Relationship Between Multiscale Food Structure and Moisture Transfer Properties
The structure of the food materials has a major impact on the diffusion rate and, consequently, on the value of effective diffusivity or water vapor permeability. On the contrary, water sorption at equilibrium is less or not affected by the structure. Among structure type, porosity particularly affects the diffusion rate. In a porous domain, molecules are allowed to transfer more quickly because of several mechanisms of moisture transfer (e.g., capillary action), vapor diffusion in the pores, and so forth, along with liquid diffusion. In low-porosity materials, liquid diffusion is the main means of moisture transport. The smaller the pores’ size in the matrix of the food domain, the slower the moisture migration. In addition, membranes, crystals, and lipids all contribute as barriers to moisture migration. In such dense materials, elements of structure affecting the diffusion rate are in the nano- or microscale, whereas for porous materials, structural elements at the micro- and macroscales are more predominant.