Moisture Diffusivity in Food and Biological Materials

The spatial distributions of water content and temperature inside moist food or biological materials (native or manufactured) during drying are important in interpretation and prediction of quality changes. The dynamics of drying in modern devices is not simple—for instance, the process of intermittent drying—thus, a liquid diffusion model is expected to be the simplest and hopefully the very effective. In this article, some controversial aspects of the concept of the effective Fickian liquid moisture diffusivity are described and discussed. These discussions are intended to stimulate more interest in working toward a better rationalization of the liquid diffusion concept. It is suggested that such a parameter may even be called a “liquid depletion coefficient” instead to avoid confusion at the fundamental level. An improved alternative model from the effective liquid diffusion model is possible and some new ideas have been explored.