Xanthan gum is an extracellular polysaccharide produced by the bacterium Xanthomonas campestris, widely used as a rheology control agent due to its pseudoplastic behavior and stable viscous properties in aqueous solutions.
Molecular Structure
Xanthan gum consists of a linear backbone of β-(1→4)-D-glucose residues identical to cellulose, with every other glucose unit bearing a trisaccharide side chain composed of β-D-mannose-(1→4)-β-D-glucuronic acid-(1→2)-α-D-mannose at the O-3 position. The inner mannose residue often carries an acetyl group at C-6, while the terminal mannose may contain a pyruvic acid ketal at the C-4/C-6 positions.
This structural organization results in an approximate 2:2:1 ratio of glucose, mannose, and glucuronic acid, with molecular weights ranging from 2 to 20 million Da. The unique architecture promotes the formation of a rigid, ordered helical conformation stabilized by hydrogen bonding, which can transition to disordered coil structures upon heating.
Production and Properties
Xanthan gum is produced through aerobic fermentation of glucose or sucrose by X. campestris at pH 6–7 and temperatures between 28–30 °C. Following fermentation, the polysaccharide is recovered via alcohol precipitation, followed by drying and milling to obtain the final product.
The polymer exhibits high solubility in water irrespective of temperature or ionic strength, pronounced shear-thinning (pseudoplastic) viscosity, thermal and pH stability across a wide range (pH 2–12), and strong salt tolerance. Xanthan gum is also compatible with galactomannans such as guar gum, displaying synergistic viscosity enhancement and gelation. Although generally stable, it can undergo slow enzymatic degradation by xanthanase. These properties arise from the formation of weak network structures through double-helix aggregation.
Biomedical and Pharmaceutical Applications
In pharmaceutical formulations, xanthan gum is widely used as a suspending agent, tablet binder, and controlled-release matrix. Its mucoadhesive properties and non-irritant nature enhance drug bioavailability in oral suspensions and ophthalmic formulations. Xanthan gum is also incorporated into wound dressings to promote moisture retention and is used as a viscosifying agent in injectable preparations.
Its low immunogenicity and excellent biocompatibility contribute to its Generally Recognized as Safe (GRAS) status, supporting its extensive use in biomedical and pharmaceutical applications.
