Gummi arabicum

Gum arabic

Gum arabic, also known as acacia gum, arabic gum, gum acacia, acacia, Senegal gum and Indian gum, and by other names, is a natural gum consisting of the hardened sap of various species of the acacia tree. Gum arabic is collected from acacia species, predominantly Acacia senegal and Vachellia (Acacia) seyal. The term "gum arabic" does not indicate a particular botanical source. In a few cases so‐called "gum arabic" may not even have been collected from Acacia species, but may originate from Combretum, Albizia or some other genus. The gum is harvested commercially from wild trees, mostly in Sudan (80%) and throughout the Sahel, from Senegal to Somalia—though it is historically cultivated in Arabia and West Asia.

Gum arabic is a complex mixture of glycoproteins and polysaccharides predominantly consisting of arabinose and galactose. It is soluble in water, edible, and used primarily in the food industry as a stabilizer, with EU 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, though less expensive materials compete with it for many of these roles.

Definition

Gum arabic was defined by the 31st Codex Committee for Food Additives, held at The Hague, The Netherlands, from 19–23 March 1999, as the dried exudate from the trunks and branches of Acacia senegal or Vachellia (Acacia) seyal in the family Leguminosae (Fabaceae)”. A 2017 safety re-evaluation by the Panel on Food Additives and Nutrient Sources of the European Food Safety Authority (EFSA) said that the term "gum arabic" does not indicate a particular botanical source; in a few cases so‐called "gum arabic" may not even have been collected from Acacia species.

Usage

Gum arabic's mixture of polysaccharides and glycoproteins gives it the properties of a glue and binder that is edible by humans. Other substances have replaced it where toxicity is not an issue, and 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 syrup and "hard" gummy candies such as gumdrops, marshmallows, and M&M's chocolate candies. For artists, it is the traditional binder in watercolor paint, in photography for gum printing, and it is used as a binder in pyrotechnic compositions. Pharmaceutical drugs and cosmetics also use the gum as a binder, emulsifying agent, and a suspending or viscosity increasing agent. Wine makers have used gum arabic as a wine fining agent.

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, envelopes, and cigarette papers. Lithographic printers employ it to keep the non-image areas of the plate receptive to water. This treatment also helps to stop oxidation of aluminium printing plates in the interval between processing of the plate and its use on a printing press.

Food

Gum arabic is used in the food industry as a stabilizer, emulsifier and thickening agent in icing, fillings, soft candy, chewing gum and other confectionery and to bind the sweeteners and flavorings in soft drinks. A solution of sugar and gum arabic in water, gomme syrup, is sometimes used in cocktails to prevent the sugar from crystallizing and provide a smooth texture.

Gum arabic is a soluble dietary fibre, a complex polysaccharide, primarily indigestible to both humans and animals. It is considered non-toxic and safe for human consumption. There is indication of harmless flatulence in some people taking large doses of 30g or more per day. It is not degraded in the intestine, but fermented in the colon under the influence of microorganisms—it is a prebiotic (as distinct from a probiotic). There is no regulatory or scientific consensus about its caloric value; an upper limit of 2 kcal/g was set for rats, but this is not valid for humans. The US FDA initially set a value of 4 kcal/g for food labelling, but in Europe no value was assigned for soluble dietary fibre. A 1998 review concluded that "based on present scientific knowledge only an arbitrary value can be used for regulatory purposes".[9] In 2008 the FDA sent a letter of no objection in response to an application to reduce the rated caloric value of gum arabic to 1.7 kcal/g.[10]

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.
Gum arabic is used as a binder for watercolor painting because it dissolves easily in water. Pigment of any color is suspended within the acacia gum 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 acacia gum typically does not bind the pigment to the paper surface, but is totally absorbed by deeper layers.

If little water is used, after evaporation the acacia gum functions as a true binder in a paint film, increasing luminosity and helping prevent the colors from lightening. Gum arabic allows more subtle control over washes, because it facilitates the dispersion of the pigment particles. In addition, acacia gum slows evaporation of water, giving slightly longer working time.

The addition of a little gum arabic to watercolor pigment and water allows for easier lifting of pigment from paper and thus can be a useful tool when lifting out color when painting in watercolor.

Ceramics

Gum arabic has a long history as additives to ceramic glazes. It acts as a binder, helping the glaze adhere to the clay before it is fired, thereby minimising damage by handling during the manufacture of the piece. As a secondary effect, it also acts as a deflocculant, increasing the fluidity of the glaze mixture but also making it more likely to sediment out into a hard cake if not used for a while.

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 becomes relatively insoluble in water upon exposure to ultraviolet light. In the final print, the acacia gum permanently binds the pigments onto the paper.

Printmaking

Gum arabic is also used to protect and etch an image in lithographic processes, both from traditional stones and aluminum plates. In lithography, gum by itself may be used to etch very light tones, such as those made with a number five crayon. Phosphoric, nitric or tannic acid is added in varying concentrations to the acacia gum to etch the darker tones up to dark blacks. The etching process creates a gum adsorb layer within the matrix that attracts water, ensuring that the oil based ink does not stick to those areas. Gum is also essential to what is sometimes called paper lithography, printing from an image created by a laser printer or photocopier.

Pyrotechnics

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

Composition

Arabinogalactan is a biopolymer consisting of arabinose and galactose monosaccharides. It is a major component of many plant gums, including gum arabic. 8-5' non cyclic diferulic acid has been identified as covalently linked to carbohydrate moieties of the arabinogalactan-protein fraction.

Production

While gum arabic has been harvested in Arabia, Sudan, and West Asia since antiquity, sub-Saharan acacia gum has a long history as a prized export. The gum exported came from the band of acacia trees that once covered much of the Sahel region: the southern littoral of the Sahara Desert that runs 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 exudations on the bark. Traditionally harvested by seminomadic desert pastoralists in the course of their transhumance cycle, acacia gum remains a main export of several African nations, including Mauritania, Niger, Chad, and Sudan. The hardened exudations are collected in the middle of the rainy season (harvesting usually begins in July), and exported at the start of the dry season (November). 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 the desert locust. Sudan, Chad, and Nigeria, which in 2007 together produced 95% of world exports, have been in discussions to create a producers' cartel.