Tribo-Rheological Properties of Concentrated Xanthan Gum in Octenyl Succinic Anhydride-Modified Starch-Based Emulsion System

Xanthan gum (XG) is widely used at high concentrations (≥ 1.0%) as a dysphagia thickener. Understanding its tribo-rheological characteristics in both aqueous and emulsion systems is crucial for diversifying dysphagia diets. Thus, in this study, the rheological and tribological properties of 1.0% XG in aqueous and emulsion systems were investigated and compared. The emulsion system was stabilized by octenyl succinic anhydride-modified starch, a common emulsifier in the beverage industry. XG addition significantly improved emulsion stability. In the aqueous system, the conformation of XG was disordered with a high intrinsic viscosity (100 dL/g), while in the emulsion system, it showed a relatively more ordered conformation with a lower intrinsic viscosity (29.9–71.8 dL/g). This conformational difference of XG in both systems resulted in disparities in the rheological and tribological properties. Notably, the apparent viscosity and viscoelastic moduli values of XG were higher in the emulsion system than in the aqueous system, and the emulsion system exhibited lower tan δ values than the aqueous system. This indicates that XG formed a more structured and elastic network with enhanced weak gel-like properties in the OSA starch-based emulsion system. This behavior was attributed to electrostatic repulsion between XG and negatively charged emulsion particles, which likely promoted the formation of junction zones among XG chains in close proximity. Moreover, XG exhibited better lubrication properties in the emulsion system, and the lubrication transition of XG from the boundary to the mixed regime occurred earlier in the emulsion system because of its improved pseudoplasticity and ordered conformation.