Characterization of gellan gum in aqueous NaCl solution. Discussion

The characterization of gellan gum in 25 mM NaCl solution at 25.0 and 40.0°C was achieved by using static and dynamic light scattering techniques focusing on the molecular-weight distribution. The molecular weights were 21.7 × 10 4 at 25.0 °C (the ordered state) and 9.47 × 10 4 at 40.0 °C (the disordered state), and the ratio close to 2 supported the scheme of the conformational transition of gellan gum between a double helix and a single-stranded coil. The molecular-weight distribution of the gellan gum sample was examined by the Laplace inversion method of the correlation function obtained by dynamic light scattering and by the wormlike chain model with a persistence length of 98 nm at 25.0 °C and 17 nm at 40.0 °C. The distribution obtained reproduced the molecular properties of gellan gum in 25 mM NaCI reasonably well. The present gellan gum sample has a large polydispersity of molecular weight. The chain stiffness changes greatly with temperature, and the gellan molecule behaves as a stiff chain even in the disordered state of a single-stranded chain. The substantial stiffness in the single-stranded state makes double-helix formation easy.