We have investigated the hydrolysis of maltodextrins in a high concentration (up to 70%), by means of enzymatic and acid catalysis. The study revealed that the equilibrium compositions of the catalyzed reactions were kinetically determined by the selectivity of the catalyst, the substrate concentration and the reaction time. A model comprising a set of two kinetic equations was used to describe the hydrolysis and condensation reactions of glucoamylase-catalyzed reactions, even to highly concentrated systems. Increased substrate concentration resulted in the formation of more condensation products. The enzyme inhibition was low and was found to be independent of the substrate concentration.