Structural characteristics of crosslinking domain in gellan gum gel

Gellan gum samples having different counterions of TMA(+) (tetramethylammonium ion), Na+, K+ and Cs+ were prepared, and the small-angle X-ray scattering was observed from the aqueous solutions of those samples. A sharp peak appears in the SAXS profile at low temperature, indicating the electrostatic interaction between the domains composed of multiple gellan gum chains. The SAXS profile revealed a rigid rod-like characteristics of gellan gum chain. The cross-sectional radius of gyration was evaluated from the scattering profiles, and the gelation mechanism was discussed from the change of the cross-sectional radius of gyration upon gel-sol transition. Taking the difference of the scattering power of counter ions into account, the ion condensation due to gelation was evaluated from the excess scattering of Cs+ gellan gum with respect to K+ gellan gum in respective aqueous solutions.