Analysis of Water Diffusion and Enzyme Inactivation Mechanisms During Drying of Liquid Foods

Abstract

Drying of liquid foods is a very complicated simultaneous heat and mass transfer process, in which the water diffusion plays a crucial role. The water diffusion coefficient that decreases sharply with decreasing water content must be known in order to predict the drying process. Methods for determining such water diffusivities have been developed on the basis of the regular regime concept. We have developed a very simple method for determining the water diffusivity from the regular regime isothermal drying curves, and applied to various sugar or carbohydrate solutions. The drying behavior of single droplets or slab-shaped samples of sugar solutions were numerically calculated by a drying model with the concentration-dependent water diffusion coefficient determined. Good agreements between experimental and calculated results were obtained. Enzyme inactivation rate constants were measured experimentally over a wide range of sugar concentrations. By using these data the inactivation behavior of enzymes in sugar solutions were simulated. The enzyme was stabilized during drying because the inactivation rate decreases very sharply with decreasing water contents. The numerical calculations simulated the experimental data well.