tannins

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A bottle of tannic acid.
Tannins are astringent, bitter-tasting plant polyphenols that bind and precipitate proteins. The term tannin refers to the use of tannins in tanning animal hides into leather; however, the term is widely applied to any large polyphenolic compound containing sufficient hydroxyls and other suitable groups (such as carboxyls) to form strong complexes with proteins and other macromolecules. Tannins have molecular weights ranging from 500 to over 3,000.[1]

Base Unit:
Gallic Acid

Flavone
Class/Polymer:Hydrolyzable TanninsCondensed Tannins


Tannins are usually divided into hydrolyzable tannins and condensed tannins (proanthocyanidins).

Hydrolyzable Tannins

At the center of a hydrolyzable tannin molecule, there is a polyol carbohydrate (usually D-glucose). The hydroxyl groups of the carbohydrate are partially or totally esterified with phenolic groups such as gallic acid (in gallotannins) or ellagic acid (in ellagitannins). Hydrolyzable tannins are hydrolyzed by weak acids or weak bases to produce carbohydrate and phenolic acids.

Examples of gallotannins are the gallic acid esters of glucose in tannic acid (C76H52O46), found in the leaves and bark of many plant species.

Condensed Tannins

Condensed tannins, also known as proanthocyanidins, are polymers of 2 to 50 (or more) flavonoid units that are joined by carbon-carbon bonds, which are not susceptible to being cleaved by hydrolysis. While hydrolyzable tannins and most condensed tannins are water soluble, some very large condensed tannins are insoluble.

Foods with tannins

Tea

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Darjeeling tea infusion
The tea plant (Camellia sinensis) is an example of a plant said to have a naturally high tannin content. When any type of tea leaf is steeped in hot water it brews a "tart" (astringent) flavour that is characteristic of tannins. This is due to the catechins and other flavonoids. Tea "tannins" are chemically distinct from other types of plant tannins such as tannic acid[2] and tea extracts have been reported to contain no tannic acid[3].

Wine

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A glass of red wine
Tannins (mainly condensed tannins) are also found in wine, particularly red wine. Tannins in wine can come from many sources and the tactile properties differ depending on the source. Tannins in grape skins and seeds (the latter being especially harsh) tend to be more noticeable in red wines, which are fermented while in contact with the skins and seeds. Tannins extracted from grapes are condensed tannins, which are polymers of procyanidin monomers. Hydrolysable tannins are extracted from the oak wood the wine is aged in. Hydrolysable tannins are more easily oxidised than condensed tannins.

Modern winemakers take great care to minimize undesirable tannins from seeds by crushing grapes gently to extract their juice. Pressing the grapes results in press wine which is more tannic and might be kept separately. Wines can also take on tannins if matured in oak or wood casks with a high tannin content. Tannins play an important role in preventing oxidation in aging wine and appear to polymerize and make up a major portion of the sediment in wine.

Recently, a study in wine production and consumption has shown that tannins in the form of procyanidins, have a beneficial effect on vascular health. The study showed that tannins suppressed production of the peptide responsible for hardening arteries. To support their findings, the study also points out that wines from the regions of southwest France and Sardinia are particularly rich in procyanidins, and that these regions also produce populations with longer life spans.[4]

Fruits

Pomegranates

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Pomegranate fruit, opened
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Pomegranate seeds
Pomegranates contain a diverse array of tannins, particularly hydrolysable tannins. The most abundant of pomegranate tannins are called punicalagins. Punicalagins have a molecular weight of 1038 and are the largest molecule found intact in rat plasma after oral ingestion[5] and were found to show no toxic effects in rats who were given a 6% diet of punicalagins for 37 days.[6]. Punicalagins are also found to be the major component responsible for pomegranate juice's antioxidant and health benefits [7]

Several dietary supplements and nutritional ingredients are available that contain extracts of whole pomegranate and/or are standardized to punicalagins, the marker compound of pomegranate. Extracts of pomegranate are also Generally Recognized as Safe (GRAS) by the United States Food and Drug Administration. It has been recommended to look for pomegranate ingredients that mimic the polyphenol ratio of the fruit, as potent synergistic effects have been observed in 'natural spectrum' extracts, especially pomegranate concentrate normalized to punicalagins.[8]

Persimmons

Some persimmons are highly astringent and therefore inedible when they are not extremely ripe (specifically the Korean, American, and Hachiya or Japanese). This is due to the high level of tannins, and if eaten by humans (and many other animals), the mouth will become completely dry, yet the saliva glands will continue to secrete saliva which cannot affect the tannin-laced food. Areca Catechu also contains tannin which contributes to its antibacterial properties

Berries

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Strawberries in a bowl
Most berries, such as cranberries[9] strawberries and blueberries,[10] contain both hydrolyzable and condensed tannins.

