TANNINS TANNINS TANNINS TANNINS

Tannins

• Tannins is a substance found naturally in many different plants, most in grapes

and tea leaves ,precipitate proteins from their aqueous solutions.

Tannins

• Tannins is a substance found naturally in many different plants, most in grapes

and tea leaves ,precipitate proteins from their aqueous solutions.

Base Unit:

Gallic acid Flavone

Class/Polymer:Hydrolysable tannins condensed tannins

Sources: Plants Plants

Condensed tannin   Hydrolysable Tannin

• On dry distillation they give catechol.

• their structures are related to flavonoids and they lack sugar in their structures

• Present in cinnamon, cinchona and tea.

• consist of several molecules of phenolic acids united by ester linkage to a central glucose residue.Also have potential antibacterial effects against Helicobacter pylori.

Types of hydrolysable tannin:A- Gallitannin On hydrolysis , it gives gallic acid and glucose.Present in clove.. B- Ellagitannin  On hydrolysis it gives ellagic acid and glucose  Present in pomegranate.

Pseudotannins: Pseudo tannins are low molecular weight compounds found in Rhubarb , tea and coffee

Types of hydrolysable tannin:A- Gallitannin On hydrolysis , it gives gallic acid and glucose.Present in clove.. B- Ellagitannin  On hydrolysis it gives ellagic acid and glucose  Present in pomegranate.

Pseudotannins: Pseudo tannins are low molecular weight compounds found in Rhubarb , tea and coffee

Identification of Tannins:1-tannin + ferric chloride (FeCl3) :

Bluish black colour with hydrolysable tannin.

Brownish black colour with catechol.

2-

2-Gelatin test: Solution of tannins (about 5-1%) precipitate 1% Solution of gelatin containing l0 % sodium chloride Gallic acid and other pseudotannins also precipitate. gelatin if the solutions are sufficiently concentrated.

3- Bromine water: only condensed tannin gives ppt. with bromine water.

4-Gold beater's skin test:a soak a small piece of Gold beater's skin

membrane in 2% hydrochloric acid ( HCL).

b- rinse with distilled water.

c- place the piece for 5 minutes in the tannin solution to be tested.

d- wash with distilled water

………

e- transfer to 1% ferrous sulfate (FeSO4) solution.

f- a brown or black colour in the skin denote the presence of tannins.

Quantitative determination of tannin:

1- Hide powder method:The difference in the dry weight of the extract before and after treatment with hide powder is taken as a measure for tannin content.

2- Copper acetate method: Gravimetric method using copper acetate as precipitant.

Uses of Tannins:

Industrially:In leather tanning, ink manufacture.

Medicinally:Astringent, haemostatic, antidiarrheal, antidote in alkaloid and heavy metals toxicity. 

In labs: Reagent for detection of proteins, alkaloids and heavy metals because of their precipitating properties.

Tannin containing drugs :

Galls (Blue Galls, Aleppo Galls, Turkish Galls): Turkish galls are vegetable growths formed on the Young twigs of the dyer’s oak.

Origin of galls :(pathological outgrowth) as a result of the

deposition of the eggs of the gall-wasp Cynips gallae tinctoriae on the young twigs of Quercus infectoria (Fagaceae). They are Collected before the escape of the insect and known as blue galls.

Characters of galls :

1- galls are globular in shape and form l0 to 25 mm in Diameter .

2-They have a short basal stalk and numerous rounded projection on the surface.

3-Galls are hard and heavy, usually sinking in water.

4-external surface is bluish green to olive green in color .Internally it is buff in color.

5- The so-called ‘blue' variety are actually of a grey or brownish-grey color.

 

*Constituents of galls :

Galls contain 50-70% of the tannin known as gallotannic acid. Galls also contain Gallic acid and ellagic acid.

Uses of galls:Medicinally:

1-It is used as astringent

2- haemostatic used in treatment of hemorrhoids in form of suppository or ointment.

Industrially:

1- in manufacture of ink and paints.

2- in tanning of leather.

Commercial test :

Galls + fecl3

Bluish Black color.