Ricerc@Sapienza

recently proposed moving-boundary model for food isothermal dehydration was applied
to analyze the dehydration kinetics of ellipsoidal cocoa beans, characterized by a moderate shrinkage
and a non-uniform initial distribution of water content between the core and the shell of the bean.
The aim is to predict the influence of air velocity and non-uniformity of the initial water distribution
on the dehydration rates, as well as the temporal evolution of the water content in the core and
in the shell and of the characteristic lengths of the ellipsoidal bean. The model proved capable
of accurately describing the two-phases dehydration process: an initial fast dehydration of the
shell, characterized by higher dehydration rates, followed by a slower dehydration of the core,
characterized by a linear relationship jd = d(T)Xr between the dehydration rate jd and the moisture
ratio Xr. A shortcut method to estimate the effective water diffusivity D is also proposed, deriving
from the basic observation that the asymptotic exponential behaviour of the dehydration curve Xr(t)
for an ellipsoidal bean coincides with that of an equivalent sphere, with the same surface-to-volume
ratio.