Bacterial polysaccharides, industrial

Exhaustion, 9 175-176, 196 of a dye, 9 163 Exhaust mix, 10 37—38 Exhaust releases, industrial, 10 67 Exhaust streams, categories of, 10 67-68 Exit span areas, in thermal design, 13 258 Exocellular bacterial polysaccharide, 13 70 Exocellular polysaccharides, 20 573 Exons, 20 824... 

Taylor H. Evans and Harold Hibbert, Bacterial Polysaccharides 203 E. L. Hirst and J. K. N. Jones, The Chemistry of Pectic Materials 235 Emma J. McDonald, The Polyfructosans and Difructose Anhydrides 253 Joseph F. Haskins, Cellulose Ethers of Industrial Significance. 279... 

HA is the most expensive bacterial polysaccharide, a medical grade HA sells at US 40,000-60,000 per kg. The HA industry is worth an estimated US 1000million per year. The first hyaluronan biomedical product, Hyalon, was developed in 1970s. The polymer from Streptococcus epizooticus or related species is identical to HA from the human and animal body. 

Bacterial polysaccharides represent a large variety of polymers biosynthesized by bacteria. Their chemical structures and also their physical properties in solution or in the solid state may vary widely. They often contain uronic acid and then become polyelectrolytes (190). Many new polysaccharides have been developed from bacteria for industrial purposes. Exocellular polysaccharides are produced on a large scale by the usual techniques of microbiology and fermentation. This procedure allows good control of the characteristics of the polymers and allows purification of the polysaccharides more easily than from other natural sources (191-194). Extension of such production also allows reducing the price and extends the range of applications. A good example remains the hyalmonan previously produced by extraction from animal somces but in which some fraction of proteins remained. Bacterial hyaluronan can be prepared in a very pme form (195). 

Details of the chemical structure of bacterial polysaccharides have been given previously (198,199). In the following, the main industrial bacterial polysaccharides (xanthan, succinoglycan, gellan) are described briefly. 

Market opportunities still exist for the introduction of new bacterial polysaccharides as additives. In the food industry the cost for clearance for food use is extremely expensive and there is increasingly the requirement to justify need in addition to safety or superior properties. 

Levan has a backbone of p-(2 6) linked o-fructose and occurs as high molecular weight polysaccharide in microorganisms. It is accessible from sucrose by use of the enzyme levansucrase (sucrose 6-fructosyltransferase (FTF, EC 2.4.1.10)). Either culture broth of bacterial strains like Bacillus or Zymomonas or the cell-free supernatant can be used for the enzymatic reaction with sucrose. The molecular weight and the viscosity of levan depend on the strain used and the reaction conditions [131, 134]. Even though levan has interesting properties, it has never gained extensive industrial use up to now [134]. 

Despite the experimental difficulties in deducing them, the sequences of a very large number of heteropolysaccharides are known from many sources. An area particularly fertile in novel structures is that of the bacterial glycocalyx, the extracellular polysaccharides and lipopolysaccharides on the outside of bacteria, which is under biological selection pressure to be as diverse as possible and thus resist attempts by the bacterium s competitors to dissolve away its protective coat with various enzymes. Those heteropolysaccharides for which there is some information on the relation between structure and properties are, unsurprisingly, those which are important to the human body or have industrial applications, and only these will be covered here. 

There are several kinds of natural biodegradable polymers in addition to bacterial PHAs, such as proteins, nucleic acids and polysaccharides. Among them, particulary important polymers such as industrial materials are polysaccharides, such as starch, cellulose, chitin and chitosan. The solid-state structure and properties of starch and amylose [127], cellulose [128] and chitin... 

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