Isolation and Purification of Microbial Exopolysaccharides and Their Industrial Application

Exopolysaccharide is long-chain high molecular weight polymeric carbohydrates composed of monosaccharide units bound together by glycosidic linkage, which are secreted extracellularly by the secreting microscopic cell or organism. These exopolysaccharides can be either homopolysaccharide or heteropolysaccharide in nature. Exopolysaccharide comprises repeated units of sugar moieties attached to the carrier lipid and can be associated with proteins, lipids, organic and inorganic compounds, and metal ions. Bacteria, archaea, yeast, filamentous fungi, and single cell of eukaryotes produce microbial exopolysaccharides. Microbial synthesis of polysaccharides is greatly influenced by environmental factors such as temperature, pH, pressure, salinity, toxicity, and radiation levels across their ecological niche. Due to the very less production time of exopolysaccharides and its simple purification process, these have found various successful applications in various industrial sectors such as pharmacology, diagnostics, nutraceuticals, functional foods, cosmetics, herbicides and insecticides, bioremediation, biotechnology, petrochemicals, dairy industry, and paint industry. Some of the most important exopolysaccharides and its industrial applications are Acetan (as preservative), Alternan (as commercial gum Arabic), Biodispersion (as remediation of oil spills), Cellulose (as non-indigestible fiber), Curdlan (as a food additive and gelling agent), Dextran (as moisturizers), Emulsan (as crude oil recoveree), Gellan (as stabilizer and microencapsulation matrix), Hyaluronan (as for the removal of dead cells in skincare products), Kefiran (as anti-cancer agents), Levan (as viscosifier), Mutan (as adhesives), Succinoglucan (as emulsion stabilizers), Welan (as thickening agents in high-temperature industries), Xanthan (as an emulsifier and suspending agent), and Pullulan (as orally consumable films). These exopolysaccharides are produced by bacterial species such as Acetobacter, Pseudomonas, Leuconostoc, Alteromonas, Alcaligenes, Lactobacillus, Zymomonas, Xanthomonas, Aureobasidium (fungus). These compounds are purified by techniques such as membrane filtration, dialysis, precipitation, various types of column chromatography, lyophilization, distillation, and rotatory vaporization. This chapter describes different isolation and purification techniques for microbial exopolysaccharides.