The rheological behavior, particle properties and supramolecular structure of low acyl gellan gum fluid gels: impact of the calcium concentration before fluid gel formation

Fluid gels are jammed microgel suspensions obtained by shearing a gelling hydrocolloid during its sol-gel transition. This study focused on calcium-induced low acyl gellan gum (LAGG) fluid gels and investigated the impact of calcium concentration before fluid gel formation on the resulting rheological behavior, fluid gel particle properties, and supramolecular structure. The elasticity and yield stress of fluid gels and quiescently cooled gels reached a maximum when the calcium concentration was increased from 0.78 to (approx.) 30 mmol/kg. Small angle X-ray scattering (SAXS) of fluid gels revealed a progressive increase in gel network connectivity up to the calcium concentration where the peak in rheological properties was observed followed by a less interconnected network at calcium concentrations above the peak. Furthermore, rheological measurements supplemented with free calcium and zeta-potential measurements, support that the decrease after the peak in rheological response is due to the combination of fluid gel particle softening with a decrease in surface charge. The results of this study enable to establish clearer links between rheological behavior, particle properties and supramolecular structure of calcium-induced LAGG fluid gels. This work enables a more effective design of fluid gel properties for different applications from food to pharma and biomaterials.