Hirotsugu Hattori

Viscoelastic properties of xanthan gum hydrogels annealed in the sol state

Viscoelastic properties of xanthan gum aqueous solutions and hydrogels were investigated using a cone-plate type rheometer. The change of viscoelasticity during annealing the solution and cooling to gelation temperature was examined as functions of annealing time, temperature and frequencies. In the annealing process, the storage modulus G′ increases with increasing annealing time. In the subsequent cooling process, G′ of the annealed solution increased, whereas the G′ of non-annealed solution remained almost constant. G′ of hydrogels increased with the increase of annealing temperature and concentration. Based on the experimental results obtained, the structural change of the solution in the annealing process and the structure of gels were investigated.

STRUCTURAL CHANGE IN HYDROGELATION OF HYALURONAN INDUCED BY ANNEALING THE SOLUTION IN SOL STATE

ABSTRACT Structural change of hyaluronan (HA) aqueous solutions in gelation induced by annealing in the sol state was investigated by differential scanning calorimetry (DSC). Melting enthalpy of water (Δ H m ) in the system was used as an index of structural change of HA molecules. Δ H m values remained constant when 3 wt% sol annealed at 60 °C for 1 hr was maintained at the gelation temperature of 5 °C for 40 hours. On the other hand, ΔH m values fluctuated in an oscillatory manner during gelation at 5 °C when the solution was previously annealed at 60 °C for 15 and 18 hr. This fluctuation (variation of Δ H m ) was not observed when the sol was annealed for 48 hours. The results suggests that a conformational change of HA molecules proceeds continuously during gelation when homogenization of the sol state is insufficient.