Pre-gel solution properties of gellan polysaccharides: Effect of potassium and calcium ions on chain associations

The effect of added ions (0.5 mM K+ or 0.25 mM Ca2+) and temperature (25 or 60 °C) on the solution properties of gellan polysaccharides (0.15% w/w) were investigated using static light scattering, circular dichroism (CD) and viscometry. At 60 °C (coil), the addition of salts caused an increase in the radius of gyration (Rg) and a decrease in peak area within the CD spectrum. As temperatures declined (60–25 °C), gellan appeared to undergo an intramolecular coil–helix transition, which was accompanied by a 15–36% reduction in Rg, depending upon the ionic conditions. Temperature dependence of the molecular ellipticity at 200 nm during heating, described by the van’t Hoff relationship, estimated enthalpic changes for double helix unraveling to range between 7.9 and 11.7 kJ/mole depending on the ionic conditions. At 25 °C (double helix), Rg decreased with the added salts and intrinsic viscosity decreased as a function of increasing Ca2+ (0.1–0.25 mM) or K+ (0.2–0.5 mM) levels.