oxygen, copper chloride in pyridine Oxidative de-aromatization to quinones also known as

320-418: Is a separation process consisting of the separation of a substance from a matrix . The distribution of a solute between two phases is an equilibrium condition described by partition theory. This is based on exactly how the analyte moves from the initial solvent into the extracting solvent. The term washing may also be used to refer to an extraction in which impurities are extracted from the solvent containing

360-473: Is a lack of commercially available standards for all polyphenolic molecules. Some polyphenols are traditionally used as dyes in leather tanning . For instance, in the Indian subcontinent , pomegranate peel , high in tannins and other polyphenols, or its juice, is employed in the dyeing of non-synthetic fabrics. Of some interest in the era of silver-based photography, pyrogallol and pyrocatechin are among

400-620: Is associated with a lower risk of mortality from gastric, colorectal, breast and lung cancers. The study found that an increase in isoflavone consumption by 10 mg per day was associated with a 7% decrease in risk from all cancers, and an increase in consumption of soy protein by 5 grams per day produced a 12% reduction in breast cancer risk. Polyphenols are under preliminary research for possible cognitive effects in healthy adults. Phenols Phenols are both synthesized industrially and produced by plants and microorganisms. Phenols are more acidic than typical alcohols. The acidity of

440-503: Is based on the number of carbons and was devised by Jeffrey Harborne and Simmonds in 1964 and published in 1980: More than 371 drugs approved by the FDA between the years of 1951 and 2020 contain either a phenol or a phenolic ether (a phenol with an alkyl), with nearly every class of small molecule drugs being represented, and natural products making up a large portion of this list. Extraction (chemistry) Extraction in chemistry

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480-405: Is the production of bisphenol A , which is produced by the condensation with acetone . Phenol is readily alkylated at the ortho positions using alkenes in the presence of a Lewis acid such as aluminium phenoxide : More than 100,000 tons of tert-butyl phenols are produced annually (year: 2000) in this way, using isobutylene (CH 2 =CMe 2 ) as the alkylating agent. Especially important

520-1049: Is the rapid polymerisation of o-quinones to produce black, brown or red polyphenolic pigments that causes fruit browning . In insects, PPO is involved in cuticle hardening. Polyphenols comprise up to 0.2–0.3% fresh weight for many fruits. Consuming common servings of wine, chocolate, legumes or tea may also contribute to about one gram of intake per day. According to a 2005 review on polyphenols: The most important food sources are commodities widely consumed in large quantities such as fruit and vegetables, green tea, black tea, red wine, coffee, chocolate, olives, and extra virgin olive oil. Herbs and spices, nuts and algae are also potentially significant for supplying certain polyphenols. Some polyphenols are specific to particular food (flavanones in citrus fruit, isoflavones in soya, phloridzin in apples); whereas others, such as quercetin, are found in all plant products such as fruit, vegetables, cereals, leguminous plants, tea, and wine. Some polyphenols are considered antinutrients – compounds that interfere with

560-514: 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 by high performance liquid chromatography (HPLC), and especially by reversed-phase liquid chromatography (RPLC), can be coupled to mass spectrometry . Purified compounds can be identified by

600-536: The Bucherer carbazole synthesis . Many phenols of commercial interest are prepared by elaboration of phenol or cresols . They are typically produced by the alkylation of benzene / toluene with propylene to form cumene then O 2 is added with H 2 SO 4 to form phenol ( Hock process ). In addition to the reactions above, many other more specialized reactions produce phenols: There are various classification schemes. A commonly used scheme

640-463: The Hildebrand solubility parameter : ethyl acetate < acetone < ethanol < methanol < acetone:water (7:3) < ethanol:water (8:2) < methanol:water (8:2) < water Solid-liquid extractions at laboratory scales can use Soxhlet extractors . A solid sample containing the desired compound along with impurities is placed in the thimble. An extracting solvent is chosen in which

680-533: The Teuber reaction . and oxone . In reaction depicted below 3,4,5-trimethylphenol reacts with singlet oxygen generated from oxone / sodium carbonate in an acetonitrile /water mixture to a para-peroxyquinole. This hydroperoxide is reduced to the quinole with sodium thiosulfate . Phenols are oxidized to hydroquinones in the Elbs persulfate oxidation . Reaction of naphtols and hydrazines and sodium bisulfite in

