INFLUENCE OF STABILIZERS AND FREEZING RATE ON THE STRESS-RELAXATION BEHAVIOR OF FREEZE-CONCENTRATED SUCROSE SOLUTIONS AT DIFFERENT TEMPERATURES

Stress relaxation behaviour of frozen sucrose solutions in the presenc e of xanthan gum, gelatin and guar gum was investigated using a thermo mechanical analyzer. Freezing rate and stabilizer type had a significa nt influence on the calculated relaxation time (tau) and asymptotic mo dulus (E(a)) values at temperatures within and above the glassy state. Following slow (2 degrees C min(-1)) and rapid freezing (liquid nitro gen) the temperature corresponding to a large reduction in tau was fou nd to correlate well with previously reported T-g onset of annealed an d non-annealed systems, respectively (-48 degrees C, rapid; -41 degree s C, slow). At -20 degrees C stabilized systems appeared to alter sign ificantly the mechanism of structural relaxation leading to increased tau and short-term viscoelasticity properties determined from E(a) val ues, xanthan and gelatin exerting the greatest effect. It is postulate d that above the critical concentration stabilizer action may evolve f rom modification of the kinetics of the unfrozen phase facilitated by changes in free volume distribution specifically altering the rheologi cal and viscoelastic response of systems at sub-zero temperatures.