Comparative heterogeneity, molecular weights and viscosities of xanthans of different pyruvate and acetate content

The bacterial exopolysaccharide xanthan is a well-known hydrocolloid, with a high viscosity deriving from its large molecular weight and volume. Four different xanthans deriving from Xanthomanas campestris – two with similar pyruvate and acetate contents and two with different contents – were characterized in dilute aqueous buffered solution (pH 7.0, ionic strength 0.3 M) using sedimentation velocity and sedimentation equilibrium in the analytical ultracentrifuge, supplemented by dynamic light scattering. This facilitated a comparison with regards heterogeneity (sedimentation coefficient distribution) and molecular weight, despite their large size and low critical overlap concentration. The xanthans were also compared with regard to reduced specific and intrinsic viscosity behaviour. The xanthans generally show strong similarity in properties with the exception of the lowest pyruvate xanthan, a finding which should be useful for future applications of these materials.