Gum Tragacanth

Introduction

Source
Gum Tragacanth, like Gum Arabic, has an ancient history. It was described by Theophrastus several centuries before Christ. It is an exudate of the Astragalus genus of plants of the Leguminosae family. The name tragacanth, from the Greek tragos (goat) and akantha (horn), probably refers to the curved shape of the ribbons, the best grade of commercial gum. It is also available in flakes, and each grade is grown from a specific shrub.The gum exudes spontaneously from breaks or wounds inflicted in the bark of the shrubs. It is usually collected by hand by the natives and carried to collecting and sorting centers where it is graded into several grades of ribbons and flakes and exported.
Gum tragacanth, recognized officially in the United States Pharmacopoeia since 1820, is currently defined as "dried gummy exudation from Astragalus gummifer Labillardiere or other Asiatic species of Astragalus (Fam. Leguminosae)."

Properties

Botanic Characteristics
Tragacanth is available in flattened, lamellated, frequently curved fragments or straight or spirally twisted linear pieces from 0,5 mm to 2,5 mm in thickness. It is white to weak yellow in color, translucent, and horny in texture.
Powdered Tragacanth has a white to yellowish white color and no odour.

Physical Characteristics
When added to water, the soluble tragacanthin dissolves to give a colloidal hydrosol solution, while the insoluble bassorin component swells to a gel-like state. When a small proportion of water is used, a soft, adhesive paste is formed. If more water is added, the paste forms a uniform mixture that separates in 1 or 2 days, with most of the dissolved tragacanthin in the upper layer and the greater portion of insoluble bassorin in the lower layer.
The ability of tragacanth to swell in water to give thick, viscous dispersions or pastes has accounted for many of its uses in the pharmaceutical and food industries. As with most other gums, viscosity is the most important property of the gum tragacanth solution. The viscosity of a 1% solution of the highest grade of gum is about 3400cps. A 2-4% concentration gives a thick paste when properly hydrated. In a cold preparation, the maximum viscosity is usually reached after 24 hours but it can be obtained in about 2 hours by raising the temperature of the solution to about 50°C.Gum tragacanth solutions are acidic, usually in the pH range of 5-6. Its maximum initial viscosity is at pH 8, but its maximum stable viscosity was found to be near pH 5 by Schwarz, who also noted that the stability is definitely decreased at pH below 4 or above 6. Compared to other gums, however, tragacanth is fairly stable over a wide pH range down to extremely acidic conditions at about pH 2. For this reason, it has been widely used in food products such as salad dressings, where stable viscosities at low pH's are required.

Standards

Minimum standards for good quality Gum Tragacanth have been defined in the United States Pharmacopeia USP23:

Arsenic (as As): <= 3ppm
Heavy metals (as Pb): <= 0.004 %
Lead: <= 0.001 %
Karaya Gum: absent
Microbila limits: Salmonella and Escheria coli absent.

Applications

• salad dressings and sauces
• ice cream, ices, and sherbets
• bakery products, pie fillings
• confectionery
• pharmaceutical industries
• cosmetics
• emulsions and suspensions
• and many others.

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