Sol-Gel Transition of Sodium Gellan Gums with Different Molar Masses in Aqueous Solutions

抄録

Using three kinds of well-purified sodium type gellan gums (Na-gellan, M_w= 12.7x10³, 9.7x10³, 7.1x10³), we studied the effects of molar mass on the sol to gel transition and the coil to double-helix transition in aqueous solutions with and without NaCl, KCl, and CaCl₂ by rheological measurements. In aqueous solutions with and without salts, the temperature dependence of storage modulus (G′) and loss modulus (G") for the three sample solutions of various polymer concentrations (c_p=0.5-5.0%) was measured from 60 to 5 ℃. In aqueous solutions without salts (c_p=0.5-5.0%), the coil to double-helix transition temperature (T_ch) for the three Na-gellans were the same, however, the sol to gel transition temperature (T_sg) depended markedly on molar mass; T_sg of Na-gellan samples decreased with decreasing molar mass. In aqueous solutions with salts (c_p=1.0 %), T_sg and T_ch overlapped, indicating that the sol to gel transition and the coil to double-helix transition for Na-gellans (GF1-GF3) occurred concurrently. It was found that, in salt solutions, T_ch and T_sg were almost independent of molar mass.