gum arabic

The Acacia senegal, pictured in a medicinal handbook: Franz Eugen Köhler, Köhler's Medizinal-Pflanzen (1887).

Gum arabic, also known as gum acacia, chaar gund, char goond or meska, is a natural gum made of hardened sap taken from two species of the acacia tree; Acacia senegal and Acacia seyal. The gum is harvested commercially from wild trees throughout the Sahel from Senegal and Sudan to Somalia, although it has been historically cultivated in Arabia and West Asia. Gum arabic is a complex mixture of polysaccharides and glycoproteins that is used primarily in the food industry as a stabilizer. It is edible and has E number E414. Gum arabic is a key ingredient in traditional lithography and is used in printing, paint production, glue, cosmetics and various industrial applications, including viscosity control in inks and in textile industries, although cheaper materials compete with it for many of these roles.

Usage

Gum arabic's mixture of saccharides and glycoproteins gives it the properties of a glue, and binder which is edible by humans. 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 it unpredictable. Still, it remains an important ingredient in soft drink syrups, "hard" gummy candies such as gumdrops, marshmallows and M & M's chocolate candies. For artists it is the traditional binder used in watercolor paint, in photography for gum printing, and it is used as a binder in pyrotechnic compositions. It has been investigated for use in intestinal dialysis. Pharmaceuticals and cosmetics also use the gum as a binder, emulsifying agent and a suspending or viscosity increasing agent.^[1]

It is an important ingredient in shoe polish, and can be used in making homemade incense cones. It is also used as a lickable adhesive, for example on postage stamps and cigarette papers. Printers employ it to stop oxidation of aluminium printing plates in the interval between processing of the plate and its use on a printing press^{[citation needed]}.

Painting and art

Powdered gum arabic for artists. One part gum arabic is dissolved in four parts distilled water to make a liquid suitable for adding to pigments.

A selection of Gouaches containing gum arabic.

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.

Photography

The historical photography process of gum bichromate photography uses gum arabic mixed with ammonium or potassium dichromate and pigment to create a coloured photographic emulsion that is sensitive to ultraviolet light. In the final print, the gum arabic permanently binds the pigments onto the paper.

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 do not receive a layer of gum. In 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.

Pyrotechnics

Gum arabic is also used as a water soluble binder in firework composition.

Chemical properties

Effect on surface tension in liquids

Gum arabic reduces the surface tension of liquids, which leads to increased fizzing in carbonated beverages. This can be exploited in what is known as a Diet Coke and Mentos eruption.

Production

Acacia senegal from Paul Hermann Wilhelm Taubert's Leguminosae. in Engelmann (ed.): Natürliche Pflanzenfamilien. Vol. III, 3., 1891

Acacia seyal from Paul Hermann Wilhelm Taubert's Leguminosae. in Engelmann (ed.): Natürliche Pflanzenfamilien. Vol. III, 3., 1891

While gum arabic has been harvested in Arabia, Egypt, and West Asia since antiquity, sub-Saharan gum arabic has a long history as a prized export. The gum exported came from the band of Acacia trees which once covered much of the Sahel region: the southern littoral of the Sahara Desert running from the Atlantic to the Red Sea. Today the main populations of gum producing Acacia species are harvested in Mauritania, Senegal, Mali, Burkina Faso, Niger, Nigeria, Chad, Cameroon, Sudan, Eritrea, Somalia, Ethiopia, Kenya and Tanzania. Acacia senegal is tapped for gum by cutting holes in the bark, from which a product called Kordofan or Senegal gum is exuded. Seyal gum, from Acacia seyal, the species more prevalent in East Africa, is collected from naturally occurring extrusions on the bark. Traditionally harvested by semi-nomadic desert pastoralists in the course of their transhumance cycle, gum arabic remains a main export of several African nations, including Mauritania, Niger, Chad, and Sudan. The hardened extrusions are collected in the middle of the rainy season (harvesting usually begins in July), and exported at the start of the dry season (November). The primary export agent for these nations continues to be a French company, Colloïdes Naturels International, founded during the colonial period to process the gum, which maintains large processing facilities in Nigeria and Rouen, France.^[2] Total world gum arabic exports are today (2008) estimated at 60,000 tonnes, having recovered from 1987–1989 and 2003–2005 crises caused by the destruction of trees by Desert locust. Sudan, Chad, and Nigeria, which in 2007 together produced 95 percent of world exports, have been in discussions to create a producer's cartel.^[3]

