Tannins

Astringent compounds in plants that protect the plant from yeasts, being eaten, and bacterial decay.

Polyphenol plant constituents which bind divalent metal ions such as ferrous iron, zinc, etc. and makes these ions less bioavailable for intestinal absorption from the food. They have an astringent effect in the mouth, precipitate proteins, and are used to clarify beer and wines. Also called tannic acid and gallotannin.

A stringent, bitter phenolic compound.

A group of simple and complex phenol, polyphenol, and flavonoid compounds, bound with starches, and often so amorphous that they are classified as tannins simply because at some point in degradation they are astringent and contain variations on gallic acid. Produced by plants, tannins are generally protective substances found in the outer and inner tissues of plants, often breaking down in time to phlebotannins and, finally, humin. All of the tannins are relatively resistant to digestion or fermentation, and either decrease the ability of animals to easily consume the living plant, or, as in deciduous trees, cause the parts of the plant to decay so slowly that there is little likelihood of infection to the still-living parts of the plant resulting from rotting dead material around its base. All tannins act as astringents, shrinking tissues and contracting structural proteins in the skin and mucosa. Tannin-containing plants can vary a great deal in their physiological effects and should be approached individually.

Astringent principle of many plants.

Secondary metabolites with several phenolic OH-groups, that can form hydrogenand ionic bonds with proteins, thereby altering their conformation; distinguished are gallotannins and catechol tannins, which derive from catechin or epicatechin.

A substance in tea and red wine that contributes to the taste and coloring of the beverage.

Tannic acid. A yellowish astringent compound found in tea.

Polyphenols that are responsible for the astringent nature of teas, cranberries, and other herbs.

A substance found in the bark of trees and in tea and other liquids, which stains brown.

A heterogeneous group of substances in plants. They include all the plant polyphenolic substances with a molecular weight higher than 500. Two types of tannins are distinguished on the basis of their properties, breakdown products, botanical distribution, and whether they are hydrolyzable or condensed tannins. Hydrolyzable tannins are gallic, digallic, and ellagic acid esters of glucose or quinic acid. One type of hydrolyzable tannins is tannic acid (also known as gallotannic acid, gallotannin, or simply tannin). In tannic acid all the hydroxyl groups of glucose are esterified with gallic or digallic acid. It may cause acute liver injury, that is, liver necrosis and fatty liver. The condensed tannins (also known as flavonols) are polymers of flavonoids and in most cases are leucoanthocyanidins. The monomers are linked through carbon-carbon bonds between positions 4 and 6, or positions 4 and 8. The occurrence of tannins is reported in unripe fruits such as mango, dates, and persimmons. The tannins diminish in amounts as the fruits ripen. Furthermore, tannins are found in variable amounts in coffee (regular coffee: 1.1% tannins; instant coffee; 4.3% tannins; decaffeinated ground coffee: 1.2% tannins; instant decaffeinated coffee: 5.2% tannins), cocoa (unsweetened cocoa: 2.5% tannins; cocoa made by treatment with alkali: 4% tannins), and tea (bulk black tea and green tea: 10.5%-! 1.8% tannins; tea bags [black and green tea]: 9.1%-!3.1% tannins; black instant tea: 14.7% tannins). Green tea may yield more soluble tannins, while black tea contains tannins with a higher molecular mass, as a result of oxidation of phenolic precursors during fermentation. Other food sources of tannins are grapes (condensed tannins, on average 500 mg/kg of grapes), grape juice, wines (red wine: 1.2-4.4 g/L of wine), and some sorghum grain varieties.

An acid found in the bark of certain plants and trees or their products, usually from nutgall. It is found in coffee and to a greater extent in tea.

One of a group of complex compounds found in many plants containing acids, phenols and glycosides.