Tragacanth

TRAGACANTH

Synonyms

Goat’s thorn, gum dragon, gum tragacanth, hog gum.

Biological Source

It is the air dried gummy exudates, flowing naturally or obtained by incision, from the stems and branches of Astra-galus gummifer Labill and certain other species of Astragalus, belonging to family Leguminosae.

Geographical Source

Various species of Astragalus which yield gum are abundantly found in the mountainous region of Turkey, Syria, Iran, Iraq and the former U.S.S.R. at an altitude of about 1,000–3,000 m. Two important varieties of tragacanth, that is, Persian tragacanth and Smyrana or Anatolian tragacanth come from Iran and turkey respectively. In India it is found wild in Kumaon and Garhwal region.

The approximate distribution of a number of gum-producing species found in the areas where tragacanth is collected is shown in Table below.

Table : Distribution of gum producing Astragalus species.

Cultivation, Collection and Preparation

Most of the plants from which tragacanth is collected grow at an altitude of 1,000–3,000 m. The shrubs are very thorny; each of their compound leaves has a stout, sharply pointed rachis which persists after the fall of the leaflets. The mode of collection varies somewhat in different districts, but the following details of collection in the province of Far are typical.

Gums can be obtained from the plants in their first year but is then said to be of poor quality and unfit for commercial use. The plants are therefore tapped in the second year. The earth is taken away from the base to depth of 5 cm, and the exposed part is incised with a sharp knife having a thin cutting edge. A wedge-shaped piece of wood is used by the collector to force open the incision so that the gum exudes more freely. The wedge is generally left in the cut for some 12–24 h before being withdrawn. The gum exudes and is collected 2 days after the incision.

Some of the plants are burned at the top after having had the incision made. The plant then sickens and gives off a greater quantity of gum. However, this practice is not universal, as many plants can not recover their strength and are killed by the burning. The gum obtained after burning is of lower quality than that obtained by incision only, and is reddish and dirty looking. The crop becomes available in August–September.

After collection, the gum is graded as ribbons and flakes which are further categorized into various sub-grades on the basis of shape, size and colour (Table below). The best grades form the official drug, while the lower grades are used in the food, textile and other industries.

Table : Grades of Tragacanth

Morphology

                            Astragalus gummifer

Chemical Constituents

Interestingly, tragacanth comprises two vital fractions: first, being water soluble and is termed as ‘tragacanthin’ and the second, being water insoluble and is known as ‘bassorin’. Both are not soluble in alcohol. The said two components may be separated by carrying out the simple filtration of very dilute mucilage of tragacanth and are found to be present in concentrations ranging from 60% to 70% for bassorin and 30–40% for tragacanthin. Bassorin actually gets swelled up in water to form a gel, whereas tragacanthin forms an instant colloidal solution. It has been established that no methoxyl groups are present in the tragacanthin fraction, whereas the bassorin fraction comprised approximately 5.38% methoxyl moieties. Rowson (1937) suggested that the gums having higher methoxyl content, that is, possessing higher bassorin contents yielded the most viscous mucilage.

Tragacanth gum is composed mainly of sugars and uronic acid units and can be divided into three types of constituents. The acidic constituents tragacanthic acid on hydrolysis yields galactose, xylose and galacturonic acid. A neutral polysaccharide affords galactose and arabinose after its hydrolysis while a third type is believed to be steroidal glycoside.

Chemical Tests

1.     An aqueous solution of tragacanth on boiling with conc. HCl does not develop a red colour.

2.     It does not produce red colour with ruthenium red solution.

3.     When a solution of tragacanth is boiled with few drops of FeCl₃ [aqueous 10% (w/v)], it produces a deep-yellow precipitate.

4.     It gives a heavy precipitate with lead acetate.

5.     When tragacanth and precipitated copper oxide are made to dissolve in conc. NH₄OH, it yields a meager precipitate.

Uses

It is used as a demulcent in cough and cold preparations and to manage diarrhoea. It is used as an emollient in cosmetics. Tragacanth is used as a thickening, suspending and as an emulsifying agent. It is used along with acacia as a suspending agent. Mucilage of tragacanth is used as a binding agent in the tablets and also as an excipient in the pills. Tragacanth powder is used as an adhesive. It is also used in lotions for external use and also in spermicidal jellies. It is also used as a stabilizer for ice cream in

0.2–0.3% concentration and also in sauces. Tragacanth has been reported to inhibit the growth of cancer cells in vitro and in vivo.

Adulterant and Substitutes

Tragacanth gum of lower grades known as hog tragacanth is used in textile industry and in the manufacture of pickles. The gum varies from yellowish brown to almost black. Citral gum obtained from A. strobiliferus is also used as an adulterant.

Karaya gum which is sometimes known as sterculia gum or Indian tragacanth is invariably used as a substitute for gum tragacanth.

Toxicology

Tragacanth is generally recognized as safe (GRAS) in the United States for food use. There is no indication that dietary supplementation for up to 21 days has any significant adverse effects in man. Tragacanth is highly susceptible to bacterial degradation and preparations contaminated with enterobecteria have been reported to have caused fetal deaths when administered intraperitoneally (i.p.) to preg-nant mice. A cross sensitivity to the asthma-induced effects of quillaja bark has been observed for gum tragacanth.