Tragacanth

The swelling, gel-forming fraction of gum tragacanth. On contact with water it does not dissolve but hydrates into a viscous gel, giving the gum its high water-binding capacity and its traditional use as a bulking, demulcent and suspending agent.

The soluble fraction, largely a polyarabinogalactan associated with tragacanthic (galacturonic) acid; on hydrolysis it yields arabinose, galactose and uronic acids. It produces the colloidal viscosity that makes the gum an effective emulsifier and stabiliser.

A branched galacturonic-acid backbone bearing arabinose, xylose, fucose and galactose. It is chiefly responsible for the gum's high viscosity at low concentration and its behaviour as a hydrocolloid thickener.

As in other Astragalus species, small amounts of isoflavonoids and phenolics occur in the vegetative tissue, contributing modest antioxidant activity; they are not the medicinally relevant part of the plant, which is the exuded gum.

Astragalus species characteristically contain cycloartane saponins; only trace levels are reported in the tissues of the cushion-forming Mediterranean congeners, and they have no established therapeutic role for this species.

Traditionally a small amount of the dried gum is soaked in water to form a mucilage used as a soothing demulcent for sore throat and cough, and pharmaceutically as a suspending and emulsifying agent. Conservation note: Astragalus tragacantha (astragale de Marseille) is a rare, legally protected species in France and other Mediterranean countries and its wild populations must not be harvested; commercial gum tragacanth of commerce is obtained from other Astragalus species (e.g. A. gummifer, A. gossypinus).

Dispersed as a hydrocolloid to thicken and stabilise lotions, pastes and food products. As an inert bulk agent it is generally regarded as safe, though rare hypersensitivity reactions to tragacanth have been reported.