International Numbering System (INS) for Food Additives: 413
Food additives Europe numbers: E413
Functional Category
Suspending agent; viscosity-increasing agent.
Applications in Pharmaceutical Formulation
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.
Description
Tragacanth gum occurs as flattened, lamellated, frequently curved fragments, or as straight or spirally twisted linear pieces from 0.5–2.5 mm 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.
Stability and Storage Conditions
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;(1) see also Section 12. Gels may be sterilized by autoclaving. Sterilization by gamma irradiation causes a marked reduction in the viscosity of tragacanth dispersions.(2) 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.(3) However, at pH < 5 tragacanth was reported to have no adverse effects on the preservative efficacy of benzoic acid, chlorobutanol, or methylparaben.(1) 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. A yellow colored, stringy, precipitate is formed with 10% w/v ferric chloride solution.
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.(4) However, hypersensitivity reactions, which are occasionaly severe, have been reported following ingestion of products containing tragacanth.(5,6) Contact dermatitis has also been reported following the topical use of tragacanth formulations.(7) 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.(8) LD50 (hamster, oral): 8.8 g/kg(9) LD50 (mouse, oral): 10 g/kg LD50 (rabbit, oral): 7.2 g/kg LD50 (rat, oral): 16.4 g/kg