| The main aim of this work was to analyse the effect of solute on osmotic dehydration, convective air drying and rehydration of apple (var. Granny Smith). To this aim, compositional and structural changes, as well as the kinetics of the processes were analysed.; In the experiments glucose, sucrose and trehalose were used as solutes and different osmotic solutions (water activity 0.96 for dehydration, 0.99 for rehydration) were prepared. Firstly, influence of solute on pulsed vacuum osmotic dehydration of apple tissue, regarding changes of mass, volume and composition, by applying different kinetic models was studied. Rehydration was analysed by following the same procedure, and also, mechanical properties of rehydrated samples and other quality properties were studied. In the second part of the work, our aim was to analyse the establishment and development of water and solute concentration profiles in 9 hours osmodehydrated apple slices throughout storage time. Different models (diffusional and "Advancing Disturbance Front") were applied. Finally, vacuum impregnated samples with the different solutes were air dried, and drying and rehydration kinetics were analysed.; After vacuum impregnation and osmotic dehydration, no significant differences between treatments were found, this resulting from the great variability associated to the coupling of deformation and relaxation phenomena taking place in the vacuum pulse.; The compositional profiles established after osmotic dehydration changed throughout storage time, and differences between solutes were observed: samples treated with trehalose showed a lower value of De as this disaccharide diffused inwards the tissue. Slower changes of the profiles were also observed in this case.; In general, the disaccharides sucrose and trehalose showed similar patterns, (and thus, different to glucose) during convective air drying and further rehydration. Observed differences probably arise from the different molecular weight of the solutes, as well as those on the solutions viscosities, and the possible interactions solute-matrix. In this sense, samples treated with sucrose and trehalose showed smaller coefficients of water effective diffusivity during convective air drying, smaller rehydration ability, better solute holding capacity during rehydration and liquid phase retention after centrifugation. |
