Experimental investigation and mathematical modeling of water absorption in air-dried chestnuts

Chestnuts are characterized by limited shelf-life because of their high water activity and sugar content. For this reason, air-drying is typically performed to achieve physicochemical and microbiological stability of such fruits. However, undesired structural changes can occur during drying owing to the achievement of high processing temperature. These modifications can affect water permeability ruling out the possibility of uniformly rehydrating the dried fruit. This contribution provides an experimental and modeling study of the rehydration process of air-dried chestnuts. With the objective of characterizing the effect of the drying temperature on water permeability, chestnuts previously dried at 40, 60 and 80 °C are rehydrated by immersion in water at 90 °C and sorption curves are constructed. Under the explored processing conditions, a purely Fickian diffusion model fails to describe the evolution of the absorbed amount of water due to the occurrence of swelling and starch gelatinization. Therefore, a mathematical model is formulated simultaneously accounting for the effect of diffusion, swelling and starch gelatinization on the transport of water. Parametric estimation of the model parameters is performed, based on the results of rehydration tests, by nonlinear regression techniques. In this way, satisfactory agreement between model predictions and derived experimental data is achieved and valuable information about the influence of the drying pre-processing conditions on water transport are obtained. © 2010 Elsevier B.V