The role of coupled water and solute diffusion and product shrinkage during osmotic dehydration

Osmotic dehydration (OD) is a coupled mass transfer operation where foods are partially dewatered while simultaneously impregnated with solute from the solution. Nonetheless, water loss (WL) and solute gain (SG) are treated as independent processes for modeling purposes and the effect of their coupling on the estimation of water/solute diffusivities (D-w, D-s) and equilibrium dehydration/impregnation levels (WLe, SG(e)) has not been elucidated yet. The objective of this study was to develop a new model considering the coupled mass transport of water and solute occurring during OD of foods and to evaluate the contribution of this coupling on the estimation of D-w, D-s, WLe, and SG(e) in comparison with the rigid/shrinking solid assumption. Experimental WL, SG, and volume kinetics were obtained during OD of papaya cubes in sucrose solutions (50 degrees Bx; 45, 55 and 65 degrees C) and further analyzed with the proposed model solved under different assumptions: coupled and partially coupled mass transfer equations (MTEs) in a shrinking solid and uncoupled MTEs in a rigid solid (no shrinkage) with uncorrected and corrected lengths for diffusion. Properties D-w, D-s, WLe, and SG(e) with coupled MTEs and shrinkage were estimated in the ranges of (2.52-5.48) x 10(-10) m(2)/s, (3.91-5.43) x 10(-10) m(2)/s, 0.47-0.53 g/g and 0.18-0.30 g/g, respectively, with partially coupled and uncoupled MTEs leading to a significant overestimation of diffusivities under the tested experimental conditions (up to 281% for water and 75% for solute), even when shrinkage was considered in the 3D model solution. Current findings demonstrate that, like shrinkage, coupling of WL and SG is of upmost importance for a reliable estimation of mass transfer properties during OD.

Automated summary

The objective of this study was to develop a new model considering the coupled mass transport of water and solute occurring during osmotic dehydration (OD) of foods and evaluate its contribution on the estimation of mass transfer properties. Experimental results demonstrated that the coupling of water loss and solute gain is of utmost importance for a reliable estimation of mass transfer properties during OD.