Transfers to solid foods - Physical and mathematical models

This article is dedicated to internal transfers of matter and heat in solid foods. These transfers are responsible for the distribution of species concentrations and temperatures in the product, and thus for biochemical and physical transformations within the product. They are presented in the context of solid food processing and preservation, where they play a vital role. Since the basic constituent of food is water, the focus is on the transfer of water in the liquid and vapor phases, and of water-soluble substances.

First, we present the physical mechanisms of species and heat transfer within solid foodstuffs, assimilated to a porous medium. The fundamental transfer laws are then presented, based on the concept of the equivalent continuous medium. In this macroscopic approach, the complexity of pore-scale transport phenomena is reduced to diffusion and permeation terms. We then present the transfer equations obtained by coupling the material and heat (conservation) balance equations with flow expressions. The transfer equations associated with the exchange conditions at the food surface constitute the internal transfer model, the resolution of which provides access to the evolution of concentration, temperature and pressure fields within the food during a process.

The theoretical concepts developed in this article form the basis for mastering unit processes in the food industry, such as freezing, drying and extraction. These applications are presented in the following article .