Water Diffusion Coefficient and Modeling of Water Uptake in Packaged Yerba Mate

Effective water diffusion coefficient (Deff) was determined from the kinetics of moisture gain in a yerba mate bed. A value of 1.5 × 10−9 ± 0.4 × 10−9 m2/s was obtained at 40C and 90% relative humidity, by fitting experimental data to the series solution of Fick's second law. A model was developed to predict moisture profile and water uptake in packaged yerba mate. In order to simulate moisture gain in the packaged food, the model considers that the global process of humidity gain is controlled by combined mechanisms of package permeability, product sorption balances and water diffusion within the food bed. The explicit finite difference method was used to numerically solve the resulting equations. The validity of the model was tested by comparing predicted and experimental moisture profiles for high (WVTR ≤ 20 g/m2/day) and low (WVTR ≥ 400 g/m2/day) barrier packages. The model was found to adequately predict the profile of moisture content.