Effect of the xanthan gum on the rheological properties of alginate hydrogels

Hydrogels are three-dimensional polymeric structures with remarkable physicochemical and mechanical prop-erties. The selection of biopolymers as constituents of hydrogels is of great importance to enable their use in a variety of fields. The present study proposes a mixed hydrogel of alginate and xanthan gum prepared by the in -situ gelation method. Since alginate gelation is induced by calcium crosslinking, two calcium concentrations have been used in this study. In detail, the influence of xanthan gum and calcium cations on the rheological behavior of alginate hydrogels were investigated using steady shear rheology, dynamic and transient shear rheological experiments. The results showed that the hydrogels behaved like a shear-thinning material, as Carreau fluids, and that the overall viscosity of the hydrogel was dependent on both Ca2+ and xanthan gum concentrations. The length of linear viscoelastic range was influenced by xanthan gum content only at low calcium concentration, while the storage modulus (G ') was found to increase with xanthan gum and calcium content. The interpolation of mechanical spectra with a power law demonstrated that G ' and G '' were slightly dependent on the frequency and that G ' became less frequency dependent with the addition of xanthan gum. Even though the elastic contribution of the hydrogel increased with calcium and xanthan concentration, the hydrogels obtained were not able to fully recover their original structure after the application of a high load. The behavior at large amplitude oscillation strain, mimicking real processing conditions, showed that hydrogels crosslinked with a low calcium concentration were affected by xanthan gum even at lower concentrations than hydrogels crosslinked with high calcium content. Such hydrogel mixtures could find application in research in the food industry.