Thermal, mechanical and molecular relaxation properties of stabilized sucrose solutions at sub-zero temperatures

Abstract

Sub-zero behaviour of sucrose solutions in the presence of xanthan gum, gelatin and guar gum were investigated using differential scanning calorimetry (DSC), thermomechanical analysis (TMA) and 1H nuclear magnetic resonance (NMR). Two freezing rate and thermal history dependent phase transitions, denoted T Tr1, and T Tr2, were observed. Only properly annealed xanthan systems had any influence on the thermal properties of freeze-concentrated sucrose solutions (DSC). However, stabilizers altered the rate of thermal deformation (decrease), calculated viscosity (increase) and compliance (decrease) above T Tr2, xanthan having the largest effect. These properties appeared to be enhanced through slow freezing consistent with changes in free volume. Also, the presence of guar gum appeared to change the NMR t 2 relaxation properties of the system. It is postulated that a mechanism of stabilizer action at sub-zero temperatures involves a modification of the kinetic properties of the unfrozen phase rather than thermodynamic parameters.