Chemical Properties
light beige powder
Physical properties
As collected, tragacanth is white to weak yellow, translucent; horny in texture, having a short
fracture. It is rendered more easily pulverizable if heated to 50°C. Powdered tragacanth is white to yellowish white. Gum tragacanth
swells in cold water to give extremely viscous colloidal solutions, probably the most viscous of all the plant gums.
Production Methods
Tragacanth gum is the air-dried gum obtained from Astragalus
gummifer Labillardie`re and other species of Astragalus grown
principally in Iran, Syria, and Turkey. A low-quality gum is obtained by collecting the natural air-dried exudate from Astragalus
bushes. A higher-grade material is obtained by making incisions in
the trunk and branches of the bush, which are held open with
variously sized wooden pegs. The exudate is left to drain from the
incision and dry naturally in the air before being collected. The size
and position of the wooden wedges determine the physical form of
the exudate, while the drying conditions determine the color of the
gum. After collection, the tragacanth gum is sorted by hand into
various grades, such as ribbons or flakes.
General Description
Tragacanth is a gum commonly found in the sap of various Middle Eastern legumes. It is commonly used as freezing-embedding medium for tissue preservation.
Pharmaceutical Applications
Tragacanth gum is used as an emulsifying and suspending agent in a
variety of pharmaceutical formulations. It is used in creams, gels,
and emulsions at various concentrations according to the application
of the formulation and the grade of gum used.
Tragacanth gum is also used similarly in cosmetics and food
products, and has been used as a diluent in tablet formulations.
Safety
Tragacanth has been used for many years in oral pharmaceutical
formulations and food products, and is generally regarded as an
essentially nontoxic material. Tragacanth has been shown to be
noncarcinogenic. However, hypersensitivity reactions, which are
occasionaly severe, have been reported following ingestion of
products containing tragacanth. Contact dermatitis has also
been reported following the topical use of tragacanth formulations.
The WHO has not specified an acceptable daily intake for
tragacanth gum, as the daily intake necessary to achieve a desired
effect, and its background levels in food, were not considered to be a
hazard to health.
LD50 (hamster, oral): 8.8 g/kg
LD50 (mouse, oral): 10 g/kg
LD50 (rabbit, oral): 7.2 g/kg
LD50 (rat, oral): 16.4 g/kg
storage
Both the flaked and powdered forms of tragacanth are stable.
Tragacanth gels are liable to exhibit microbial contamination with
enterobacterial species, and stock solutions should therefore
contain suitable antimicrobial preservatives. In emulsions, glycerin
or propylene glycol are used as preservatives; in gel formulations,
tragacanth is usually preserved with either 0.1% w/v benzoic acid
or sodium benzoate. A combination of 0.17% w/v methylparaben
and 0.03% w/v propylparaben is also an effective preservative for
tragacanth gels. Gels may be sterilized by
autoclaving. Sterilization by gamma irradiation causes a marked
reduction in the viscosity of tragacanth dispersions.
Tragacanth dispersions are most stable at pH 4–8, although
stability is satisfactory at higher pH or as low as pH 2.
The bulk material should be stored in an airtight container in a
cool, dry place.
Incompatibilities
At pH 7, tragacanth has been reported to considerably reduce the
efficacy of the antimicrobial preservatives benzalkonium chloride,
chlorobutanol, and methylparaben, and to a lesser extent that of
phenol and phenylmercuric acetate. However, at pH < 5
tragacanth was reported to have no adverse effects on the
preservative efficacy of benzoic acid, chlorobutanol, or methylparaben.
The addition of strong mineral and organic acids can reduce the
viscosity of tragacanth dispersions. Viscosity may also be reduced
by the addition of alkali or sodium chloride, particularly if the
dispersion is heated. Tragacanth is compatible with relatively high
salt concentrations and most other natural and synthetic suspending
agents such as acacia, carboxymethylcellulose, starch, and sucrose.
Ayellow colored, stringy, precipitate is formed with 10% w/v ferric
chloride solution.
Regulatory Status
GRAS listed. Accepted for use as a food additive in Europe.
Included in the FDA Inactive Ingredients Database (buccal/
sublingual tablets, oral powders, suspensions, syrups, and tablets).
Included in nonparenteral medicines licensed in the UK. Included in
the Canadian List of Acceptable Non-medicinal Ingredients.
