The hydrolysis of maltodextrins (10 DE) by glucoamylase was studied in a batch reactor at temperatures between 40 and 80 degreesC and substrate concentration range from 17 to 300 kg/m(-3). The experimental data were fitted to a model including thermal deactivation of the enzyme. In the model, the reaction rate was correlated with an extended Michaelis-Menten equation including inhibition by product, and the thermal deactivation of glucoamylase was fitted with a first-order reaction. The dependence of rate parameters on temperature was correlated using the Arrhenius equation. The differential equation of the model was integrated and the optimal enzyme demand and temperature were determined for isothermal operation.