Quantitative Evaluation of Microstructural Changes and their Relations with Some Physical Characteristics of Food during Drying

Abstract

Drying is known to affect various quality attributes of a food product, especially its physical properties. However, changes of physical properties or characteristics are generally due to changes of the product microstructure. Nevertheless, not much quantitative information, as opposed to abundant qualitative information, is available to describe in detail relationships between microstructural and physical changes of food undergoing drying. The present study, thus, aimed at studying quantitative relationships between microstructural and selected physical changes of a test material, that is, carrot, undergoing hot air drying at 60 and 80 °C. The microstructural changes were represented quantitatively in terms of the normalized changes of the fractal dimension (ΔFD/FD(0)) of microstructural images of the samples as well as the normalized changes of the sample average cell diameter (ΔD/D(0)), while the physical changes of interest were shrinkage and hardness. The results showed that during an earlier period of drying ΔFD/FD(0) as well as ΔD/D(0) tended to increase with decreasing moisture content; deformation of the microstructures (represented either in terms of ΔFD/FD(0) or ΔD/D(0)) led to increased shrinkage and hardness. On the other hand, deformation of the microstructures existed, while the moisture content did not change much during the final stage of drying. The relationships between ΔFD/FD(0) and both physical changes were quite well established; ΔD/D(0)were also found to correlate well with the physical changes. Either ΔFD/FD(0) or ΔD/D(0)could thus be used as a tool to monitor the apparent physical changes (shrinkage and hardness) of a sample during drying. Either the normalized changes of the fractal dimension of microstructural images of a sample or the normalized changes of the sample average cell diameter can be a useful tool in monitoring the drying process by 1st assessing the product volumetric shrinkage, which can be assessed easily on-line and on a real-time basis by such techniques as image analysis, and then relating the obtained results through microstructural changes to other apparent physical changes, including the product texture.