A hydrolysable tannin or pyrogallol-type tannin is a type of tannin that, on heating with hydrochloric or sulfuric acids, yields gallic or ellagic acids. [1]
At the center of a hydrolysable tannin molecule, there is a carbohydrate (usually D-glucose but also cyclitols like quinic or shikimic acids). 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. Hydrolysable tannins are mixtures of polygalloyl glucoses and/or poly-galloyl quinic acid derivatives containing in between 3 up to 12 gallic acid residues per molecule. [2]
Hydrolysable tannins are hydrolysed 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.
Hydrolysable tannins can be extracted from different vegetable plants, such as chestnut wood ( Castanea sativa ), oak wood ( Quercus robur , Quercus petraea and Quercus alba ), tara pods ( Caesalpinia spinosa ), gallnuts ( Quercus infectoria and Rhus semialata ), myrobalan ( Terminalia chebula ), sumac ( Rhus coriaria ) and Aleppo gallnuts ( Andricus kollari ). [3] [4]
This section contains instructions, advice, or how-to content .(June 2020) |
50 mg of sample tannin in 5 ml 2N H2SO4 are put into constricted test tubes and frozen. The tubes are vacuum-sealed and heated for 24 hours at 100 °C. The tubes are cooled, opened and the contents made up to 50 ml with water. Then 1.5 ml of freshly prepared 0.667% w/v rhodanine in methanol and 1 ml of sample are mixed. After exactly 5 min 1 ml of 0.5 N KOH solution is added. After 2.5 min the mixture is diluted to 25 ml with distilled water and 5–10 min later the absorbance at 520 nm is measured. The measured absorbance obeys the relationship:
A520= [0.13 × (mg of gallic acid) ] +0.03
Gallic acid is used as a standard and the data are based on experiments carried out in triplicate.
10 mg of samples tannin in 1 ml 2N H2SO4 are put into constricted test tubes and frozen. The tubes are vacuum-waled and heated for 24 hours at 100 °C. Tubes were cooled, opened and the filtered content made up to 10 ml with pyridine. Then 1.1 ml of pyridine and l ml of sample are mixed in a dry test tube. After adding 0.10 ml of concentrated HCl and mixing, the sample is brought to 30 °C. The sample is quickly mixed after 0.10 ml of 1% (w/v) NaNO2 in water and the absorbance 538 nm is immediately recorded. After a 36 min incubating period at 30 °C, the absorbance is again recorded. The difference between the initial absorbance and the absorbance at 36 min (D A538) is proportional to the ellagic acid concentration. The measured absorbance obeys the relationship:
A538 = [0.03 × (mg of ellagic acid)] – 0.04
Ellagic acid is used as a standard and the data were based on experiments carried out in triplicate.
4.8 g sample tannin in 9 ml water are refluxed in 4.2 ml 40% NaOH for 6h at pH 12 - 13. Neutralization to pH = 6.8 - 7 is performed with 62% H2SO4.
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. [5]
Hydrolysable tannins have shown also potential antibacterial effects against Helicobacter pylori . [6]
In the past few years, hydrolysable tannins have also been studied for their potential effects against cancer through different mechanisms. [7] [8]
Tannins are a class of astringent, polyphenolic biomolecules that bind to and precipitate proteins and various other organic compounds including amino acids and alkaloids.
Gallic acid (also known as 3,4,5-trihydroxybenzoic acid) is a trihydroxybenzoic acid with the formula C6H2(OH)3CO2H. It is classified as a phenolic acid. It is found in gallnuts, sumac, witch hazel, tea leaves, oak bark, and other plants. It is a white solid, although samples are typically brown owing to partial oxidation. Salts and esters of gallic acid are termed "gallates".
Polyphenols 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.
Tannic acid is a specific form of tannin, a type of polyphenol. Its weak acidity (pKa around 6) is due to the numerous phenol groups in the structure. The chemical formula for commercial tannic acid is often given as C76H52O46, which corresponds with decagalloyl glucose, but in fact it is a mixture of polygalloyl glucoses or polygalloyl quinic acid esters with the number of galloyl moieties per molecule ranging from 2 up to 12 depending on the plant source used to extract the tannic acid. Commercial tannic acid is usually extracted from any of the following plant parts: Tara pods (Caesalpinia spinosa), gallnuts from Rhus semialata or Quercus infectoria or Sicilian sumac leaves (Rhus coriaria).
