Moisture and Salt Transfers During Constant Temperature Drying of Gelatin Gels: Effects of Composition and of Water Flux Intensity

Abstract

A drying cell was set up to generate salt and moisture gradients in added and free salt gelatin gels maintained at constant temperature. Fluxes from 30 × 10−6 to 280 × 10−6 kg water m−2s−1 were generated in the gels. The water and chloride profiles were measured by slicing and analysis of moisture and chloride. The experimental moisture and salt profiles were used to estimate the apparent diffusivities of water and chloride as a function of composition and process variables. At high and medium promoted water fluxes, salt transfers were accelerated. At low fluxes the rates of mass transfer were small and profiles were flatter. The experimental profiles showed a cross diffusion of moisture and salt occurring in the liquid phase for the investigated ranges of water flux. Water and chloride diffusivities varied respectively from 8 × 10−10 to 1 × 10−11m2s−1 and from 8 × 10−11 to 8 × 10−10m2s−1 for moisture and salt contents varying respectively from 0.6 to 9.5 kg water kg−1 anhydrous gel and from 2 to 8 g chloride 100 g−1 water. Moisture diffusivity depends on the initial structure and composition of the gel. It decreases with decreasing of moisture content. Chloride diffusivity remains relatively constant with chloride content. Moisture and chloride diffusivities measured at high and medium evaporated moisture fluxes in gelatin gels are higher than those measured at low moisture fluxes.