Modified xanthan—its preparation and viscosity

Abstract

Xanthan with various pyruvic acid and acetate contents has been prepared from a single commercial polysaccharide sample using optimised chemical conditions (acid and alkali hydrolysis, respectively) for removal of acetal and acyl groups. The only significant change found on analysis of the modified xanthans was loss of pyruvic acid and/or acetate; no low moleculur weight carbohydrate-containing material was released. Contrary to some previous reports, evidence is presented to show that the pyruvic acid acetal and o-acetyl contents of xanthan do not affect solution viscosity. The viscosities of native, pyruvate-free and pyruvate/acetate-free xanthan solutions (0·3% w/v) were similar at shear rates 8·8–88·3 s −1 in both distilled water and 1% KCl. Over the concentration range 0·2-1·5%, the viscosities of native and pyruvate-free xanthan at 10 s −1 were similar. The viscosity increase on addition of 1% KCl to salt-free xanthan solutions was independent of pyruvic acid acetal substitution. Our results suggest that xanthan samples with various pyruvic acid acetal and o-acetal contents, prepared under different fermentation conditions of Xanthomonas campestri should not normally be used for assessing the contribution of these groups to solution viscosity.