720-474: The diphenylpicrylhydrazyl (DPPH), oxygen radical absorbance capacity (ORAC), ferric reducing ability of plasma (FRAP) assays or inhibition of copper-catalyzed in vitro human low-density lipoprotein oxidation. New methods including the use of biosensors can help monitor the content of polyphenols in food. Quantitation results produced by the mean of diode array detector –coupled HPLC are generally given as relative rather than absolute values as there

760-406: The phenylpropanoid pathway for the phenolic acids or the shikimic acid pathway for gallotannins and analogs. Flavonoids and caffeic acid derivatives are biosynthesized from phenylalanine and malonyl-CoA . Complex gallotannins develop through the in vitro oxidation of 1,2,3,4,6-pentagalloylglucose or dimerization processes resulting in hydrolyzable tannins. For anthocyanidins, precursors of

800-512: The 21st century of a possible effect on cardiovascular diseases. For most polyphenols, there is no evidence for an effect on cardiovascular regulation, although there are some reviews showing a minor effect of consuming polyphenols, such as chlorogenic acid or flavan-3-ols , on blood pressure. Higher intakes of soy isoflavones may be associated with reduced risks of breast cancer in postmenopausal women and prostate cancer in men. A 2019 systematic review found that intake of soy and soy isoflavones

840-613: The Porter's assay). Total phenols (or antioxidant effect) can be measured using the Folin–Ciocalteu reaction . Results are typically expressed as gallic acid equivalents. Polyphenols are seldom evaluated by antibody technologies. 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, thiols and vitamin C . During this reaction,

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880-533: The WBSSH and Quideau definitions include the black tea theaflavin-3-gallate shown below, and the hydrolyzable tannin, tannic acid . Polyphenols are reactive species toward oxidation , hence their description as antioxidants in vitro . Polyphenols, such as lignin, are larger molecules ( macromolecules ). Their upper molecular weight limit is about 800 daltons , which allows for the possibility to rapidly diffuse across cell membranes so that they can reach intracellular sites of action or remain as pigments once

920-452: The absorption of essential nutrients – especially iron and other metal ions, which may bind to digestive enzymes and other proteins, particularly in ruminants . In a comparison of cooking methods, phenolic and carotenoid levels in vegetables were retained better by steaming compared to frying . Polyphenols in wine, beer and various nonalcoholic juice beverages can be removed using finings , substances that are usually added at or near

960-467: 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

1000-921: The cell senesces . Hence, many larger polyphenols are biosynthesized in situ from smaller polyphenols to non-hydrolyzable tannins and remain undiscovered in the plant matrix. Most polyphenols contain repeating phenolic moieties of pyrocatechol, resorcinol, pyrogallol, and phloroglucinol connected by esters (hydrolyzable tannins) or more stable C-C bonds (nonhydrolyzable condensed tannins ). Proanthocyanidins are mostly polymeric units of catechin and epicatechin . Polyphenols often have functional groups beyond hydroxyl groups . Ether ester linkages are common, as are carboxylic acids . The analysis techniques are those of phytochemistry : extraction , isolation, structural elucidation , then quantification . Polyphenols readily react with metal ions to form coordination complexes , some of which form Metal-phenolic Networks . Extraction of polyphenols can be performed using

1040-413: The chemical structure allowing antioxidant activity in vivo; they may exert biological activity as signaling molecules . Some polyphenols are considered to be bioactive compounds for which development of dietary recommendations was under consideration in 2017. In the 1930s , polyphenols (then called vitamin P ) were considered as a factor in capillary permeability , followed by various studies through

1080-514: The completion of the processing of brewing. With respect to food and beverages, the cause of astringency is not fully understood, but it is measured chemically as the ability of a substance to precipitate proteins. Astringency increases and bitterness decrease with the mean degree of polymerization . For water-soluble polyphenols, molecular weights between 500 and 3000 were reported to be required for protein precipitation. However, smaller molecules might still have astringent qualities likely due to

1120-455: The condensed tannin biosynthesis, dihydroflavonol reductase and leucoanthocyanidin reductase (LAR) are crucial enzymes with subsequent addition of catechin and epicatechin moieties for larger, non-hydrolyzable tannins. The glycosylated form develops from glucosyltransferase activity and increases the solubility of polyphenols. Polyphenol oxidase (PPO) is an enzyme that catalyses the oxidation of o-diphenols to produce o-quinones . It

