Tannins

TANNINS

GENERAL INFORMATION ABOUT TANNINS:

Plants accumulate a wide variety of “secondary” compounds including alkaloids, terpenes and phenolics. Altough these compounds apparently do not function in primary metabolism such as biosynthesis, biodegradation and other energy conversions of intermediary metabolism, they do have reverse biological activities ranging from toxicity to hormonal mimcry and may play a role in protecting plants from herbivory and disease.

Phenolic metabolism in plants is complex , and yields a wide array of compounds ranging from the familiar flower pigments (anthocyanidins) to the complex phenolics of the plant cell wall (lignin). However, the group of phenolic compounds known as tannins is clearly distinguished from other plant secondary phenolics in their chemical reactivities and biological activities.

The word tannin is very old, comes from the ancient Celtic word for oak and reflects a traditional technology. "Tanning" (waterproofing and preserving) was the word used to describe the process of transforming animal hides into leather by using plant extracts from different plant parts of different plant species.

• Plant parts containing tannins include bark, wood, fruit, fruitpods, leaves, roots, and plant galls.

• Examples of plant species used to obtain tannins for tanning purposes are wattle (Acacia sp.), oak (Quercus sp.), eucalyptus (Eucalyptus sp.), birch (Betula sp.), willow (Salix caprea), pine (Pinus sp.), quebracho (Scinopsis balansae) .

Tannins are astringent, bitter-tasting plant polyphenols that have the ability to bind and precipitate proteins. Although 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. They can complex with proteins, starch, cellulose and minerals.

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