Gum tragacanth (E413) is the natural exudate gum obtained from small shrubs of the Astragalus species, mainly located in southwest Asia.

Gum tragacanth consists of two fractions: an insoluble component generally called bassorin (60-70%) of the gum), and a water-soluble component generally called tragacanthin. The ratio of these components varies from species to species and partly explains the viscosity differences in commercial samples.

Tragacanth gums hydrate in water to give viscous, slightly long solutions and pastes. Solutions are pseudoplastic with a reversible decrease in apparent viscosity as shear rate is raised. The high viscosity at low shear, coupled with charge repulsion effects, suspend fine particles in solution and help stabilise oil in water emulsions. The maximum viscosity is found at pH 8 but the gum is most stable at its natural pH of 5.

Dispersions of Tragacanth are more stable to acids than those of other gums. The addition of small quantities of sugar does not unduly affect the viscosity, however the addition of salt however lowers the viscosity. Gum Tragacanth shows good stability to freeze-thaw cycling. Autoclaving lowers the viscosity of properly dispersed samples.

Gum Tragacanth reduces interfacial tension and increases solution viscosity, which helps stabilise oil in water emulsions.