Mass transfer modeling in osmotic dehydration: Equilibrium characteristics and process dynamics under variable solution concentration and convective boundary

• Equilibrium and mass transfer during osmotic dehydration (OD) were investigated.
• Theoretical analysis of mass equilibrium is presented.
• Unsteady-state model considers a convective boundary and osmotic media dilution.
• OD experiments in NaCl solutions were conducted with carrot slices as food model.
• Water and NaCl diffusivities as well as mass Biot numbers were calculated.

The aim of this study was to model both the dynamic and equilibrium mass transfer periods for water, osmotic solute and food solids interchange between product and solution during an osmotic dehydration (OD) process. The OD model is able to represent situations where concentration of osmotic media changes during the process or where interfacial resistance to mass transfer cannot be neglected. Water and solute are considered to move within the product by a diffusion mechanism based on Fick's second law, while external convective mass transfer is considered in the fluid. The state-space form of the model is analytically solved for one-dimensional mass transfer in products with flat slab, infinite cylinders and sphere geometries. The developed theory was applied to the analysis of equilibrium and OD dehydration curves of carrot slices obtained at 40 °C in sodium chloride solutions with and without stirring and different ratios between solution volume and product mass. Water and NaCl diffusivities were identified in the narrow ranges of 6.0–7.6 × 10−10 m2/s and 3.5–4.1 × 10−10 m2/s, respectively, demonstrating the applicability of the proposed model under a wide range of operating conditions.