Nutrition

If ingested in excessive quantities, tannins inhibit the absorption of minerals such as iron into the body. This is because tannins are metal ion chelators, and tannin-chelated metal ions are not bioavailable. This may not be bad for someone with an infection, as iron is mopped up by the immune system to keep microorganisms from properly multiplying. Tannins have been shown to precipitate proteins,<ref name="Bate-Smith" /> which inhibits in some ruminant animals the absorption of nutrients from high-tannin grains such as sorghum.

Uses

Tannins are an important ingredient in the process of tanning leather. Oak bark has traditionally been the primary source of tannery tannin, though inorganic tanning agents are also in use today.

Tannins may be employed medicinally in antidiarrheal, hemostatic, and antihemorrhoidal compounds.

Tannins produce different colors with ferric chloride (either blue, blue black, or green to greenish black) according to the type of tannin. Iron gall ink is produced by treating a solution of tannins with iron(II) sulfate.

Tannin is a component in a type of industrial particleboard adhesive developed jointly by the Tanzania Industrial Research and Development Organization and Forintek Labs Canada.

Potential Medical

Tannins, including gallo and ellagic acid (epigallitannins), are inhibitors of HIV replication.
  • 1,3,4-Tri-O-galloylquinic acid
  • 3,5-di-O-galloyl-shikimic acid,
  • 3,4,5-tri-O-galloylshikimic acid
  • punicalin
  • punicalagin
inhibited HIV replication in infected H9 lymphocytes with little cytotoxicity. Two compounds, punicalin and punicacortein C, inhibited purified HIV reverse transcriptase.[11]

References

Notes

1. ^ Bate-Smith and Swain, 1962, Flavonoid compounds. In : Comparative biochemistry. Florkin M. Mason H.S. Eds. Vol III. 75-809. Academic Press, New-York.
2. ^ Hamilton-Miller JM. Antimicrobial properties of tea (Camellia sinensis L.). Antimicrob Agents Chemother. 39(11): 2375-2377 (1995) PMID 8585711
3. ^ Wheeler, S.R. Tea and Tannins Science 204: 6-8 (1979) [1] as cited in Yam TS, Hamilton-Miller JM, Shah S. The effect of a component of tea (Camellia sinensis) on methicillin resistance, PBP2' synthesis, and beta-lactamase production in Staphylococcus aureus. J Antimicrob Chemother. 42(2):211-216. (1998) PMID 9738838
4. ^ R. Corder, W. Mullen, N. Q. Khan, S. C. Marks, E. G. Wood, M. J. Carrier and A. Crozier Nature 444, 566 (30 November 2006)
5. ^ Biomed. Pharmacother. 2002, 56, 276-82
6. ^ J. Agric. Food Chem. 2003, 51, 3493-3501
7. ^ J Agric Food Chem 2000 48 (10) 4581-89
8. ^ J Nutr Biochemistry 2005 (16) 360-367
9. ^ Vattem, D. A. Ghaedian, R. Shetty, K. Enhancing health benefits of berries through phenolic antioxidant enrichment: focus on cranberry Asia Pacific Journal of Clinical Nutrition (2005) 14(2) 120-130 [2]
10. ^ R. Puupponen-Pimiä, L. Nohynek, C. Meier, M. Kähkönen, M. Heinonen, A. Hopia & K.-M. Oksman-Caldentey, Antimicrobial properties of phenolic compounds from berries, Journal of Applied Microbiology 90(4) pp494 (2001) [3]
11. ^ [4]

General References

  • L. Calvi, G.C.J. Mwalongo, B.A. Mwingira, B. Riedl and J.A. Shields; Characterization of Wattle-Tannin-Based Adhesives for Tanzania (A paper published in Holzforchung Vol 49 No 2, 1995).

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An astringent substance is a chemical substance that tends to shrink or constrict body tissues, usually locally after topical medicinal application. The word "astringent" derives from Latin astringere, meaning "to bind fast".
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Polyphenols are a group of chemical substances found in plants, characterized by the presence of more than one phenol group per molecule. Polyphenols are generally further subdivided into hydrolyzable tannins, which are gallic acid esters of glucose and other sugars; and
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Precipitation is the formation of a solid in a solution during a chemical reaction. When the chemical reaction occurs the solid formed is called the precipitate. This can occur when an insoluble substance, the precipitate
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Proteins are large organic compounds made of amino acids arranged in a linear chain and joined together by peptide bonds between the carboxyl and amino groups of adjacent amino acid residues.
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Tanning is the process of converting putrescible skin into non-putrescible leather, usually with tannin, an acidic chemical compound that prevents decomposition and often imparts color.
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Hides are skins obtained from animals for human use. Examples of animal hide sources are deer and cattle typically used for producing leather, alligator skins, snake skins for shoes and fashion accessories and wild cats, minks and bears, whose skins are primarily sought for their
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Leather is a material created through the tanning of hides and skins of animals, primarily cattlehide. The tanning process converts the putrescible skin into a durable, long-lasting and versatile natural material for various uses.
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Hydroxyl in chemistry stands for a molecule consisting of an oxygen atom and a hydrogen atom connected by a covalent bond. The neutral form is a hydroxyl radical and the hydroxyl anion is called a hydroxide.
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Carboxyl group or carboxy group -COOH or CO2H is a functional group present in amino acids and carboxylic acids. Its structure composed of one carbon atom attached to an oxygen atom by double bond and to a hydroxyl group by a single bond.
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macromolecule implies large molecule. In the context of science and engineering, the term may be applied to conventional polymers and biopolymers (such as DNA) as well as non-polymeric molecules with large molecular mass such as lipids or macrocycles.
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molecular mass (abbreviated Mr) of a substance, formerly also called molecular weight and abbreviated as MW, is the mass of one molecule of that substance, relative to the unified atomic mass unit u (equal to 1/12 the mass of one atom of carbon-12).
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Gallic acid is an organic acid, also known as 3,4,5-trihydroxybenzoic acid, found in gallnuts, sumac, witch hazel, tea leaves, oak bark, and other plants. The chemical formula is C6H2(OH)3CO2H.
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Flavones are a class of flavonoids based on the backbone of 2-phenylchromen-4-one (2-phenyl-1-benzopyran-4-one) shown on the right.

