It is well recognized that changes of many physical characteristics of food during drying are due to changes of the product microstructure. However, since both the physical characteristic and microstructural changes depend on the drying methods and conditions, relationships between the physical and microstructural changes are difficult to be generalized. The aim of this work was to determine if it would be possible to develop a generalized indicator that could be used to monitor microstructural changes of a model food product (carrot cubes) undergoing three different drying methods, i.e., hot air drying, vacuum drying and low-pressure superheated steam drying. Two types of indicators, i.e., normalized change of the fractal dimension (Delta FD/FD(0)) of the sample microstructure and normalized change of the average sample cell diameter ((Delta D) over bar/(D(0)) over bar), were tested. Further investigation was made to determine if the tested indicators could be used to correlate the microstructural changes to apparent physical characteristic changes (shrinkage and hardness). It was found that both Delta FD/FD(0) and (Delta D) over bar/(D(0)) over bar increased with a decrease in the product moisture content, corresponding to an increase in the irregularity of the sample microstructure and a decrease in the sample cell volume; the relationships between the changes of these indicators and product moisture content were similar among all the tested drying methods and conditions. However, Delta FD/FD(0) seemed to be a more generalized structure-quality indicator than (Delta D) over bar/(D(0)) over bar. (C) 2011 Elsevier Ltd. All rights reserved.