1160-559: The desired compound . Liquid-liquid extractions in the laboratory usually make use of a separatory funnel , where two immiscible phases are combined to separate a solute from one phase into the other, according to the relative solubility in each of the phases. Typically, this will be to extract organic compounds out of an aqueous phase and into an organic phase, but may also include extracting water-soluble impurities from an organic phase into an aqueous phase. Common extractants may be arranged in increasing order of polarity according to

1200-531: The epidermis, bark layers, flowers and fruits but also play important roles in the decomposition of forest litter, and nutrient cycles in forest ecology. Absolute concentrations of total phenols in plant tissues differ widely depending on the literature source, type of polyphenols and assay; they are in the range of 1–25% total natural phenols and polyphenols, calculated with reference to the dry green leaf mass. Polyphenols are also found in animals. In arthropods , such as insects, and crustaceans polyphenols play

1240-535: The fluorescence signal. 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. Some methods for quantification of total polyphenol content in vitro are based on colorimetric measurements. Some tests are relatively specific to polyphenols (for instance

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1280-434: The formation of unprecipitated complexes with proteins or cross-linking of proteins with simple phenols that have 1,2-dihydroxy or 1,2,3-trihydroxy groups. Flavonoid configurations can also cause significant differences in sensory properties, e.g. epicatechin is more bitter and astringent than its chiral isomer catechin . In contrast, hydroxycinnamic acids do not have astringent qualities, but are bitter. Polyphenols are

1320-651: The hydroxyl group in phenols is commonly intermediate between that of aliphatic alcohols and carboxylic acids (their pK a is usually between 10 and 12). Deprotonation of a phenol forms a corresponding negative phenolate ion or phenoxide ion , and the corresponding salts are called phenolates or phenoxides ( aryloxides according to the IUPAC Gold Book). Phenols are susceptible to Electrophilic aromatic substitutions . Condensation with formaldehyde gives resinous materials, famously Bakelite . Another industrial-scale electrophilic aromatic substitution

1360-424: The impurities are insoluble and the desired compound has at least limited solubility. The solvent is refluxed and condensed solvent falls into the thimble and dissolves the desired compound which then passes back through the filter into the flask. After extraction is complete the solvent can be removed and the desired product collected. Boiling tea leaves in water extracts the tannins, theobromine, and caffeine out of

1400-508: The means of nuclear magnetic resonance . 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 plant science , to enhance

1440-517: The oldest photographic developers . Natural polyphenols have long been proposed as renewable precursors to produce plastics or resins by polymerization with formaldehyde , as well as adhesives for particleboards. The aims are generally to make use of plant residues from grape, olive (called pomaces ), or pecan shells left after processing. The most abundant polyphenols are the condensed tannins , found in virtually all families of plants. Larger polyphenols are often concentrated in leaf tissue,

1480-494: The protection of blood lipids from oxidative damage", if consumed daily. As of 2022, clinical trials that assessed the effect of polyphenols on health biomarkers are limited, with results difficult to interpret due to the wide variation of intake values for both individual polyphenols and total polyphenols. Polyphenols were once considered as antioxidants , but this concept is obsolete. Most polyphenols are metabolized by catechol-O-methyltransferase , and therefore do not have

1520-549: The sample, solvent type, and solvent concentrations) for different raw materials and extraction methods have to be optimized. 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. Concentration can be made by ultrafiltration . Purification can be achieved by preparative chromatography . Phosphomolybdic acid

1560-437: The tannins). In terms of properties, the WBSSH describes the polyphenols as follows: In terms of structures, the WBSSH recognizes two structural family that have these properties: According to Stéphane Quideau, the term "polyphenol" refers to compounds derived from the shikimate / phenylpropanoid and/or the polyketide pathway, featuring more than one phenolic unit and deprived of nitrogen-based functions. Ellagic acid ,

1600-620: The word ‘phenol’ which refers to a chemical structure formed by attachment of an aromatic benzenoid ( phenyl ) ring to a hydroxyl (-OH) group (hence the -ol suffix). The term "polyphenol" has been in use at least since 1894. The term polyphenol is not well-defined, but it is generally agreed that they are natural products with "several hydroxyl groups on aromatic rings " including four principal classes: "phenolic acids, flavonoids, stilbenes, and lignans". The White–Bate-Smith–Swain–Haslam (WBSSH) definition characterized structural characteristics common to plant phenolics used in tanning (i.e.,

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