Gum Arabic

Introduction

Source
The oldest and best-known of all natural gums is Gum Arabic, also known as Gum Acacia, Turkey Gum, Gum Senegal and by many other descriptive and colorful local names. Gum Arabic is the dried, gummy exudation obtained from various species of Acacia trees of the Leguminosae family. About 500 species of Acacia are distributed over tropical and sub-tropical areas of Africa, India, Australia, Central America and south-west North America, but only a comparatively few are commercially important. The important producing areas are the Republic of the Sudan, French West-Africa and several smaller neighboring African countries.

Properties

General
Gum Arabic is unique amoung the natural hydrocolloids because of its extremely high solubility in water. Most common gums cannot be dissolved in water at concentrations higher than about 5% because of their very high viscosities. Gum Arabic, however, can yield solutions of up to 50% concentration. At these high levels, it can actually form a highly viscous, gel-like mass similar in character to a strong starch gel. In addition to forming high-solids gels of this type, Gum Arabic can be used at much lower concentrations in combination with other gums as thickeners and binders. Gum Arabic is insoluble in oils and in most organic solvents. It is soluble an aqueous ethanol up to a limit of about 60% ethanol. Limited solubility can also be obtained with glycerol and ethylene glycol. Whereas most gums form highly viscous solutions at low concentrations of about 1-5%, Gum Arabic is unique in that it is extremely soluble and is not very viscous at low concentrations. High viscosities are not obtained with Gum Arabic until concentrations of about 40-50% are obtained. This ability to form highly concentrated solutions is responsible for the excellent stabilizing and emulsifying properties of Gum Arabic when incorporated with large amounts of insoluble matters. The viscosity of Gum Arabic solutions will depend upon the type and variety of Arabic used. At concentrations up to 40%, Gum Arabic solutions exhibit typical Newtonian behavior. Above 40%, solutions take up pseudoplastic characteristics as denoted by a decrease in viscosity with increasing shearing stress.

Physical Characteristics
Gum Arabic is available in tears, crystals, granules, powder (by mechanical process), spray- and roller-dried powder.

Standards

Minimum standards for good quality Gum Arabic have been defined in the United States Pharmacopeia USP23 and by European Union Specification E-414 as under:

Arsenic (as As): <= 3ppm
Ash (total): <= 4%
Ash (acid insoluble): <= 0.5%
Heavy metals (as Pb): <= 40ppm
Lead: <= 10ppm
Insoluble matter: <= 1%
Loss on drying: <= 15%

No presence of starch, dextrin, or tannin by standard test.

Applications

• Confectionery
  Gum Arabic has been used widely in the confectionery industry. With most confectionery products, Gum Arabic has two important functions - to retard or prevent sugar crystallization and to emulsify the fat and keep it evenly distributed throughout the product. For prevention of sugar crystallization, Gum Arabic finds its greatest application in confections in which sugar content is high and moisture is low, e.g., in jujubes and pastilles. With theses products, the technique of incorporating the flavors is extremely important. Usually, the Gum Arabic is dissolved in water and the solution is filtered, mixed with sugar, and boiled. The flavor is added with a minimum of stirring to prevent formation of bubbles or opaque spots.
  The second function, as a fat emulsifier, is essential to keeping fat distributed uniformly throughout an easily oxidizable, greasy film. This property makes Gum Arabic extremely useful as an emulsifying agent in caramels and toffees.
• Flavors
  The emulsification properties of Gum Arabic are utilized in various liquid flavor emulsions. Many citrus oils and other beverage flavor emulsions utilize the emulsification properties of the Gum. When used as a flavor fixative, the superior filmforming ability of Gum Arabic makes it ideal for protecting the flavor from oxidation, evaporation and absorption of moisture from the air.
• Brewing
  It is used as a foam stabilizer and agent to promote adhesion of foam to glass.
• Pharmaceuticals
  Gum Arabic suspending and stabilizing properties are employed to suspend insoluble drugs and to prevent the precipitation of heavy metals. Its emulsifying property is used for calomine, magnesia, and kaolin suspensions and liquid petrolatum and cod liver emulsions. Many cough drops and syrups utilize Gum Arabic because of its demulcent of soothing characteristics. Gum Arabic is used as an adhesive and binder for pharmaceutical tablets as well as in their coating.
• Cosmetics
  As a protective colloid, Gum Arabic is used in creams, lotions, mascaras and cake cosmetics.
• Lithography
  In lithography, Gum Arabic is used as a sensitizer for lithographic plates as an element in the light sensitive composition and as an ingredient of the fountain solution.
• Inks
  Gum Arabic is an important constituent of many special purpose inks. Water color and quick drying inks utilize the suspending and binding properties of Gum Arabic.
• Textiles
  Gum Arabic gives body in finishing silk and rayon fabric without loss of transparency. It is also used as a sizing and finishing agent in printing formulations for imparting designs or decorations to fabrics.

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