Microbial Exopolysaccharides as Alternative Sources of Dietary Fibers with Interesting Functional and Healthy Properties

Traditional polysaccharides obtained from plants may suffer from a lack of reproducibility in their rheological properties, purity, supply and cost. Most of the used plant polysaccharides are chemically modified to improve their characteristics. Microbial exopolysaccharides (EPSs) are principally composed of carbohydrate polymers, and they are produced by many microorganisms including bacteria, yeasts and fungi. Microorganisms can synthesize EPSs and excrete them out of cell either as soluble or insoluble polymers. These EPSs are able not only to protect the microorganisms themselves against desiccation, phage attack, antibiotics or toxic compounds, but also can be applied in several biotechnological applications. In food products they increase the dietary fiber content and can be used as viscosifiers, stabilizers, emulsifiers or gelling agents to improve physical and structural properties of water and oil holding capacity, viscosity, texture, sensory characteristics and shelf-life. EPSs are used as additives in various foods, such as dairy products, jams and jellies, wine and beer, fishery and meat products, icings and glazes, frozen foods and bakery products. Over the past few decades, interest in using microbial EPSs in food processing has been increasing because of main reasons such as easy production, better rheological and stability characteristics, cost effectiveness and supply. Dextran, xanthan, pullulan, curdlan, levan and gellan and alginate are the main examples of industrially important microbial exopolysaccharides. They also play crucial role in conferring beneficial physiological effects on human health, such as the ability to lower pressure and to reduce lipid level in blood. Furthermore, these EPSs exhibit antitumor, immunomodulating, antioxidant and antibacterial properties. The utility of various biopolymers are dependent on their monosaccharide composition, type of linkages present, degree of branching and molecular weight. In the present chapter, an attempt was taken to recapitulate the most important polysaccharides isolated from microorganisms as well as the main methods for microbial exopolysaccharide production, purification and structural characterization. In addition, the functional and healthy benefits of EPSs and their applications in food industry were described.