Concentration-dependent rheological behavior and gelation mechanism of high acyl gellan aqueous solutions

In this study, the rheological properties and gelation mechanism of high acyl gellan (HAG) were investigated. The critical overlap concentration (C^⁎) of HAG was determined to be 0.045%, and the specific viscosity (η_sp) of HAG solutions linearly varied as the concentration of C^1.42 and C^3.51 before and after the concentration, respectively. The transition concentration was found to shift toward a lower value (0.045% vs. 0.08%) when compared with the generality of random coil polysaccharide solutions, indicating the occurrence of intermolecular associations. At sufficiently high concentrations (i.e., above 0.125%), HAG molecules associated with each other to form a heterogeneous three-dimensional network, thus leading to gelation. The gelling temperature depended on HAG concentration, and there was no significant thermal hysteresis observed when heating the formed gels. Furthermore, it was found that acyl substituents allowed HAG molecules to form hydrophobic regions during the gelation process, which was attributed to the intermolecular aggregations driven by hydrophobic interactions. Our findings may deepen the understanding on HAG gelation and thus broaden the application of HAG in the food and biomaterial fields.