1. Tannins They are high molecular weight phenolic compounds capable of precipitation of animal proteins in hides and converting them into leather. “Tanning Industry” They are widely distributed in plants. They are condensation products of Gallic acid or Flavan-3-ol.

2. Classification of Tannins:

3. Pyrogallol Tannins Composed of central sugars with all its OH esterified with Phenolic acids. Composed of central sugars with all its OH esterified with Phenolic acids. They can be hydrolyzed by acids or enzymes. They can be hydrolyzed by acids or enzymes. They produce sugars and: They produce sugars and: Gallic acid Gallitannins. Present in Clove, Hammamilis Gallic acid Gallitannins. Present in Clove, Hammamilis Ellagic acid Ellagitannins. Present in Geranium Ellagic acid Ellagitannins. Present in Geranium Produce pyrogallol on dry distillation. Produce pyrogallol on dry distillation.

4. Catechol (Condensed) Tannins Condensation product of Flavan-3,4-diol. Condensation product of Flavan-3,4-diol. They resist hydrolysis. They resist hydrolysis. Upon prolonged heating they decompose into Phlobaphane. Upon prolonged heating they decompose into Phlobaphane. Produce catechol on dry distillation. Produce catechol on dry distillation. Present in Cinchona, Cinnamon, Green tea. Present in Cinchona, Cinnamon, Green tea.

5. Properties: Soluble in water, polar organic solvents and Alkali solutions. Soluble in water, polar organic solvents and Alkali solutions. React with FeCl 3 as they are Phenolic. React with FeCl 3 as they are Phenolic. Precipitate proteins and Gelatin. Precipitate proteins and Gelatin. Form with alkaloids and Glycosides. Form with alkaloids and Glycosides.

6. Chemical test for Identification: FeCl 3 : FeCl 3 : Hydrolysable tannins Bluish colour. Hydrolysable tannins Bluish colour. Condensed tannins Greenish colour. Condensed tannins Greenish colour. Goldbeater’s Skin test (Ox-Intestine): Goldbeater’s Skin test (Ox-Intestine): Soak piece of Goldbeater’s skin in 2%HCl, wash with water, soak in test solution, wash with water, finally soak with FeSO 4 Brown or Black colour. Soak piece of Goldbeater’s skin in 2%HCl, wash with water, soak in test solution, wash with water, finally soak with FeSO 4 Brown or Black colour. Gelatin test: Gelatin test: Tannins + 1% Gelatin solution in NaCl white precipitate Tannins + 1% Gelatin solution in NaCl white precipitate

7. Uses: Antioxidant. Antioxidant. Antidiarrheal. Antidiarrheal. Antidote for heavy metals poisoning. Antidote for heavy metals poisoning. Treatment of burns. Treatment of burns. Astringent to stop bleeding (Haemorrhoids, Ulcers). Astringent to stop bleeding (Haemorrhoids, Ulcers).

8. Green and Black Tea Green Tea: Green Tea: Prepared by rapid drying at elevated temperature to deactivate the enzymes. Prepared by rapid drying at elevated temperature to deactivate the enzymes. Contain Catechins with high antioxidant properties. Contain Catechins with high antioxidant properties. Black Tea: Black Tea: Undergo slow drying (Fermentation). Undergo slow drying (Fermentation). Enzyme action resulted in Hydrolysis and Oxidation. Enzyme action resulted in Hydrolysis and Oxidation. Antioxidant properties is greatly decreased. Antioxidant properties is greatly decreased.