Gum arabic
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Gum arabic, a natural gum also called gum acacia, is a substance that is taken from two sub-Saharan species of the acacia tree, Acacia senegal and Acacia seyal. It is used primarily in the food industry as a stabilizer, but has had more varied uses in the past, including viscosity control in inks. Its E number is E-414.
The gum produced by the trees in question reseals the plant's bark in the event of damage - a process called gummosis.
Gum arabic is a complex mixture of saccharides and glycoproteins, which gives it one of its most useful properties: it is perfectly edible. Other substances have replaced it in situations where toxicity is not an issue, as the proportions of the various chemicals in gum arabic vary widely and make its reliable performance troublesome. Still, it remains an important ingredient in soft drink syrups, "hard" gummy candies like gumdrops, and in marshmallows. As the name implies, gum arabic is also found in chewing gums, where it acts as one of the many factors that result in the texture of the gum. For artists it is the traditional binder used in watercolor paint, and was used in photography for gum printing. Pharmaceuticals and cosmetics also use the gum, and it is used as a binder in pyrotechnic compositions. It is an important ingredient in shoe polish. It is also used often as a lickable adhesive on postage stamps and cigarette papers. Printers employ it to stop oxidation of aluminum printing plates in the interval between processing of the plate and its use on a printing press.
The substance is grown commercially throughout the Sahel from Senegal and Sudan to Somaliland.
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[edit] Painting and Art
Gum arabic is used as a binder for watercolor painting because it dissolves easily in water. Pigment of any color is suspended within the gum arabic in varying amounts, resulting in watercolor paint. Water acts as a vehicle or a diluent to thin the watercolor paint and helps to transfer the paint to a surface such as paper. When all moisture evaporates, the gum arabic binds the pigment to the paper surface.
[edit] Photography
The historical photography process of gum bichromate photography uses gum arabic to permanently bind pigments on paper. Ammonium or potassium dichromate is mixed with gum arabic and pigment to create a photographic emulsion, sensitive to ultraviolet light.
[edit] Printmaking
Gum arabic is also used to protect and etch an image in lithographic processes. Ink tends to fill into whitespace on photosensitive aluminum plates if they don't receive a layer of gum. In stone lithography the gum etch is used to etch the most subtle gray tones. Phosphoric acid is added in varying concentrations to the gum arabic to etch the darker tones up to dark blacks. Multiple layers of gum are used after the etching process to build up a protective barrier that ensures the ink does not fill into the whitespace of the image being printed.
Gum arabic is found in lemons.
[edit] Terrorist rumors
Oddly, the connection between Sudan and Osama bin Laden brought the otherwise innocuous gum to public consciousness in 2001, as an urban legend arose that bin Laden owned a significant fraction of the gum arabic production in Sudan, and that therefore one should boycott products using it.[1] As a result, some food producers, for instance Snapple, renamed the ingredient to "gum acacia" on their labels.
This story took on somewhat significant proportions, mostly thanks to an article in The Daily Telegraph a few days after the September 11 attacks, which echoed this claim. Eventually the State Department issued a release stating that while Osama bin Laden had once had considerable holdings in Sudanese gum arabic production, he divested himself of these when he was expelled from Sudan in 1996.
[edit] Pyrotechnics
Gum arabic is also used as a water soluble binder in firework composition.
[edit] Effect on surface tension in liquids
Gum arabic reduces the surface tension of liquids, which leads to increased fizzing in carbonated beverages. This is known as a Mentos eruption and can be seen in The Diet Coke & Mentos Challenge video and website.
[edit] External links
- http://www.sbu.ac.uk/water/hyarabic.html
- http://www.cniworld.com (CNI : Colloides Naturels International is the Gum Arabic World Leader)
