Osmotic dehydration (OD) is often applied as a pre-treatment
process. The complex cell wall structure of the food acts
as a semi-permeable membrane, which is not completely selective.
The consequence is counter-current mass transfer flows:
diffusion of water from food to solution and diffusion of solute
from solution to food (Kowalska and Lenart, 2001;
Panagiotou et al., 1998). The mechanisms of water migration
and solid transport are complex in nature and are generally
indirectly deduced during studies. For instance, to describe
mass transfer, Fick’s approximation is traditionally used.
Some simplifications are normally assumed namely the use of
effective diffusion coefficient which takes into account all
transport mechanisms contributing to diffusion (Moreira and
Sereno, 2003). Mavroudis et al. (1998) indicate free convection
as a possible mechanism concerning solute transport during
the first stage in OD of apple tissue, while diffusion dominates
at later stages