Physical and chemical changes induced by osmotic dehydration in plant tissues

The osmotic processes induce not only water and solute fluxes in the tissue but also changes in cellular structure, depending on the ratio in which different transport mechanisms act in the system: osmo-diffusional transport of water and solutes and hydrodynamic gains of external solution. The latter is more important in porous tissues, especially when submitted to vacuum impregnation process. In macroscopic samples, different compositional and structural profiles are induced depending on process variables and tissue microstructure; cells near the sample interface are practically perfectly equilibrated in composition with the osmotic solution, whereas the more internal cells may remain unaltered. Compositional-structural profiles developed in the tissue during the process has a great impact on physical (such as optical and mechanical) and chemical properties (such as volatile profile) of the final product, in part due to differences in the number of cells depth, altered and unaltered. The degree in which gas-liquid exchanges occur in the tissue also plays a relevant role. (C) 2004 Elsevier Ltd. All rights reserved.