Xanthan 4,6-pyruvate mannose

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. 

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 is an exo-cellular biopolymer produced by bacteria of the Xanthomonas genus. It is composed of glucose, mannose, glucuronic acid, pyruvate and acetate units. Its sugar composition is generally constant, but acetate and pyruvate contents may depend on the strain used 3,4) and on fermentation conditions such as nature and concentration of the carbon source, dissolved oxygen content and other nutrient limitations (5,6). 

The hydroxyl group at the C6 carbon in the first D-mannose group is frequently ace-tylated and the final mannose sugar is frequently derivatized by pyruvic acid. The P-(l,4)-glycosidic bond that connects the P-o-glucose of the xanthan backbone is characteristic of the structural cell wall polysaccharides found in most plants (i.e., cellulose). The backbone is an extended structure in solution comb-like trisaccharide side chains rendered it water-soluble. Xanthan is anionic by virtue of carboxylic acid residues on the D-glucuronic acid and the pyruvic acid moiety on the terminal o-mannose. 

Figure 14 Partial structure of xanthan gum showing P-D-(l,4)-glucose, 10, acetylated P-d-(1,2)-mannose, 11, P-D-(l,4)-glucuronic acid, 12, and pyruvic acid terminated P-D-mannose, 13. 

Xanthan (qv) is an extracellular bacterial polysaccharide produced by Xan-thomonas campestris. Xanthan is a branched polysaccharide with jS-1 4-d-glucopyranose units along the backbone. On every other nnit the oxygen at C-3 is substituted with a trisaccharide imit. Approximately half the fi-D mannose imits have a pyruvic acid group linked as an acetal derivative. Molecular weight has been estimated to be 2 x 10 . 

Xanthan gum can be regarded as a cellulose derivative. The main chain consists of 1,4 linked P-glucopyranose residues. On an average, every second glucose residue bears in the 3-position a trisaccharide of the structure P-D-Man/ -(1 4)-P-d-G1c/ A(1 2)-a-D-Man/7 as the side chain. The mannose bound to the main chain is acetylated in position 6 and ca. 50% of the terminal mannose residues occur ketahzed with pyruvate as 4,6-0-(l-carboxyethylidene)-D-mannopyranose (cf. Formula 4.162 GlcpA glucuronic acid). 

The main xanthan chain consists ofp-D-(l— 4) glucose units that also occur in cellulose. Side chains (usually trisaccharides) consist of a D-glucuronic acid residue and two D-mannose residues (4-180). To the terminal D-mannose unit of the side chain is attached to P-d-glucuronic acid through - (1 4) glycosidic bond. Glucuronic acid is further linked to a-D-mannose by a (1— 2) bond. The structure is further complicated by the presence of pyruvic add linked, as an... 

Xanthan gum is a very long, linear polymer. Its molecular weight has been reported to range from 1 million to 10 million. The molecule consists of a chain composed of D-glucose, D-mannose, and o-glucuronic acid, with short side chains. Pyruvic acid, present in side chains, accounts for 2.5. 8 of the molecule (glicksman whistler and bemiller). Xanthan gum samples with high pyruvate contents have been reported to yield solutions... 

Xanthan Xanthomonas spp. Glucose, Sucrose, Glucose-syrup, Whey D-Glucose, D-Mannose, D-Glucuronic acid, Acetyl Pyruvate... 

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