194 Chapter 7 Production and applications of microbial exopolysaccharides 7.1 Introduction Commercial applications for polysaccharides include their use as food additives medicines and industrial products. Although plant polysaccharides(such as starch, agar and alginate) have been exploited commercially for many years, microbial exopolysaccharides have only become widely used over the past few decades. The diversity of polysaccharide structure is far greater in micro-organisms compared to plants and around 20 microbial polysaccharides with market potential have been described. However, micro-organisms are still considered to be a rich and as yet underexploited source of exopolysaccharides chapter Successful commercial application of microbial exopolysaccharides depends on overview exploiting their unique physical properties. These properties concern the rheology of exopolysaccharides in solution and their ability to form gels at relative heir concentrations. The physical properties of exopolysaccharides arise largely from gh molecular weight; their molecular confirmations determined by their primary structure;associations between molecules in solution. In this Chapter we will commence by considering the origin, or natural sources of exopolysaccharides, and their molecular composition. We will then consider how the molecular composition determines exopolysaccharide structure and, in turn, how structure determines the unique physical properties of exopolysaccharides. The commercial applications of the unique physical properties of exopolysaccharides will then be discussed. We shall see that microbial exopolysaccharides are widely used as viscosifier and as gelling agents They are, for example, used in the food industry as stabilisers, adhesive, thickening agents and foam stabilisers. Other industrial applications include their use as thickening agents in the printing industry and as gels for improved petroleum recovery in the oil industry. The prospect of those approaching commercial use in food, medical and industrial areas will also be considered. Later in the Chapter, the biosynthesis of exopolysaccharides and, in particular, the genetics and regulation of synthesis will be discussed. Much of our knowledge in this area comes from studies on the bacterium Xanthomonas campestris the industrial producer of the commercially very important exopolysaccharide xanthan Our understanding of the genetics of exopolysaccharide synthesis is advancing rapidly and offers opportunities, not only to improve yields of exopolysaccharides, but also to modify their composition and thus their structure and properties, giving rise to new applications. Finally, we will consider industrial fermentation of microbial exopolysaccharides, including medium formulation and product recovery, particular in relation to xanthan 7.2 Origin and composition Many different types of carbohydrate-containing molecules are located on the surface of microbial cells. Some of these are components of the microbial cell wall limited to certain types of micro-organisms; such as bacterial peptide lipopolysaccharides, echoic acids and yeast mannans. Other polysaccharides glycan,194 Chapter 7 Production and applications of microbial exopolysaccharides 7.1 Introduction Commercial applications for polysaccharides include their use as food additives, medicines and industrial products. Although plant polysaccharides (such as starch, agar and alginate) have been exploited commercially for many years, microbial exopolysaccharides have only become widely used over the past few decades. The diversity of polysaccharide structure is far greater in mimrganisms compared to plants and around 20 microbial polysaccharides with market potential have been described. However, micro-organisms are still considered to be a rich and as yet underexploited source of exopolysaccharides. Successful commercial application of microbial exopolysaccharides depends on exploiting their unique physical properties. These properties concern the rheology of exopolysaccharides in solution and their ability to form gels at relatively low concentrations. The physical properties of exopolysaccharides arise largely from: their high molecular weight; their molecular confirmations determined by their primary structure; associations between molecules in solution. In this Chapter we will commence by considering the origin, or natural sources of exopolysaccharides, and their molecular composition. We will then consider how the molecular composition determines exopolysaccharide structure and, in turn, how structure determines the unique physical properties of exopolysaccharides. The commercial applications of the unique physical properties of exopolysaccharides will then be discussed. We shall see that microbial exopolysaccharides are widely used as viscosifiers and as gelling agents. They are, for example, used in the food industry as stabilisers, adhesive, thickening agents and foam stabilisers. Other industrial applications include their use as thickening agents in the printing industry and as gels for improved petroleum recovery in the oil industry. The prospect of those approaching commercial use in food, medical and industrial areas will also be considered. Later in the Chapter, the biosynthesis of exopolysaccharides and, in particular, the genetics and regulation of synthesis will be discussed. Much of our knowledge in this area comes from studies on the bacterium Xanthomanas campestris the industrial producer of the commercially very important exopolysaccharide xanthan. Our understanding of the genetics of exopolysaccharide synthesis is advancing rapidly and offers opportunities, not only to improve yields of exopolysaccharides, but also to modify their composition and thus their structure and properties, giving rise to new applications. Finally, we will consider industrial fermenta tion of microbial exopolysaccharides, including medium formulation and product recovery, particular in relation to xanthan. market pomtential chapter overview 7.2 Origin and composition Many different types of carbohydrate-containing molecules are located on the surface of microbial cells. Some of these are components of the microbial cell wall and are limited to certain types of micro-organisms; such as bacterial peptidoglycan, lipopolysaccharides, techoic acids and yeast mannans. Other polysaccharides are not