Tragacanth gum

Chemical Properties

Gum tragacanth is the dried exudate from several species of Astragalus (A. gummifer Labillardiere, or other Asiatic species of Astragalus), a shrub that grows wild in mountainous regions of the Middle East, particularly Iran. The gum is obtained by making incisions in the taproots of the plant; to a lesser extent, the branches also are tapped. The gum exudate is in the form of curled ribbons or flakes, which become horny on drying. Collections are made by hand in May to October and are sorted, graded, packed and shipped. The processor then further grades, cleans, mills and blends the gum, and sells it in the form of ribbons, flakes, granules or powder.

Chemical Properties

light beige powder

Chemical Properties

Tragacanth gum occurs as flattened, lamellated, frequently curved fragments, or as straight or spirally twisted linear pieces from 0.5–2.5mm in thickness; it may also be obtained in a powdered form. White to yellowish in color, tragacanth is a translucent, odorless substance, with an insipid mucilaginous taste.

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.

Uses

Tragacanth is a gum produced from a bush of the genus astragalus. It swells in water to give a highly viscous sol or paste. A 1% solution of the purest gum has a viscosity of approximately 3,400 cps, and about 2% can form a paste. Solutions have a ph of 5–6. It is stable at low ph and is an effective suspending agent because of its stability and acid resistance. It is used in salad dressings, sauces, fruit fillings, and citrus beverages. It is also termed gum tragacanth.

Uses

tragacanth gum is an effective emulsifying agent, binder, film former, and viscosity controller, it is also used as a stabilizing ingredient in lotions. Tragacanth gum is derived from the resin of the Astragalus gummifer shrub.

Uses

In pharmaceutical compounding and dispensing, e.g., to suspend heavy insoluble powders, as an excipient for tablets and to impart consistence to troches; also in making emulsions and emulsifying agents; as stabilizer, thickener, texturizer in food; in adhesives (mucilages, pastes); in textile sizing, textile printing and general printing inks, and in dyeing with insoluble color lakes.

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 Profile

Mildly toxic by ingestion. A mild allergen. A skin and eye irritant. Combustible when exposed to heat or flame. When heated to decomposition it emits acrid smoke and irritating fumes.

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.