Gum karaya (Sterculia urens, fam. Sterculiaceae)


Gum karaya, also known as Sterculia gum is the exudate obtained from species of Sterculia;

Commercial quantities of gum are collected from Sterculia urens (family Sterculiaceae) growing in India or from Sterculia setigera found in Africa (Mali, Senegal, Sudan).

Gum karaya – INS 416; E416; GRAS 21 CFR 1841349; European Pharmacopea 01/2005 – is defined by the food regulation as “a dried exudation from the stems and branches of strains of Sterculia urens Roxburgh and other species of Sterculia (family Sterculiaceae) or from Cochlospermum gossypium A.P.De Candolle or other species of Cochlospermum (family Bixaceae)“ (EC regulation  231/2012).

Sterculia trees exude after taping of the trunks. Harvest is done during the dry season.Big lumps are broken down  into smaller pieces before hand selection  to remove the biggest bark impurities.Raw gum is graded upon colour (pale yellow to brown) and impurities (BFOM content). Gum karaya has a specific acetic acid odour.

Due to strong swelling capacity in water, further purification can only be made by dry process. 

After selection of the batches of raw material, gum is mechanically ground. After grinding, sieving, densimetric table treatment and air selection are used to allow further removal of impurities. Specific methods of heat treatment can sterilise the gum.

Gum karaya could be commercialised in kibbled form (pieces around 3mm size; pharmaceutical uses) or in fine powder form (around 100µ; food uses).

Gum karaya is a complex, highly branched, partially acetylated polysaccharide with high molecular weight (up to 16 million daltons). The chemical structure contains about 40% uronic acids residues and 8 to 14 % of acetyl groups which explain the characteristic acetic acid smell. 

Gum karaya exhibits strong swelling capacity; one gram can absorb 50 times his weight of water, giving a viscous colloidal dispersion. When hydrated in water, speed of hydration and final viscosity depends on mesh size of the gum. Stability of   water dispersions is good in acidic medium but weak in high pH medium (> pH 8) due to de acetylation of the molecule. 

Most of the applications of gum karaya are for pharmaceutical specialities.
Meanwhile some “niches” are still found for specific purposes in food formulations;
Gum karaya is used as stabiliser, often in association with other natural gums having emulsifying properties (acacia gum), to produce stable acidic liquid emulsions (flavour emulsions for soft drinks, sauces and dressing)
Pharmaceutical specialities using gum karaya for adhesive and film forming properties are colostomy rings and dental adhesives.
Swelling capacity of gum karaya in granules explains the application for formulations of bulk laxatives as active ingredient.