Vitesse de réaction à des températures en dessous de zero dans les solutions de saccharose congelées : le degré de diffusion détermine la vitesse de réaction.

The hydrolysis of disodium-p-nitrophenyl phosphate catalysed by alkaline phosphatase was chosen as a model to study the kinetics of changes in frozen food products. The initial reaction rate was determined in concentrated sucrose solutions down to -24 deg C. The experimental data were compared to the kinetics predicted assuming that the reaction was diffusion-controlled and that the diffusion was related to the viscosity by the Stokes-Einstein relation. When the temperature was too low for the viscosity to be simply measured, the Williams-Landel-Ferry equation was used to predict the viscosity, taking, as reference temperature, the glass transition temperature corresponding to the concentration of the freeze-concentrated phase at the test temperature. Predicted values were very close to the experimental ones, in the studied temperature range.