Natural flavones include Apigenin (4',5,7-trihydroxyflavone, Luteolin (3',4',5,7-tetrahydroxyflavone) and Tangeritin
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:Not to be confused with electrolysis


Hydrolysis is a chemical reaction or process in which a chemical compound is broken down by reaction with water.[1][2] This is the type of reaction that is used to break down polymers.
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Proanthocyanidin (also known as oligomeric proanthocyanidin (OPC), pycnogenol, leukocyanidin and leucoanthocyanin) is a class of flavonoids. It was discovered in 1936 by Professor Jacques Masquelier and called Vitamin P, although this name did not gain
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molecule is defined as a sufficiently stable electrically neutral group of at least two atoms in a definite arrangement held together by strong chemical bonds.[1][2] In organic chemistry and biochemistry, the term molecule
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Glucose (Glc), a monosaccharide (or simple sugar), is an important carbohydrate in biology. The living cell uses it as a source of energy and metabolic intermediate.
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Esterification is the general name for a chemical reaction in which two chemicals (typically an alcohol and an acid) form an ester as the reaction product. Esters are common in organic chemistry and biological materials, and often have a characteristic pleasant, fruity odor.
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Gallic acid is an organic acid, also known as 3,4,5-trihydroxybenzoic acid, found in gallnuts, sumac, witch hazel, tea leaves, oak bark, and other plants. The chemical formula is C6H2(OH)3CO2H.
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Ellagic acid is a polyphenol antioxidant found in numerous fruits and vegetables including raspberries, strawberries, cranberries, walnuts, pecans, pomegranates and other plant foods.
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Gallic acid is an organic acid, also known as 3,4,5-trihydroxybenzoic acid, found in gallnuts, sumac, witch hazel, tea leaves, oak bark, and other plants. The chemical formula is C6H2(OH)3CO2H.
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Esters are a class of chemical compounds and functional groups. Esters consist of an inorganic or organic acid in which at least one -OH (hydroxy) group is replaced by an -O-alkyl (alkoxy) group.
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Glucose (Glc), a monosaccharide (or simple sugar), is an important carbohydrate in biology. The living cell uses it as a source of energy and metabolic intermediate.
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Tannic acid, a commercial form of tannin, is a polyphenol. Its weak acidity (pKa around 10) is due to these phenol groups in the structure. Tannic acid is a basic ingredient in the chemical staining of wood.
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leaf is an above-ground plant organ specialized for photosynthesis. For this purpose, a leaf is typically flat (laminar) and thin, to expose the cells containing chloroplast (chlorenchyma tissue, a type of parenchyma) to light over a broad area, and to allow light to penetrate
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BARK (Binär Aritmetisk Relä-Kalkylator, Swedish for "Binary Arithmetic Relay Calculator") was completed in February 1950 at a cost of 400.000 Swedish kronor. BARK was a 32-bit machine and could perform addition in 150 ms and multiplication in 250 ms.
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Plantae
Haeckel, 1866[1]

Divisions

Green algae
  • Chlorophyta
  • Charophyta
Land plants (embryophytes)
  • Non-vascular land plants (bryophytes)

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Proanthocyanidin (also known as oligomeric proanthocyanidin (OPC), pycnogenol, leukocyanidin and leucoanthocyanin) is a class of flavonoids. It was discovered in 1936 by Professor Jacques Masquelier and called Vitamin P, although this name did not gain
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flavonoid refers to a class of plant secondary metabolites. According to the IUPAC nomenclature,[1] they can be classified into:
  • flavonoids, derived from 2-phenylchromen-4-one (2-phenyl-1,4-benzopyrone) structure
  • isoflavonoids

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:Not to be confused with electrolysis


Hydrolysis is a chemical reaction or process in which a chemical compound is broken down by reaction with water.[1][2] This is the type of reaction that is used to break down polymers.
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