Characterization of osmotic dehydrated apple by NMR and DSC

Osmotic dehydration of apple in concentrated sucrose solutions was followed by low-resolution nuclear magnetic resonance. Spin-spin and spin-lattice r elaxation times were measured as a function of degree Brix index of the fru its during the process. A rapid decrease of bath relaxation times was found between 0 and 3 h of soaking. After 3 h of osmotic dehydration, the decay of relaxation times tended to be less dramatic. water mobility changes were analyzed inside the fruits by population of distributed exponentials. The spin-lattice relaxation time distribution showed a reduction of mobility of the water molecules in the cells due to greater sucrose concentration and interaction. The spill-spin relaxation time distribution revealed a shrinka ge phenomenon associated with the removal of Il ater in the cytoplasm, Diff erential scanning calorimetry data showed changes of the freezing point of the dehydrated fruits and the associated enthalpy of crystallization as a f unction of the amount of sugar present in the fruit. Measurements of the te mperature of the maximally freeze-concentrated matrix were in accordance wi th literature darn on similar model sucrose-water solutions. Unfrozen water fractions were also estimated by differential scanning calorimetry from th e melting endotherms. (C) 2000 Academic Press.