Acacia Gum

ACACIA GUM

Synonyms

Acacia gum, Acacia vera, Egyptian thorn, Gummi africanum, Gum Senegal, Gummae mimosae, Kher, Sudan gum arabic, Somali gum, Yellow thorn, Indian Gum and Gum Arabic.

Biological Source

According to the USP, acacia is the dried gummy exuda-tion obtained from the stems and branches of Acacia senegal (L.) Willd or other African species of Acacia. In India, it is found as dried gummy exudation obtained from the stems and branches of Acacia arabica Willd, belonging to family Leguminosae

Geographical Source

Acacia senegal is the characteristic species in the drier parts of Anglo-Egyptian Sudan and the northern Sahara, and is to be found throughout the vast area from Senegal to the Red Sea and to eastern India. It extends southwards to northern Nigeria, Uganda, Kenya, Tanzania and southern Africa. The plant is extensively found in Arabia, Kordofan (North-East Africa), Sri Lanka and Morocco. In India it is found chiefly in Punjab, Rajasthan and Western Ghats. Sudan is the major producer of this gum and caters for about 85% of the world supply.

Cultivation and Collection

Acacia is a thorny tree up to 6 m in height. In Sudan, gum is tapped from specially cultivated trees while in Senegam-bia, because of extremes of climate; cracks are produced on the tree and the gum exudes and is collected from the wild plants. Acacia trees can be cultivated by sowing the seeds in the poor, exhausted soil containing no minerals. The trees also grow as such by seed-dispersal.

Gum is collected by natives from 6 to 8 years old trees, twice a year in dry weather in November or in February— March. Natives cut the lower thorny branches to facilitate the working and by means of an axe make 2–3 ft long and 2–3 inches broad incision on the stem and branches, loosen the bark by axe and remove it, taking care not to injure the cambium and xylem. Usually they leave a thin layer of bark on xylem. If xylem is exposed, white ant enters the plant and gum is not produced. After injury in winter gum exudes after 6–8 weeks while in summer after 3–4 weeks. It is believed that bacteria finding their way through the incision are more active in summer and gum is produced quickly. The exuded gum is scraped off, collected in leather bags and then is cleaned by separating debris of bark and wood and separating sand, etc., by sieving.

Gum is dried in the sun by keeping it in trays in thin layers for about 3 weeks when bleaching takes place and it becomes whiter. This result in uneven contraction and cracks and fissures are formed on its outer surface and as a result original transparent gum becomes opaque. This process is called ripening of the gum.

Morphology

                             Acacia senegal

History

Gum was brought from the Gulf of Aden to Egypt in the 17th B.C., and in the works of Theophrastus it is spoken of as a product of Upper Egypt. The West African product was imported by the Portuguese in the fifteenth century. Until quite recently, commerce in the Sudan was in the hands of a number of local merchants, but it is now entirely controlled by the Gum Arabic Company Ltd., a concessional company set up by the Sudanese Government. This Company alone produces about 40,000 tonnes per annum.

Chemical constituents

Acacia consists principally of arabin, which is a complex mixture of calcium, magnesium and potassium salts of arabic acid. Arabic acid is a branched polysaccharide that yields L-arabinose, D-galactose, D-glucuronic acid and L-rhamnose on hydrolysis. 1, 3-Linked D-galactopyranose units form the backbone chain of the molecule and the terminal residues of the 1, 6-linked side chains are primarily uronic acids. Acacia contains 12–15% of water and several occluded enzymes such as oxidases, peroxidases and pectinases. The total ash content should be in the range of 2.7–4.0%.

Chemical Tests

1.     Lead acetate test: An aqueous solution of acacia when treated with lead acetate solution yields a heavy white precipitate.

2.     Reducing sugars test: Hydrolysis of an aqueous solution of acacia with dilute HC1 yields reducing sugars whose presence are ascertained by boiling with Fehling’s solution to give a brick-red precipitate of cuprous oxide.

3.     Blue colouration due to enzyme: When the aqueous solution of acacia is treated with benzidine in alcohol together with a few drops of hydrogen peroxide (H₂O₂), it gives rise to a distinct blue colour due to the presence of oxidases enzyme.

4.     Borax test: An aqueous solution of acacia affords a stiff translucent mass on treatment with borax.

5.     Specific test: A 10% aqueous solution of acacia fails to produce any precipitate with dilute solution of lead acetate (a clear distinction from Agar and Tragacanth); it does not give any colour change with Iodine solution (a marked distinction from starch and dextrin); and it never produces a bluish-black colour with FeCl₃ solution (an apparent distinction from tannins).

Uses

The mucilage of acacia is employed as a demulcent. It is used extensively as a vital pharmaceutical aid for emulsification and to serve as a thickening agent. It finds its enormous application as a binding agent for tablets, for example, cough lozenges. It is used in the process of ‘granulation’ for the manufacturing of tablets. It is considered to be the gum of choice by virtue of the fact that it is quite com-patible with other plant hydrocolloids as well as starches, carbohydrates and proteins. It is used in combination with gelatin to form conservates for micro-encapsulation of drugs. It is employed as colloidal stabilizer. It is used extensively in making of candy and other food products. Gum acacia solution has consistency similar to blood and is administered intravenously in haemodialysis. It is used in the manufacture of adhesives and ink, and as a binding medium for marbling colours.

Allied Drugs

Talka gum is usually much broken and of very variable composition, some of the tears being almost colourless and others brown.

Ghatti or Indian gum is derived from Anogeissus latifolia (Combretaceae). It is produced in much the same localities as sterculia gum, and is harvested and prepared in a similar manner. It resembles talka in possessing tears of various colours. Some of the tears are vermiform in shape and their surface shows fewer cracks than even the natural acacia. Aqueous dispersions of the gum have a viscosity intermedi-ate between those of acacia and sterculia gums.

West African Gum Combretum, obtained from Com-bretum nigricans, is not permitted as a food additive but is exploited as an adulterant of gum arabic. Unlike the latter in which the rhamnose and uronic acid units are chain terminal, in gum combretum these moieties are located within the polysaccharides chain.

Many other gums of the acacia type are occasionally met with in commerce, and many gum exudates of the large genus Acacia have been given chemotaxonomic con-sideration.

Toxicology

Acacia is essentially nontoxic when ingested. Allergic reac-tions to the gum and powdered forms of acacia have been reported and include respiratory problems and skin lesions.

Acacia contains a peroxidase enzyme, which is typically destroyed by brief exposure to heat. If not inactivated, this enzyme forms coloured complexes with certain amines and phenols and enhances the destruction of many pharmaceutical products including alkaloids and readily oxidizable compounds, such as some vitamins. Acacia gum reduces the antibacterial effectiveness of the preservative methyl-p-hydroxybenzoate against Pseudomonas aeruginosa presumably by offering physical barrier protection to the microbial cells from the action of the preservative. A trypsin inhibitor also has been identified, but the clinical significance of the presence of this enzyme is not known.

Marketed Product

Dental cream and Evecare syrup and capsule manufactured by Himalaya Drug Company.