REACTION-RATES AT SUBZERO-TEMPERATURES IN FROZEN SUCROSE SOLUTIONS - A DIFFUSION-CONTROLLED REACTION

The hydrolysis of disodium-p-nitrophenyl phosphate catalysed by alkali ne phosphatase was chosen as a model to study the kinetics of changes in frozen food products. The initial reaction rate was determined in c oncentrated sucrose solutions down to -24 degrees C. The experimental data were compared to the kinetics predicted assuming that the reactio n was diffision-controlled and that the diffusion was related to the v iscosity by the Stokes-Einstein relation. When the temperature was too low for the viscosity to be simply measured, the Williams-Landel-Ferr y equation was used to predict the viscosity, taking, as reference tem perature, the glass transition temperature (Tg) corresponding to the c oncentration of the freeze-concentrated phase at the test temperature. Predicted values were very close to the experimental ones, in the stu died temperature range.