Pharmacognosy of Guar Gum

Devesh

Devesh


Synonyms

guar floor, Jaguar gum.

Biological source

Guar gum is the powder of the endosperm is the seed of cyamopsis Tetragonolobus Linn, belonging to family Leguminosae.

Geographical source

It has been grown for centuries in India and Pakistan and was introduced in 1900 in USA. It’s commercial production was started in 1953.

Preparation

Guar gum is industrially manufactured from the white, well developed seeds that are freed from foreign matter. The seeds are separated into husk and cotyledons containing embryo. The history contain fibrous matter and the gum is located into endosperm. Guar seeds contains 14-17% of hull, 35-40% of endosperm and 45-50% of germ cotyledons separated from the endosperm by winnowing and sifting fetch very high price in the market as a cattle feed. The endosperm i.e. crude guar gum is pulverized by means of micro pulverizer and grinding for 15 minutes. The endosperm being harder is not affected by micro pulverizer. The portion of cotyledons adhering to the endosperm is soft and is converted into fine powdered which is separated by sifting. The crude guar gum is now free of cotyledons, the main impurity in the gum. The crude guar gum thus separated is put into pulverizer and grinding is continued for 3 to 4 hours followed by sifting. The process is repeated about 5 to 6 times for several hours to give white coloured guar gum. Finally, it is sifting through sieves of 40 to 60 mesh to give granular and powdered gum. In India, about 15 units are producing guar gum on industrial scale.

Cyamopsis tetragonolobus plant

Description

It is colourless or pale yellowish white coloured powered with characteristic odour and gummy taste. Guar gum swells rapidly in water with a translucent suspension. 0.5% aqueous solution of gum is neutral to litmus.

Standards

Ash: not more than 1%

Acid-insoluble ash: not more than 0.5%

Loss on drying: not more than 8%

Chemical Constituents

The content of guar gum are divided into water soluble and water insoluble parts. The water soluble fraction constituting about 85% of the gum is known as guaran, which is a high molecular weight hydro colloidal polysaccharide. Guaran on hydrolysis yeild 65% galactos and 35% of mannose which is combined through glycosides linkage. Guar gum also contain 5-7% of proteins.

The proposed structure of guaran is given here

Guaran Structure

Identification

  1. It does not acquired olive green colour with weak solution of iodine
  2. With solution of ruthenium red, the gummy solution does not acquire pink colour (distinction from agar and sterculia gum).
  3. About 2% solution of lead acetate gives precipitate with the solution of guar gum.
  4. Dissolve 0.5 g of guar gum in 20 ml of water by shaking. To it add 0.5 ml hydrogen peroxide and 0.5 ml. 1% solution of benzidine in alcohol. No blue colour is produced (distinction from gum acacia).

Uses

About 1% mucilage of guar gum possesses similar viscosity to that of mucilage of acacia and 3% mucilage is similar to mucilage of tragacanth. It has 5 to 8 times thickening power than starch. It is used as a protective colloid, a binding and disintegration agent. Industrially, this is used in paper manufacturing, printing, polishing, textiles and also in food and cosmetic industries.

It is extensively used as flocculent in ore-dressing and treatment of water.

Export of guar gum during 95-96 and 96-97 was to the tune of Rs 226 crores and 354 crores respectively.