Indicative evidence for a conformational transition in ι-carrageenan

Abstract The non-Newtonian behavior and dynamic viscoelasticity of ι-carrageenan solutions were measured with a rheogoniometer. The K salt of ι-carrageenan showed Newtonian behavior 1.5%, whereas the Ca salt of ι-carrageenan showed plastic behavior even at 0.3%. A gelation occurred in polysaccharide concentrations >1.5 and 0.5% for K and Ca salt of ι-carrageenan upon cooling, respectively. The transition temperature, at which dynamic viscoelasticity decreased rapidly, was observed at 45 or 50° at various concentrations of the Ca salt of ι-carrageenan. The dynamic modulus of the Na and K salts forms of ι-carrageenan showed a very high value at low temperature, and increased with an increase in temperature, showing a maximum value at 5°, then it decreased at 0.2% in the presence of CaCl 2 . However, in the presence of KCl, the K salt form of ι-carrageenan showed a very low dynamic modulus upon cooling. The rheological characteristics of the Ca salt of the ι-carrageenan molecule might be essentially attributed to an intramolecular association, contributed by sulfate groups of adjacent 3,6-anhydro- d -galactose and d -galactose residues through Ca 2+ ions with ionic forces.