Flocculation of food dispersions by gums: isotropic/anisotropic dispersion separation by xanthan gum

Abstract

Creaming (flocculation) of a model food dispersion in the presence of xanthan and guar gums was studied using phase separation measurements, back-light scattering studies and microscopic observations. Xanthan gum was a much more effective flocculent than guar gum, especially at lower gum concentrations. Dispersion separation with xanthan gum also showed interesting features. The degree of separation gradually decreased with decreasing xanthan gum concentration and creaming could be detected as low as 10 ppm xanthan. Moreover, separation by xanthan gum was non-specific on the nature of the dispersion (fat, silica or latex dispersion) and had a phase separation character: most of the macromolecules migrated out of the flocculated dispersion into the aqueous phase. Based on these observations, it is suggested that the mechanism of dispersion separation by xanthan gum is a geometrical incompatibility between the anisotropic, worm-shaped xanthan molecules and the isotropic dispersed particles. The effects of xanthan gum molecular mass and dispersion concentration were in agreement with the theories on isotropic/anisotropic phase separations.