Non-isotropic shrinkage of potato slabs was studied within the frame of the systematic approach to food engineering systems (SAFES) methodology. Digital images of potato slabs were taken and lateral projected areas (A(lat)) of material during drying were recorded. Two characteristics peaks in graphs A(lat) vs- time were detected. Also, cellular surface area of potato cells was recorded and related to moisture content by means of an empirical equation with in conjunction with SAFES methodology and Alat values at the two afore mentioned peaks, allowed to evaluate intra- and extracellular moisture contents. Fractal dimension (D-f) of solid-air interfaces during drying were also calculated. Graphs of D-f vs. time also showed two peaks which appeared at approximately the same drying times than those for A(lat) which may indicate that inner structures composed of solid-air matrixes are projected towards the surface in the form of fractal solid-air interfaces. (C) 2007 Elsevier Ltd. All rights reserved.