The treatment of apple samples with aqueous sucrose
solutions produced a dehydration eect of the solid
tissue. The dehydration rate increased with the osmotic
pressure and temperature of the solution. Simultaneously
an increase in solids content of the sample by
sucrose impregnation was observed. Both transfer processes
were described by means of a simpli®ed model,
previously proposed by Magee et al. (1983), and valid
during the early stages of operation when such changes
were more important and thus relevant for industrial
osmotic treatment processes. Such a model allows
overall mass transfer coecients to be expressed in
terms of process variables, solution concentration and
temperature.
In the case of sodium chloride solutions, the same
model was able to describe dehydration transfer coe-
cients but not the transfer of solute to the material. This
may be due to a more extensive penetration of such
small molecules into the apple tissue with possible
changes induced in its cell membrane, particularly at
high temperatures. This eect coupled with the leaching
of naturally occurring solutes in the apple may lead to a
decrease in the total solids content of the sample. Further
research is required to describe this complex
behaviour.