Description of the Convective Air-Drying of a Food Model by Means of the Fractal Theory

Abstract

A slab-shaped model food prepared using glucose solutions and agar as jellifying agent was subjected to drying in an experimental drier. Drying kinetics and surface temperature (ST) distribution along drying were evaluated. When fractal analysis was applied to ST distributions it was possible to observe three stages: the first one, at the beginning of the process, was very short and could not be associated with a fractal dimension. The second one, by far the longest, had a constant value of the fractal dimension of the ST distribution and towards the end of the process, as temperature of the surface of the material tended to homogenise, a final linear stage was found which corresponded to equilibrium conditions. Images of the slab along drying were recorded and showed an increasing heterogeneous appearance as drying proceeds. Grey level intensity plots corresponding to these images also showed an increasing irregularity (higher values of fractal dimension) with drying time. Fractal analysis probed to be a useful tool for describing drying kinetics and for characterising images of samples subjected to dehydration.