Modeling of solute transport inside plant tissue during osmotic dehydration of apple

The accumulation of solutes on the food surface has resulted in notable contradictions between data resulting from modeling and information observed experimentally. Hence, the mechanisms involved in the transport of solutes in the plant tissue during osmotic dehydration (OD) have not been well documented. The purpose of this study was to analyze solute concentration at different depths of osmotically dehydrated apple cylinder with the use of a conventional (sucrose) and a non-conventional (stevia) osmotic agent. Solute concentration was modeled by Fick's law in order to identify the thicknesses within the tissue where the solute is transferred under a diffusive mechanism. Samples were dehydrated in sucrose (30 and 50 degrees Brix) and stevia (3 and 6% w/w) aqueous solutions. Samples were cut in five slices (delta(cut) = 0.5, 2, 4, 7, 10 mm in z direction) from the surface to the food center. Sample properties such as: water loss, solute gain, moisture content, solute concentration and effective diffusivity coefficients at different tissue depths and time periods of dehydration process were determined. Results showed the concentration of solutes was higher in the surface than the center for both osmotic solutions: stevia and sucrose. Fick model did not allow an adequate description of the experimental data in the area of solutes accumulation, suggesting that transfer of solutes on the tissue surface is governed by other transport mechanism different from diffusion. This result opens new ways for future research of the solutes transport within plant tissue. Under this approach, the surperficial impregnation of solutes at the surface and a diffusive phenomenon inside the sample center could be considered.