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T NN NS

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Definition of Tannins

(Cantoria, 1990)

Tannins are amorphous, polyhydroxy phenolic

compounds with molecular weights in the

range of from about 1,000 to 5,000 which

possess an astringent taste and the ability tocombine with hide to form leather.

TANNIN CELL

IN

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Characteristics of Tannins

Widely distributed in plants and many are

glycosides ex. Glucogallin

Occur in solution in cell sap

Usually found in great quantities

in dead or dying cells

Exert inhibitory effect on enzymes by proteinprecipitation, thus becoming a protectant for

barks and heartwoods.

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GALLOTANNIN or Tannic Acid usually occurs in

the bark and fruit of a large number of plants,such as:

1. dried beans of Coffea arabica L.(Rubiaceae)-Arabica Coffee,

Arabian Coffee, Abyssinian Coffee

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2. fresh forage (fodder) of

Equisetium arrense L. (Equisetaceae)

3. Roots of Glycyrrhiza glabra L. (Fabaceae)

-Common Licorice, Licorice Root,

Spanish Licorice Root

4. juice of the plant of Rhamnus

purshianus DC. (Rhamnaceae)-

Cascara Sagrada, Cascara

buckthorn

5. flowers and plants of Verbena officinalis L.

(Verbenaceae)-Vervain, Verbena.

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GALLOTANNIN or Tannic Acid

Identification Tests

1. Tannic acid, when heated to 210-215C, gets

decomposed to yield pyrogallol and CO2. The

evolution of CO2 may be confirmed when it turns

freshly prepared lime-water milky.

Tannic Acid heated at 210215C Pyrogallol + CO2

2. It instantly gives rise to insoluble precipitates with

albumin, starch, gelatin and a host of alkaloidal and

metallic salts.

3. It readily forms a bluish-black color or precipitate

with ferric salts e.g., FeCl3.

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GALLOTANNIN or Tannic Acid

Uses

1. Tannic acid with ferric salts are invariably used in themanufacture of inks.

2. It is used for tanning i.e., making leather from hides ofcow, goat, sheep and buffalo skin.

3. It is employed as a pharmaceutical aid due to its

astringent and antiseptic actions.4. It is used as a mordant in dyeing.

5. It is invariably employed to clarify beer and wine.

6. It is employed as a coagulant in the manufacture of

rubber.7. It is used in the large scale production of gallic acid andpyrogallol.

8. It is employed as a reagent in analytical chemistry.

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ELLAGITANNINSThey may be derived by the oxidative

coupling of two molecules of gallic acid

which are esterified to glucose orprobably by the condensation of

hydroaromatic precursors.

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COMPLEX TANNINS

This has been applied by Okuda to anewly-discovered group of tanninswhich are biosynthesized from both a

hydrolyzable tannin (mostly C-glucosideellagitannin) and a condensed tannin.

The union through a C-C bondbetween the C1 of the glucose unit of

the ellagitannin and the C8 or C6 of theflavan-3-ol derivative.

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Main Classes of Tannins

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HYDROLYZABLE TANNINS (also referred to as

pyrogallotannins)

1. When treated with acids or enzymes, they yieldphenolic acids, such as gallic and ellagic acids, and

carbohydrates usually glucose.

2. Their solution turn bluish black with FeCl3 TS

3. On dry distillation, gallic acid and similar

components are converted into pyrogallol.


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CONDENSED TANNINS (PHLOBATANNINS,

FLAVOLANS OR CATECHOL TANNINS)

1. They are more resistant when treated with acidsor enzymes as compared to hydrolyzable tannins.

They are decomposed to red insoluble compounds

known as phlobaphenes or tanners red.

2. Their solution turn greenish black with FeCl3 TS

3. On dry distillation, gallic acid and similar

components are converted into catechol.


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PSEUDOTANNINS are compounds of lower molecular

weights than true tannins and they do not respond

to the goldbeaters skin test.

Examples:

Depsides formed by ether linkages between two or

more molecules of phenolic acids (ex. m-gallic acid

in galls , chlorogenic acid in coffee)Derivatives of flavan or phenyl-2-benzodihydropyran

(ex. Catechins or catechols in gambir and kremeria)


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Tannin Formation

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Tannin Formation

Polygalloylgiucose is the parent compound of many, if

not all, of the hydrolyzable tannins.

Catechins and flava-3,4-diols appear to be the

intermediate In the biosynthesis of condensed tannins

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Useful Tests for Tannins

1. Goldbeaters skin test. a brown or black color on the skindenotes the presence of tannins

Golbeaters skin is a membrane prepared from the intestine ofthe ox and behaves similarly to an untanned hide.

2. Gelatin test. Gallic acid and other pseudotanninsprecipitate gelatin if the solutions are sufficientlyconcentrated.

3. Phenazone test. All tannins are precipitated, the precipitatebeing bulky and often colored.

4. Test for Catechin. The phlorogloucinol produced turns thewood pink or red.

5.Test for chlorogenic acid. Development of a green color.

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TANNIN APPLICATIONS

Has the property of precipitating proteins,thusact therapeutically as astringent, both on theGIT and skin abrasions

Tanning leather Precipitates alkaloids, thus used for their

detection and antidotal treatment of toxic

overdoses of these substances Forms deep colored compounds with iron

salts, thus used in the manufacture of inks

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PART USED LOCAL NAME BOTANICALORIGIN

LEAF Hamamelis Hamamelis virginiana

Fam. Hamamelidaceae

Bayabas Psidium guajava L.

Fam. Myrtaceae

Dried aqueous extract Gambir Uncaria gambir(Fam. Rubiaceae)

Excrecence Nutgall Formed on young twigs of Qurcus

infectoria (Fam. Fagaceae) by the gall

wasp,Adleria gallaetinctoriae

Bark Duhat Syzygium cumini(L.) Skeels

Fam. Myrtaceae

Kamachile Pithecolobium dulce (Roxb.) Benth.

Fam. Fabaceae

6. tannins

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