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3 Microbial Gums: Current Trends and Applications
Rwivoo Baruah and Prakash M. Halami
Microbiology & Fermentation Technology Department, CSIR-Central Food Technological Research Institute, Mysuru, Karnataka, India
3.1 Introduction
Microbial gums are polysaccharides produced by various microbes like bacteria, fungi, and algae as a metabolite. These microbial gums protect their producers from harsh environmental conditions and sometimes act as secondary carbon sources. These gums have a unique property to form a gel when in contact with water. They are used in several industrial applications. Applications of microbial gums are seen in biotechnology, food, cosmetics, environmental and biomedical uses and, in recent times, have seen tremendous progress in this field of research, such as improving microbial gum behavior by chemical modifications or enhancing microbial gum production by bioprocess engineering techniques. Another reason for the increasing interest in microbial gums is due to the fact that they are biodegradable in nature as opposed to synthetic polymeric gums. Compared to plant‐based gums, microbial gums can be produced in large quantities in less time by controlled fermentation [1].
Microbial gums are complex polysaccharides composed of a chain of monosaccharide units joined by glycosidic linkages having high molecular weight. These gums can be classified on the basis of their monomer composition into (i) homopolysaccharides (HoPS) and (ii) heteropolysaccharides (HePS). HoPS are polysaccharides, which are composed of a single type of monomer units like dextran, levan, and pullulan. HePS are polysaccharides, which are composed of more than one type of monomer unit and sometimes composed of noncarbohydrate groups. Microbial gums can be produced as extracellular metabolites such as exopolysaccharide (EPS) or as endo‐polysaccharides [2].
A class of microbial gums originating from Sphingomonas spp., which includes gellan, welan, and diutan, are collectively called sphingans. They have a fairly similar structure but a few different properties [3]. These polysaccharides, even in small concentrations, can increase the viscosity in a solution. These properties are due to the unique composition, linkages among residues, and molecular weight found in different microbial gums from a wide range of bacteria, fungi, and algae [4].
The viscosifying effects of microbial gums, which are nontoxic in nature, have been especially exploited in the food industry as hydrocolloids, emulsifiers, and stabilizers.
This chapter focuses on various aspects of microbial gums like their biosynthesis, production, structure, and functional properties. In this chapter important examples of microbial gums like xanthan, gellan, and pullulan have been highlighted. Further, various applications of microbial gums in food, cosmetics, medical, and nanotechnology have been discussed.
3.2 Biosynthesis of Microbial Gums
Microbial gums are produced in two different ways: (i) extracellularly by means of glycosyltransferase enzymes secreted from the microbial cells, or (ii) intracellularly, where a cascade of enzymes produced