Ellagic acid is a polyphenol found in numerous fruits and vegetables. It is the dilactone of hexahydroxydiphenic acid.
Proanthocyanidins are a class of polyphenols found in many plants, such as cranberry, blueberry, and grape seeds. Chemically, they are oligomeric flavonoids. Many are oligomers of catechin and epicatechin and their gallic acid esters. More complex polyphenols, having the same polymeric building block, form the group of condensed tannins.
The enzyme tannase (EC 3.1.1.20) catalyzes the following reaction:
Phenolic compounds—natural phenol and polyphenols—occur naturally in wine. These include a large group of several hundred chemical compounds that affect the taste, color and mouthfeel of wine. These compounds include phenolic acids, stilbenoids, flavonols, dihydroflavonols, anthocyanins, flavanol monomers (catechins) and flavanol polymers (proanthocyanidins). This large group of natural phenols can be broadly separated into two categories, flavonoids and non-flavonoids. Flavonoids include the anthocyanins and tannins which contribute to the color and mouthfeel of the wine. The non-flavonoids include the stilbenoids such as resveratrol and phenolic acids such as benzoic, caffeic and cinnamic acids.
Castalagin is an ellagitannin, a type of hydrolyzable tannin, found in oak and chestnut wood and in the stem barks of Terminalia leiocarpa and Terminalia avicennoides.
A gallotannin is any of a class of molecules belonging to the hydrolysable tannins. Gallotannins are polymers formed when gallic acid, a polyphenol monomer, esterifies and binds with the hydroxyl group of a polyol carbohydrate such as glucose.
The ellagitannins are a diverse class of hydrolyzable tannins, a type of polyphenol formed primarily from the oxidative linkage of galloyl groups in 1,2,3,4,6-pentagalloyl glucose. Ellagitannins differ from gallotannins, in that their galloyl groups are linked through C-C bonds, whereas the galloyl groups in gallotannins are linked by depside bonds.
Quercus infectoria or the Aleppo oak is a species of oak well known for producing galls that have been traditionally used for centuries in Asia medicinally while also used in softening leather and in making black dye and ink.
Hexahydroxydiphenic acid is an organic compound with the formula [(HO)3C6HCO2H]2. It is the oxidatively coupled derivative of gallic acid It is a white solid, although samples are typically brown owing to oxidation.
Valoneic acid is a hydrolysable tannin. It is a component of some hydrolysable tannins such as mallojaponin.
The pomegranate ellagitannins, which include punicalagin isomers, are ellagitannins found in the sarcotestas, rind (peel), bark or heartwood of the pomegranate fruit.
Sanguisorbic acid is a constituent of some ellagitannins. It is constituted by a hexahydroxydiphenic acid unit linked by an O-C bond to a gallic acid. The differences with its isomers, valoneic acid and nonahydroxytriphenic acid, are that the hydroxyl that links the hexahydroxydiphenoyl (HHDP) group to the galloyl group belongs to the galloyl group in valoneic acid, while in nonahydroxytriphenic acid, the hexahydroxydiphenic acid unit is linked by a C-C bond to gallic acid.
Terminalia macroptera is a species of flowering plant in the Combretaceae known by the Hausa common name kwandari. It is native to Africa, where it can be found in Benin, Burkina Faso, Ghana, Senegal, Sudan, Uganda, and Nigeria.
Mallojaponin is a hydrolysable tannin found in the bark of Mallotus japonicus. This compound contains the moiety elaeocarpusinic acid, an oxidized hexahydroxydiphenic acid group which reacted with a dehydroascorbic acid molecule. It also contains a valoneic acid and a gallic acid moieties linked to a glucose molecule.
Tellimagrandin I is an ellagitannin found in plants, such as Cornus canadensis, Eucalyptus globulus, Melaleuca styphelioides, Rosa rugosa, and walnut. It is composed of two galloyl and one hexahydroxydiphenyl groups bound to a glucose residue. It differs from Tellimagrandin II only by a hydroxyl group instead of a third galloyl group. It is also structurally similar to punigluconin and pedunculagin, two more ellagitannin monomers.