Equilibration of apple tissue in osmotic dehydration: Microstructural changes

The changes in density and porosity and the microstructural development of apple tissue throughout the equilibration in osmotic treatments were analyz ed for different osmotic solution concentrations. The effect of vacuum impr egnation of the sample with the osmotic solution, before the osmotic treatm ent was also studied. Two periods were differentiated in the process. For r elatively short term treatments (24-48 h) cell walls shrunk or separated fr om plasmalemma because of the cell water loss while compositional pseudoequ ilibrium was achieved. Afterwards for long term treatments, a bulk flux of osmotic solution into the fruit tissue occurred in line with the relaxation of mechanical energy accumulated in the deformed cell wall matrix. So, the true equilibrium (chemical plus mechanical), achieved when no changes eith er in sample composition or weight occurred, implied cell wall sphericity a nd sample volume recovery. However, some degree of irreversibility was obse rved in cell wall recovery, especially for osmotic treatments at high conce ntration without previous vacuum impregnation of sample.