Gelation mechanism of agarose

The non-Newtonian behavior and dynamic viscoelasticity of a series of aqueous solutions of agarose were measured with a rheogoniometer. The flow curve, at 25°, of agarose solution approximated to plastic behavior at 0.1, 0.13, and 0.15% concentrations. Gelation occurred at concentration of 0.13% at low temperature (0°). The dynamic modulus of agarose showed a very high value at low temperature, and increased with an increase in temperature, showing a maximum value at 30°, then it decreased. In the presence of NaCl, KCl, CaCl₂, and MgCl₂ for a solution of agarose at 0.08% concentration, the transition temperature, at which dynamic modulus decreased rapidly, was observed at 60°. Gelation was also observed at low temperature (0°) in acid and alkaline range after reaching pH values of 2.3 and 9.5, respectively, by addition of 100m HCl, H₂SO₄, NaOH, and Ca(OH)₂ to a 0.08% agarose solution. A possible mode of intra- and inter-molecular hydrogen bonding within and between the agarose molecules in aqueous solution is proposed.