Nomenclature
CAS number: 9000-65-1
Tragacanth.
Description and references
Mol wt about 840,000. The dried gummy exudation
from Astragalus gummifer Labill. (white gavan) or other
Asiatic species of Astragalus, Leguminosae, found largely
in Iran, also in Asia Minor and in Syria. When mixed with water gives
a soluble fraction, as a hydrosol, called tragacanthin which is a complex mixture of polysaccharides containing d-galacturonic acid, other sugars, and traces of starch and
cellulose. The insoluble fraction swells to a gel and consists of
60-70% bassorin. Structural studies: Norman, Biochem. J. 25, 200 (1931); James, Smith, J. Chem. Soc. 1945, 739, 749;
Aspinall, Baillie, ibid. 1963, 1702, 1714. Reviews: D. C. Beach in Adv. Chem.
Ser. 11, entitled “Natural Plant Hydrocolloids,”
(ACS, Washington DC, 1954) pp 38-44; Meer et al. in Industrial Gums, R. L. Whistler, Ed. (Academic
Press, New York, 2nd ed., 1973) pp 289-299. Book: F.
Smith, R. Montgomery, The Chemistry of Plant
Gums and Mucilages (Reinhold, New York, 1959) 627 pp.
Properties
Odorless. Insipid, mucilaginous taste. Acid
reaction. One gram requires 0.9 ml 0.1N NaOH for neutralization
to phenolphthalein: Gabel, J. Am. Pharm.
Assoc. 23, 341 (1934). Viscosity of tragacanth
mucilages is reduced by adding acid, alkali, and NaCl particularly
if the mucilage is heated: Mantell, The Water-Soluble
Gums (New York, 1947). Maximum initial viscosity of solns
at pH 8; maximum stable viscosity near pH 5. Forms a deep yellow
stringy precipitate when a soln is boiled with a few drops of 10%
aqueous ferric chloride soln. A stringy precipitate formed also on
heating a soln with Schweitzer reagent. Tragacanth is entirely insol
in alcohol.Use
In pharmaceutical compounding and dispensing,
e.g., to suspend heavy insol 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 insol color lakes.