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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