Effect of salts on the rheological properties of concentrated xanthan gum in aqueous and gum arabic-based emulsion systems

Xanthan gum (XG) is widely utilized at high concentrations (≥ 1.0%) as a dysphagia thickener, and understanding its rheological characteristics in both aqueous and emulsion systems is crucial for diversifying dysphagia diets. In addition, salts, which are commonly present in beverages, can alter the rheological properties of XG. Therefore, the present study sought to investigate and compare the impact of salts (NaCl, KCl, and CaCl₂) on the rheological properties of 1.0% XG in aqueous and gum arabic-based emulsion systems. As salt concentration increased, a reduction in intrinsic viscosity was observed in both systems due to the charge screening effect of cations, with the emulsion system exhibiting a lower value. All samples displayed shear-thinning behavior. In the aqueous system, regardless of salt type, elevated salt concentration caused an increase in apparent viscosity and viscoelastic moduli values, accompanied by more pronounced thixotropic behavior. Conversely, in the emulsion system, while viscoelastic moduli values increased, apparent viscosity decreased as the salt concentration increased. Moreover, all emulsions thickened with XG exhibited thixotropic behavior, with minimal variations in the thixotropic area as salt concentration increased. Despite negligible differences between the apparent viscosity and complex viscosity of XG in the aqueous system, the latter surpassed the former in the presence of salt, with the disparity increasing as the salt concentration increased. Conversely, an opposite trend occurred in the emulsion system. These findings underscore the divergent influence of salts on the rheological properties of XG in aqueous and emulsion systems.