Xanthan mannose

Xanthan, although a gum, is derived from the pure culture fermentation of an organism, TCanthomonas campestris. The organism is filtered from the growth medium and the gum recovered by alcohoHc precipitation, followed by drying. It is composed primarily of D-glucose and D-mannose units. 

Xanthan gum is a long-chain polysaccharide composed of the sugars glucose, mannose, and glucuronic acid. The backbone is similar to cellulose, with added side chains of trisaccharides (three sugars in a chain). 

A polysaccharide such as xanthan gum is a chain of sugars. Some familiar polysaccharides are starch and cellulose. The backbone of xanthan gum is similar to cellulose, but the trisaccharide side chains of mannose and glucuronic acid make the molecule rigid, and allow it to form a right-handed helix. These features make it interact with... 

Xanthan (Figure 11) is a commercially important polysaccharide produced by the bacterium Xanthomonas campestris.187 188 The xanthan backbone consists of a P(l-4)-linked D-glucopyranose chain with a trisaccharide side chain attached at C3 to alternate glucose residues. These side chains consist of an acetylated mannose residue, a glucuronic acid residue, and a pyruvate ketal linked to a terminal mannose residue. The acetate and pyruvate content depend on the fermentation and isolation conditions used by the supplier. 

Bacteria form and secrete a variety of heteropolysaccharides, several of which are of commercial value because of their useful gelling properties. Xanthan gum (formed by Xanthomonas campestris) has the basic cellulose structure but every second glucose residue carries an a-l,3-linked trisaccharide consisting of 6-0-acetylmannose, glucuronic acid, and mannose in the following repeating unit 131132... 

Figure 3. The pentasaccharide repeating unit of xanthan showing the atom labeling. The unlettered residue and residue A are fi-D-glucose B is a-D-mannose C is fi-D-glucuronate and D is 4,6-0-(l-carboxyethyl)-[ -D-mannose.

Xanthan Gum occurs as a cream colored powder. It is a high-molecular-weight polysaccharide gum produced by a pure-culture fermentation of a carbohydrate with Xanthomonas campestris, purified by recovery with isopropyl alcohol, dried, and milled. It contains D-glucose and D-mannose as the dominant hexose units, along with D-glucuronic acid and pyruvic acid, and it is prepared as the sodium, potassium, or calcium salt. It is readily soluble in hot or cold water, but it is insoluble in alcohol. Its solutions are neutral. 

Fig. 35.—Agar diffusion of xanthan antibodies (Ab) and chemically modified xanthan and inhibitors. A xanthan (well 1) reduced xanthan (well 2) oxidized xanthan (well 3) deacety-lated xanthan (well 4) enzymatically treated xanthan (well 5). B Xanthan with 6% pyruvate (well 1), xanthan with 4% pyruvate (well 2), xanthan with 2.8% pyruvate (well 3), xanthan with 0.5% pyruvate (well 4), and xanthan with 0.2% pyruvate (well 5). C, D, E Inhibition of anti-xanthan antibodies by glucuronic acid and mannose wells 1-6 contain decreasing concentrations of xanthan (1-0.3%) solutions of xanthan In antibody + glucuronic acid, In2 antibody + mannose. (Reprinted from Carbohydrate Polymers, Volume 27, J. H. Pazur, F. J. Miskiel, and N. T. Marchetti, pp. 85-91, copyright 1995, with permission from Elsevier Science Ltd., The Boulevard, Langford Lane, Kidlington, 0X5 1GB, UK.)...

Xanthan Made primarily of linear glucose chain with side chains based on mannose and glucuronic acid residues A microbial gum made by glucose fermentation, forms viscous pseudoplastic solutions Emulsifying or suspending agent, particularly in toothpaste and ointments... 

The USPNF 23 describes xanthan gum as a high molecular weight polysaccharide gum. It contains D-glucose and D-mannose as the dominant hexose units, along with D-glucuronic acid, and is prepared as the sodium, potassium, or calcium salt. 

Xanthan, the best studied of the exopolysaccharides, provides a good example of the complexity and specificity of enzymatic attack. Xanthan has a P-l,4-glucosidic (Glu) backbone containing branch points at the 3-positions of every fourth unit. The branches are trisaccharides with a-1,2-mannose acetate, P-l,4-glucuronic acid and P-mannoside (Man) units. Each of the different main chain, branch and side chain bonds can be hydrolyzed by only a specific enzyme, as illustrated below ... 

---