Tannins are complex organic, non-nitrogenous substances that occur as mixtures of polyphenols. They are widely distributed in plants and form colloidal solutions with water. Tannins have various properties including being non-crystallizable, soluble in water and various organic solvents, and causing precipitation of solutions of proteins and metals. They are classified as hydrolysable tannins, condensed tannins, or pseudotannins. Pharmacologically, tannins are used as astringents for the gastrointestinal tract, skin, and eyes. Industrially, they are used in tanning leather, manufacturing inks, and detecting proteins. Common sources of tannins include nut galls, black

1. Tannins

2. Defination of tannin
Tannins are complex organic, non-nitrogenous and non-crystalline
substances, occurs as a mixture of polyphenols and from colloidal
solutions with water that are widely distributed in plant (vegetable)
kingdom.

3. Properties of tannins
1.Tannins are non-crystalysable compound.
2. They are soluble in water and from colloidal solution.
3. They are aquous solution are acidic in nature and posseses a sharp
pungent taste, seen this solution is acidic weak and identify them litmus
paper.
4. They are soluble in dilute alkali, alcohol, glycerol and acetone but
sparingly soluble in other organic solvents.
5. They cause the precipitation of solution of the gelatin, alkaloids,
heavy metal and glycosides.

4. Properties of tannins
6. They formed dark blue and greenish black soluble compound with
ferric salt.
7. They produce a deep red color with potassium ferricyanide at
ammonia.
8. Tannins are precipitate by salt of copper(Cu), lead(Pb), tin(Sn), and
by strong aquous potassium dichromate solution or 1% chromic acid
solution.
9. In alkaloin solution many of their derivatives readily absorb oxygen
from the atmosphere.
10. Tannin precipitate and combine with protein renderning them
resistance to proteolytic enzymes.

5. Classification of tannins
1. Hydrolysable tannins.
2. Condensed tannins.
3. Pseudotannins.

6. Hydrolysable tannins
These tannins are the esters of a sugar usually glucose with
one or more trihydroxy benzo carboxylic acid.They are
hydrolyzed by acids, or enzyme and produce gallic acid
and ellagic acid.

7. Condensed tannins
These tannins are resistant to hydrolysis and they derived from the
flavonols, catechins and flavan-3, 4-diols. On treatment with acids or
enzymes they are decomposed into phlobaphenes. On dry distillation
condensed tannin produce catechol. These tannins are called as
catechol tannins.

8. Pseudotannins
They are phenolic compounds of lower molecular weight
and do not show the goldbeater’s skin test. They occurs as
gallic acid, catechins, chlorogenic acid etc.

9. Pharmacological activity of tannins
Pharmaceutically—
• Tannins are used as an astringent in the GIT and skin abrasions.
• It is used in the treatment of burns.
• It also act as preservative because of its antiseptic properties.
• Tannins are widely used as an application to sprains, bruises and
superficial wounds. (Hamamelis)
• It is used as an ingredient of eye lotions. (Hamamelis)
• It is used as styptic. (Nutgalls)

10. Pharmacological activity of tannins
Industrially—
• It is used in the manufacture of inks.
• Tannins are utilized in the laboratory as astringents for the
detection of gelatin, proteins and alkaloids.
• Tannins are used in the tanning process of animal hides to convert
them into leather.

11. Side effects of tannins
• Absorb tannic acid can cause severe necrosis of the liver.
• Prolonged utilization of certain tannin rich plant materials may be
dangerous owing to their carcinogenic potential. Eg. The habitual
chewing betel nut rich in condensed catechin tannin has been link
to high rate of oral and esophageal cancer in India and South
Africa.

12. Tests for tannins
1. Solution of tannin precipitated heavy metal, alkaloids, glycosides and
gelatin with ferric salt, galli tannins, ellagi tannins, give blue black
precipitate and condensed tannin give brownish green precipitate.
2. Gold beater’s skin test: A membrane prepared or isolated from the
intestine of oxe can be used as gold beater’s skin. Small piece of gold
beater’s skin is soaked in 2% HCL acid, then it is taken out rinsed with
distilled water and placed in the experimental solution of tannin for 5
minutes. Then it is washed with distilled water and transferred to 1% of
ferrus sulphate (FeSO4) solution. A brown or black color on the skin
denotes the presence of tannin.
3. Gelatin test: About 0.5 to 1% solution of tannin is kept in 1% solution
of gelatin containing 10% NaCl. The formation precipitation denotes the
presence of tannin.

13. Tests for tannins
4. Phenozone test: 0.5 gm NaH2PO4 is added to about 5ml of an aquous
extract of the drug. Then it is warned , cooled and filter. 2% solution of
phenozone added to the filtrate. If precipitate occurs it indicate the presence of
tannin.
5. Test for catechin: A match stick is dipped in aqueous plant extract, dried
near burner and moistened with concentrated hydrochloric acid. On warming
near flame, the matchstick wood turns pink or red due to formation of
phloroglucinol.
6. Test for chlorogenic acid: When the extract is treated with aquous NH3
and exposed to air, it gradually develops green color. The development of the
green color denotes the presence of tannin containing chlorogenic acid.

14. Nut gall
Biological source: Quercus infectoria.
Chemical constituents: Gallo tannic acid, gallic acid, ellagic acid, β-
sitosterol, methyl betulate, methyl oleonolate, Ca-oxalate, resin.
Uses:
1. Source of tannic acid.
2. In the tanning and dyeing industry.
3. As astringent and styptic.
4. In the production of ink.

16. Black catechu
Biological source: Acacia catechu
Chemical constituents: Catechin, phlobatannin, gummymaterial,
quercetin, quercitrin.
Uses:
1. Possess cooling and digestive properties.
2. Used in relaxed condition of throat and mouth.
3. As astringent in skin eruptions.

18. Hamamelis leaf
Biological source: Hamamelis virginiana.
Chemical constituents: Galli tannin, ellagi tannin, gallic acid,
proanthocyanidin, Ca-oxalate.
Uses:
1. Astringent.
2. Used in the preparation of trating insect bite, sting bite etc.
3. Used in tooth prepation, eye lotion.
4. As flavoring agents.

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