THERMAL, MECHANICAL SAND MOLECULAR RELAXATION PROPERTIES OF STABILIZED SUCROSE SOLUTIONS AT SUBZERO TEMPERATURES

Sub-zero behaviour of sucrose solutions in the presence of xanthan gum , gelatin and guar gum were investigated using differential scanning c alorimetry (DSC), thermomechanical analysis (TMA) and H-1 nuclear magn etic resonance (NMR). Two freezing rate and thermal history dependent phase transitions, denoted T-Tr1 and T-Tr2, were observed. Only proper ly annealed xanthan systems had any influence on the thermal propertie s of freeze-concentrated sucrose solutions (DSC). However, stabilizers altered the rate of thermal deformation (decrease), calculated viscos ity (increase) and compliance (decrease) above T-Tr2, xanthan having t he largest effect. These properties appeared to be enhanced through sl ow 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 propertie s of the unfrozen phase rather than thermodynamic parameters.