Karaya Gum

KARAYA GUM

Synonyms

Indian tragacanth, Sterculia gum, Karaya gum, Bassora tragacanth, kadaya, mucara, kadira, katila, kullo.

Biological Source

Gum karaya is a dried, gummy exudates obtained from the tree Sterculia urens (Roxburgh); Sterculia villosa (Roxburgh), Sterculia tragacantha (Lindley) or other species of Sterculia, belonging to family Sterculiaceae.

Geographical Source

The S. urens is found in India especially in the Gujarat region and in the central provinces.

Collection and Preparation

The gum is obtained from the Sterculia species by making incisions and, thereafter, collecting the plant exudates usually after a gap of 24 h. The large irregular masses of gums (tears) which weigh between 250 g to 1 kg approximately are hand picked and dispatched to the various collecting centres. The gum is usually tapped during the dry season spreading over from March to June. Each healthy fully grown tree yields from 1 to 5 kg of gum per year; and such operations may be performed about five times during its lifetime. In short, the large bulky lumps (tears) are broken to small pieces to cause effective drying. The foreign particles, for example, pieces of bark, sand particles and leaves are removed. Thus, purified gum is available in two varieties, namely:

1)    Granular or Crystal Gum: Having a particle size ranging between 6 to 30 mesh, and

2)    Powdered Gum: Having particle size of 150 mesh

Morphology

                                  Karaya twig

History

Karaya gum has been used commercially for about 100 years. Its use became widespread during the early 20th century, when it was used as an adulterant or alternative for tragacanth gum. However, experience indicated that karaya possessed certain physiochemical properties that made it more useful than tragacanth; furthermore, karaya gum was less expensive. Traditionally, India is the largest producer and exporter of karaya gum. Increasing amounts are exported by African countries. Currently the gum is used in a variety of products, including cosmetics, hair sprays, and lotions, to provide bulk. The bark is astringent.

Chemical Constituents

Karaya gum is partially acetylated polysaccharide contain-ing about 8% acetyl groups and about 37% uronic acid residues. It undergoes hydrolysis in an acidic medium to produce D-galactose, L-rhamnose, D-galacturonic acid and a trisaccharide acidic substance. It contains a branched heteropolysaccharide moiety having a major chain of 1, 4-linked α- D-galacturonic acid along with 1, 2-linked L-rhamnopyranose units with a short D-glucopyranosy-luronic acid containing the side chains attached 1→3 to the main chain, that is, D-galactouronic acid moieties.

Chemical Test

1) To 1 g of powdered Karaya Gum, add 50 ml of water and mix. A viscous solution is produced and it is acidic.

2) Add 0.4 g of powdered Karaya Gum to 10 ml of an ethanol-water mixture (3:2), and mix. The powder is swelling.

3) It readily produces a pink colour with a solution of ruthenium red.

Uses

Karaya gum is not digested or absorbed systemically. Medici-nally, karaya gum is an effective bulk laxative, as gum par-ticles absorbs water and swells to 60–100 times their original volume. The mechanism of action is an increase in the volume of the gut contents. Karaya gum should be taken with plenty of fluid and it may take a few days for effects to be noticeable. It also has been used as an adhesive for dental fixtures and ostomy equipment, and as a base for salicylic acid patches. The demulcent properties of the gum make it useful as an ingredient in lozenges to relieve sore throat. A protective coating of karaya gum applied to dentures has been shown to reduce bacterial adhesion by 98%. The use of karaya gum as a carrier for drugs with differing solubility in aqueous medium has been investigated. In pharma industry, it is also used as emulsifier, thickener and stabilizer. Karaya gum is also used in paper and textile industries.

Adulterant and Substitutes

It is used as a substitute for gum tragacanth.