Solute Energetics in Aqueous Xanthan Gum Solutions: What Can Be Learned from a Fluorescent Probe?

Abstract

Xanthan gum (XG) is a well-known anionic polysaccharide that finds broad application in the food and petroleum industries because of its ability to enhance solution viscosity at low concentrations and moderate temperatures. The aim of this work was to use the solvation probe coumarin 153 (C153) to characterize changes in the xanthan gum (XG) solution microstructure as a function of XG concentration and temperature from the perspective of a dissolved solute molecule. We established the utility of C153 fluorescence to track solution changes for XG concentrations that span the transition region from a dilute to a semi-dilute solution, defined by the xanthan gum overlap concentration, C*~0.02 g/dL. The temperature was varied from 293 to 353 K to probe solution conditions wherein XG has been reported to undergo a structural change from helix to random coil conformation, the details of which are still under debate. While C153 fluorescence does not elucidate direct structural information, the emission response is a simple means by which changes in aqueous XG solution can be identified. C153 spectroscopy is observed to correlate with XG conformational changes, as reported in the literature.