The method of slopes was used to estimate the effective moisture
diffusivity of apple slices under different drying conditions.
With decreasing moisture content, the drying characteristics may
change during the drying process. This may be controlled by a
diffusion mechanism which can be described by Ficks' second law.
Although the diffusivity equation is not the best method to fit
experimental data, it provides an approximate way to present a
common quantitative description for drying fruits and vegetables
with respect to moisture transfer, because it provides a description
for an average diffusion coefficient in the entire drying process
(Crank, 1975). In this study, apple slices were assumed to be infinite
plates, according to Ficks' second law, and the effective moisture
diffusivity (Deff) within infinite plates can be estimated from the
following Equation (3).