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xantan gum overview |
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Xanthan gum is a polysaccharide used as a food additive and rheology modifier.(Davidson ch. 24) It is produced by a process involving fermentation of glucose or sucrose by the Xanthomonas campestris bacterium.
Chemical structure
The backbone of the polysaccharide chain consists of two β-D-glucose units linked through the 1 and 4 positions. The side chain consists of two mannose and one glucuronic acid, so the chain consists of repeating modules of five sugar units. The side chain is linked to every other glucose of the backbone at the 3 position. About half of the terminal mannose units have a pyruvic acid group linked as a ketal to its 4 and 6 positions. The other mannose unit has an acetyl group at the 6 positions. Two of these chains may be aligned to form a double helix, giving a rather rigid rod configuration that accounts for its high efficiency as a viscosifier of water. The molecular weight of xanthan varies from about one million to 50 million depending upon how it is prepared.
History
It was discovered by an extensive research effort by Allene Rosalind Jeanes and her research team at the United States Department of Agriculture, which involved the screening of a large number of biopolymers for their potential uses. It was brought into commercial production by the Kelco Company under the trade name Kelzan in the early 1960's. (Whistler p. 486) It was approved for use in foods after extensive animal testing for toxicity in 1969. It is accepted as a safe food additive in the USA, Canada and Europe, with E number E415.
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