Page 306 - Pharmacognosy 2 PG303

Pharmacognosy-2 (PG303) Level 2 Clinical Pharmacy-Pharm D

in Central Africa, forming forests of considerable extent. The best gum is produced
near Kordofan from trees specially cultivated and worked for gum.

Collection and Preparation
The trees are kept properly pruned from dead wood and the lowest branches
are removed. The formation of gum is greatly increased by wounding the stems and
is apparently taken place first in the young phloem and cambium. Towards the end
of November and again in February and March the taper visits trees about six or
seven years old and drives the small blade of a long-handled axe just under the bark
of the stem and large branches without injuring the cambium. By twisting the axe
and pulling it back he leaves two ends. One of these he pulls up and the other down
and so removes a strip of bark 0.5-1.0 metre long. About 3-6 weeks afterwards the
gum which forms in tears near the lower end of the wound is collected and the
orchard is picked over every 4-6 days until rain sets in, when the exudation of gum
ceases. Gum is also spontaneously exuded from wild trees, but this is usually rather
darker in color and not so valuable.

Description
Gum Arabic occurs in rounded or ovoid tears, of variable size, usually about
0.5-2 cm in diameter; whitish or yellowish white; opaque from the presence of
numerous small fissures in the outer part of the tears; in consequence of these, they
easily break up into a number of small transparent angular fragments with glistening
vitreous surface; almost odourless; taste, bland and mucilaginous.
Powdered Gum Arabic is white to yellowish white, showing under the
microscope angular particles, traces of or no starch granules, occasional particles of
vegetable tissues, and no mucilaginous cell walls.

Solubility
1 g of Gum Arabic is almost completely soluble in 1 ml of water. It is insoluble
in alcohol 90 %

Tests for Identity
1- An aqueous solution of gum Arabic (1/1) is translucent, viscous, slightly acidic
to litmus paper and not glairy, and when diluted with water and allowed to stand,
no gummy deposit separates.
2- Optical activity: An aqueous solution of gum Arabic (1/10) is slightly
laevorotatory.
3- Test for oxidase enzyme: To an aqueous solution of gum Arabic (1/5), add few
drops of solution of H 2O 2 and few drops of benzidine T.S., shake, and allow to
stand; a deep blue or a greenish-blue colour is slowly formed (c.f. Gum
Tragacanth).

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