Production and applications of microbial exopolysaccharides The unique physical properties of microbial exopolysaccharides(considered in Section s molecular 7.7), which determine their commercial importance, arises from their molecular informaton conformation. This, in turn, is determined by the primary structure and from associations between molecules in solution ond angles For most exopolysaccharides their shape is determined by the angle of bonds which governs the relative orientations of adjacent sugar residues in the chain. However, the range of relative orientations of adjacent sugar molecules is limited by stericinteractions between molecules along the chain ∏ Which group substituents influence inter-atomic electrostatic repulsion in a glyc The carbonyl( Coo)group, which carries a full charge, will have the most pronounced effect. Oxygen atoms of hydroxyl groups carry a partial negative charge and, therefore each oth helical Exopolysaccharides in solution have an ordered helical conformation, which may be conformation single, double or triple; forexample, xanthan forms a double or triple helix(Figure 7.3c) These are stabilised by intermolecular hydrogen bonds. The helical conformation makes the exopolysaccharide semirigid and the molecules can move large volumes of solution. These volumes overlap even at low concentrations of exopolysaccharide, giving rise to relatively high viscosities. intermolecular The intermolecular interactions stabilise the helices and greatly influence the properties racbons of exopolysaccharides in solution, ie solubility, viscosity and gel-formation. a strong interaction or good-fit between molecules will lead to insolubility, whereas poor interaction will lead to solubility of exopolysaccharides. The interactions between molecules is influenced by the presence of side-chains. For example, cellulose is insoluble but introduction of a three monosaccharide side- chain into the cellulose chain gives the soluble xanthan. Small changes in the structure of the side-chains can alter the molecular interactions and thus properties of the exopolysaccharide These changes may be brought about by choice of production organism; conditions of fermentation chemical modification(post fermentation); nzymatic modification(post fermentation) 7.4 Medium composition for exopolysaccharide production Many different types of carbon substrate can be converted by micro-organisms to exopolysaccharides, these include · carbohydrates; · amino acidsProduction and applications of microbial exopolysaccharides 201 molecular mformatial bond angles held conformatian inbrmdecular inbractions The unique physical properties of microbial exopolysaccharides (considered in Section 7.7), which determine their commercial importance, arises from their molecular conformation. This, in turn, is determined by the primary structure and from associations between molecules in solution. For most exopolysaccharides their shape is determined by the angle of bonds which governs the relative orientations of adjacent sugar residues in the chain. However, the range of relative orientations of adjacent sugar molecules is limited by steric interactions between molecules along the chain. Which group substituents influence inter-atomic electrostatic repulsion in a n glycosyl chain? The carbonyl (COO-) group, which carries a full charge, will have the most pronounced effect. Oxygen atoms of hydroxyl pups carry a partial negative charge and, therefore, repel each other. Exopolysaccharides in solution have an ordered helical conformation, which may be single, double or triple; for example, xanthan forms a double or triple helix Figure 7.3~). These are stabilised by intermolecular hydrogen bonds. The helical confoxmation makes the exopolysaccharide semirigid and the molecules can move large volumes of solution. These volumes overlap even at low concentrations of exopolysaccharide, giving rise to relatively high viscosities. The intermolecular interactions stabilise the helices and greatly influence the properties of exopolysaccharides in solution, ie solubility, viscosity and gel-formation. A strong interaction or 'good-fit' between molecules will lead to insolubility, whereas poor interaction will lead to solubility of exopolysaccharides. The interactions between molecules is influenced by the presence of side-chains. For example, cellulose is insoluble but introduction of a three monosaccharide side-chain into the cellulose chain gives the soluble xanthan. Small changes in the structure of the side-chains can alter the molecular interactions and thus properties of the exopolysaccharide. These changes may be brought about by: choice of production organism; conditions of fermentation; chemical modification (post fermentation); enzymatic modification (post fermentation). 7.4 Medium composition for exopolysaccharide production Many different types of carbon substrate can be converted by micmrganisms to exopolysaccharides, these include: carbohydrates; a aminoacids;