Rheological and structural study of electrostatic cross-linked xanthan gum hydrogels induced by β-lactoglobulin

This study examines for the first time the role of xanthan gum (XG) and beta -lactoglobulin ( beta lg) in network formation induced by electrostatic attractive interaction. The gelation processes of beta lg-XG mixtures were monitored by viscoelastic measurements as a function of the beta lg-XG ratio and beta lg and XG concentrations. The structural characterization of the gels was addressed by means of confocal laser scanning microscopy. It was found that the initial tenuous network of XG provided a frame for gel organization, the beta lg aggregated along the XG chains and could be regarded as a crosslinking agent, and more elastic gels were obtained at high XG concentrations. The lowest XG concentration at which gelation is possible is estimated to be 4.8 10 super(-3) wt%. The beta lg-XG ratio strongly affects gelation kinetics and is a main factor controlling the gelation process and the gel structure. The optimal ratio for electrostatic interaction at final pH of gels was estimated to be approximately 3.5. The decreasing repulsive interaction between XG chains and the increasing attractive interaction between beta lg and XG with decreasing pH resulted in the formation of soluble complexes followed by the formation of interpolymer complexes. The electrostatic cross-linking of XG chains by beta lg results in a sol-gel transition at the point of gelation. This mechanism may be applicable in a wide variety of protein-polysaccharide systems in which the structure of these systems is mainly stabilized by electrostatic attractive interaction.