Political aspects

Senegambia

In 1445, Prince Henry the Navigator set up a trading post on Arguin island (off the coast of modern Mauritania), which acquired gum arabic and slaves for Portugal. With the merger of the Portuguese and Spanish crowns in 1580, the Spaniards became the dominant influence along the coast. In 1638, however, they were replaced by the Dutch, who were the first to begin exploiting the gum arabic trade. Produced by the acacia trees of Trarza and Brakna and used in textile pattern printing, this gum arabic was considered superior to that previously obtained in Arabia. By 1678 the French had driven out the Dutch and established a permanent settlement at Saint Louis at the mouth of the Senegal River, where the French Company of the Senegal River (Compagnie Française du Sénégal) had been trading for more than fifty years.^[4]

Moorish tribes meet to trade gum arabic at Bakel on the Senegal river, 1890. (illustration from "Côte occidentale d'Afrique du Colonel Frey", pl. en reg. p. 100)

For much of the 19th century, gum arabic was the major export from French and British trading colonies in modern Senegal and Mauritania. France in particular first came into conflict with inland African states over the supply of the commodity, providing an early spur for the conquest of French West Africa. As the Atlantic slave trade weakened in the early 19th century, The Emirate of Trarza and its neighbors in what is today southern Mauritania collected taxes on trade, especially gum arabic, which the French were purchasing in ever-increasing quantities for its use in industrial fabric production. West Africa had become the sole supplier of world gum arabic by the 18th century, and its export at the French colony of Saint-Louis doubled in the decade of 1830 alone. Taxes, and a threat to bypass Saint-Louis by sending gum to the British traders at Portendick, eventually brought the Emirate of Trarza into direct conflict with the French. In the 1820s, the French launched the Franco-Trarzan War of 1825. The new emir, Muhammad al Habib, had signed an agreement with the Waalo Kingdom, directly to the south of the river. In return for an end to raids in Waalo territory, the Emir took the heiress of Waalo as a bride. The prospect that Trarza might inherit control of both banks of the Senegal struck at the security of French traders, and the French responded by sending a large expeditionary force that crushed Muhammad's army. The war incited the French to expand to the north of the Senegal River for the fist time, heralding French direct involvement in the interior of West Africa.^[5] Gum arabic continued to be exported in large quantities from the Sahel areas of French West Africa (modern Senegal, Mauritania, Mali, Burkina Faso, and Niger) and French Equatorial Africa (modern Chad) until these nations gained their independence in 1959-61.

Sudan

Although from the 1950s to the early 1990s Sudan accounted for roughly 80 percent of gum arabic production, today that figure is under 50 percent. ^[6] Hundreds of thousands of poor Sudanese are dependent on gum arabic for their livelihood. However it is still the world's largest single producer, and the production of gum arabic is heavily controlled by the Sudanese government.^[7]

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.^[8] As a result, some food producers, such as 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.^[9]

In a press conference held at the Washington Press Club on 30 May 2007, John Ukec Lueth Ukec, Sudan's ambassador to the United States, threatened to stop exportation of gum arabic from his country if sanctions were imposed. The sanctions proposed by the United States were a political response from the United States to the alleged connection between the government of Sudan and the Janjaweed militia group. Ukec made his speech surrounded by Coca-Cola products, although other sodas use gum arabic as an emulsifier as well.^[10]

John Ukec Lueth Ukec was quoted at the Washington press conference, "I want you to know that the gum arabic which runs all the soft drinks all over the world, including the United States, mainly 80 percent is imported from my country," which he said after raising a bottle of Coca-Cola. According to the Washington Post, a reporter then asked if Sudan was threatening to "stop the export of gum arabic and bring down the Western world." To which Ukec replied, "I can stop that gum arabic and all of us will have lost this," and gestured to the Coke bottle.^[10]

References

External links

• http://www.cniworld.com (Colloïdes Naturels International)
• http://www.helpforibs.com/shop/suplmts/acacia.asp (Dietary acacia fiber)
• http://www.npr.org/templates/story/story.php?storyId=11224050 (NPR story on gum arabic, its production, and use in industry)