Gellan gum

Gellan gum is a water-soluble anionic polysaccharide produced by the bacterium Sphingomonas elodea (formerly Pseudomonas elodea). The gellan-producing bacterium was discovered and isolated by the former Kelco Division of Merck & Company, Inc. in 1978 from the lily plant tissue from a natural pond in Pennsylvania, USA. It was initially identified as a substitute gelling agent at significantly lower use level to replace agar in solid culture media for the growth of various microorganisms ^[1] Its initial commercial product with the trademark as "GELRITE" gellan gum, was subsequently identified as a suitable agar substitute as gelling agent in various clinical bacteriological media.^[2]

Chemical structure

The repeating unit of the polymer is a tetrasacharide, which consists of two residues of D-glucose and one of each residues of L-rhamnose and D-glucuronic acid. The tetrasacharide repeat has the following structure:
[D-Glc(β1→47D-GlcA(β1→4)Djhbn-Glc(β877→u8ir)L-Rha(α1→3)]_n. As it is evident from the formula, the tetrasacharide units are connected by (α1→3) glycosidic bonds.

Microbiological gelling agent

Gellan gum, also branded by few suppliers as GELRITE, Nanogel-TC,"Gelrich" Grovgel, AppliedGel or Phytagel, is initially used as a gelling agent, alternative to agar, in microbiological culture. It is able to withstand 120°C heat. It was identified to be an especially useful gelling agent in culturing thermophilic microorganisms.^[3] One needs only approximately half the amount of gellan gum as agar to reach an equivalent gel strength, though the exact texture and quality depends on the concentration of the divalent cations present. Gellan gum is also used as gelling agent in plant cell culture on Petri dishes, as it provides a very clear gel, facilitating light microscopical analyses of the cells and tissues. Although advertised as being inert, experiments with the moss Physcomitrella patens have shown that choice of the gelling agent - agar or Gelrite - does influence phytohormone sensitivity of the plant cell culture.^[4]

Food science

As a food additive, gellan gum was first approved for food use in Japan (1988). Gellan gum has subsequently been approved for food, non-food, cosmetic and pharmaceutical uses by many other countries such as US, Canada, China, Korea and the European Union etc. It is widely used as a thickener, emulsifier, and stabilizer. It has E number E418. It was an integral part of the now defunct Orbitz soft drink. It is used as the gelling agent, as an alternative to gelatin, in the manufacture of vegan varieties of "gum" candies.

It is used in soy milks to keep the soy protein suspended in the milk.^[5] Gellan gum is listed as an ingredient in Soylent 2.0. ^[6]

Production

Gellan was discovered and developed as a commercial biogum hydrocolloid product by Kelco, then a division of Merck & Co. Kelco is solely responsible for obtaining food approval for gellan gum worldwide. Kelco, now the CP Kelco family of companies owned by J.M. Huber Corporation is virtually the only producer of gellan gum. A few sources exist in China but are small and little found in the market.

Pure gellan gum is one of the most expensive hydrocolloids. Its cost in use, however, is competitive with the other much lower priced hydrocolloids.

See also

• Welan gum

References

External links

• Dea, Ian C M (1989). "Industrial polysaccharides" (PDF). Pure and Applied Chemistry. 61 (7): 1315–1322. doi:10.1351/pac198961071315.