Xanthan gum in aqueous solutions: Fundamentals and applications.

Xanthan gum is a naturally occurring polysaccharide obtained from Xanthomonas campestris. The xanthan gum backbone consists of β-d-glucose linked like in cellulose. The trisaccharide β-d-mannose-(1-4)-α-d-glucuronic acid-(1-2)-α-d-mannose is linked to O(3) position of every other glucose residue. Ketal bonds link pyruvic acid residues to approximately half of the terminal mannose residues. The terminal mannose residues also carry acetate groups. Xanthan gum is used as a thickening, stabilizing, or suspending agent in various applications, e.g., food, pharmaceutical, cosmetic, and petroleum extraction. The performance of xanthan gum is based on its macromolecular conformation and association in solution and at interfaces. In water, xanthan gum undergoes conformational transitions from helix to random coil, in response to stimuli such as pH, ionic strength, temperature, and shear. This review presents fundamental information on the behavior of xanthan gum in aqueous media, at conditions and in the presence of additives which are of interest to applications that benefit from viscosity changes such as in oil and gas extraction. Effects on xanthan gum aqueous solutions of pH, electrolytes, changes in temperature, and added natural polysaccharides or synthetic polymers are highlighted. Such information is useful in the formulation of products and the design of processes involving xanthan gum and related polysaccharide polymers.