| Abstract
| - The hydrolysis of disodium p-nitrophenyl phosphate catalyzed by alkaline phosphatase was chosenas a model to study the kinetics of changes in frozen food products. The initial reaction rate wasdetermined in concentrated sucrose solutions down to −24 °C, and the enzymatic characteristicsKM and Vmax were calculated. The experimental data were compared to the kinetics predicted byassuming that the reaction was viscosity dependent. Indeed, an analysis of the enzymatic reactiondemonstrated that both the diffusion of the substrate and the flexibility of the enzyme segmentswere controlled by the high viscosity of the media. When the temperature was too low for the viscosityto be measured simply, the Williams−Landel−Ferry equation was used to predict the viscosity,taking, as reference temperature, the glass transition temperature (Tg) corresponding to theconcentration of the freeze-concentrated phase at the test temperature. Predicted values of thereaction rate were very close to the experimental ones in the studied temperature range. Keywords: Sucrose; enzymatic reaction; viscosity; glass transition; diffusion-controlled reaction;prediction
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