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 organic compounds characterized by multiples of phenol units. They are abundant in plants and structurally diverse. Polyphenols include 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).
Mimosa tenuiflora, syn. Mimosa hostilis, also known as jurema preta, calumbi (Brazil), tepezcohuite (México), carbonal, cabrera, jurema, black jurema, and binho de jurema, is a perennial tree or shrub native to the northeastern region of Brazil and found as far north as southern Mexico, and the following countries: El Salvador, Honduras, Panama, Colombia and Venezuela. It is most often found in lower altitudes, but it can be found as high as 1,000 m (3,300 ft).
Euphorbia helioscopia, the sun spurge or madwoman's milk, is a species of flowering plant in the spurge family Euphorbiaceae. It is a herbaceous annual plant, native to most of Europe, northern Africa, and eastward through most of Asia.
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 tannins.
Procyanidins are members of the proanthocyanidin class of flavonoids. They are oligomeric compounds, formed from catechin and epicatechin molecules. They yield cyanidin when depolymerized under oxidative conditions.
The enzyme tannase (EC 3.1.1.20) catalyzes the following reaction:
The phenolic content in wine refers to the phenolic compounds—natural phenol and polyphenols—in wine, which 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.
A hydrolyzable tannin or pyrogallol-type tannin is a type of tannin that, on heating with hydrochloric or sulfuric acids, yields gallic or ellagic acids.
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.
Condensed tannins are polymers formed by the condensation of flavans. They do not contain sugar residues.
Rhus chinensis, the Chinese sumac or nutgall tree, is a deciduous shrub or small tree in the genus Rhus. Growing to 6 m (20 ft) tall, it has downy shoots and leaves comprising several leaflets. These turn red in autumn before falling.
Biflavonoids are a type of flavonoids with the general formula scheme (C6-C3-C6)2.
Tergallic acids are trimers of gallic acid, often found naturally in the form of glycosides. Tergallic acid O- or C-glucosides that can be found in acorns of several Quercus (oak) species. The dehydrated tergallic acid C-glucoside and tergallic acid O-glucoside can be characterised in the acorns of Quercus macrocarpa. Dehydrated tergallic-C-glucoside can be found in the cork from Quercus suber.
Luteic acid is a natural phenol found in numerous fruits. It is a monolactonized tergalloyl group. Maximilian Nierenstein showed in 1945 that luteic acid was a molecule present in the myrobalanitannin, a tannin found in the fruit of Terminalia chebula and is an intermediary compound in the synthesis of ellagic acid. It can form from hexahydroxydiphenic acid. It is also present in the structure of the tannins alnusiin and bicornin.
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.
Cassandra Leah Quave is an American ethnobotanist, herbarium curator, and associate professor at Emory University. Her research focuses on analyzing natural, plant-based medicine of indigenous cultures to help combat infectious disease and antibiotic resistance. In particular, she studies bacterial biofilm inhibition and quorum-sensing inhibition of botanical extracts for inflammatory skin conditions.
