Generalized microstructural change and structure-quality indicators of a food product undergoing different drying methods and conditions Original Research Article

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 (ΔFD/FD0) of the sample microstructure and normalized change of the average sample cell diameter (image), 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 ΔFD/FD0 and image 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, ΔFD/FD0 seemed to be a more generalized structure-quality indicator than image.