Transfer of Water and Active Molecules at the Interfaces in Complex Food Systems: Theoretical and Practical Aspects

During processing, storage and consumption, mass transfer of various molecules (water, gases, flavour compounds or other solutes) occur between the different phases in complex food products, and/or also between the complex food and its surroundings. These mass transfers can lead to physical and/or chemical changes and thus induce food quality modifications. The objective of this presentation is to better understand the behaviour of small molecules at the interfaces, especially in model heterogeneous food systems. Different techniques have been developed to characterize their properties and their impact on the mass transfers. Particularly, techniques such as rotative diffusion cell or Fourier Transform Infra-Red spectroscopic analyses with modelling have been set up. Five examples of results are displayed to demonstrate the influence of the physical-chemical parameters (thermodynamic such as partition coefficient, hydrophobicity… or kinetic parameters like sorption, diffusion and permeation coefficients) on mass transfers. These examples focus on water (liquid or vapour) through polysaccharidic edible films, on flavour compounds in dairy emulsions or in pectic gels. Not only the composition of the matrix but both the structure and the process also influence the mass transfer. Observed results can be explained by similar phenomena, even if applications seem very different.