A knowledge base for the apparent mass diffusion coefficient (DEFF) of foods

A Database of Physical Properties of Foods is to be created in the frame of the European Concerted action project (DOPPOF). Among the various properties, the diffusion properties of foods with respect to moisture, salt and other solute components are to be covered. The aim of the Database is to provide data which were carefully selected, evaluated and entered the under construction database shell. The effective or apparent diffusion property is an important mass transfer property. Values of effective or apparent diffusivities of foods are abundant in the literature and their derivation is the outcome of the application of the Fickian approximation model for mass transfer in foods. The use of chemical potential to be considered as the driving force and the approach "on cell level" is compared to the Fickian approximation approach. The modern alternative has already started to be applied and it is expected to gain increasing importance in the near future. The purpose of this paper is to provide a "knowledge base" for the use of the effective diffusivity data reported in the literature. The Food scientist or Food engineer is warned of pitfalls observed when using such data. Suggestions are also given for the kind of usage or the applicability extent of the data. A description of the main diffusivity measurement methods in both liquid and solid products is, also, given. In addition, measurement methods of activity coefficients are discussed.