Diffusion of small molecules in edible films: Effect of water and interactions between diffusant and biopolymer

Mass transfers of various molecules in multiphasic food products lead to quality modification and thus require the use of edible films or coatings in-between the foodstuff. Consequently, it is important to assess the barrier properties and efficiencies of edible films as well as to determine the diffusivities of the migrants. Translational diffusion of a reference molecule such as fluorescein, determined by the fluorescence recovery after photobleaching (FRAP) method, displays a threshold of a critical water content inducing an increase of the molecular mobility, and demonstrates that multiple populations of a single molecular specie can be involved in different diffusion kinetics. Further investigations at a molecular scale through high resolution solid state nuclear magnetic resonance (NMR) enables to go deeper into the understanding of the interactions involved in such a system, in particular on the identification of the possible binding sites of the diffusant on the polymer and on the overall effect of interactions on the polymer organization. Therefore, the appraisal of transport properties in foods by means of reference molecules constitutes a relevant approach to use in combination with molecular investigation of physicochemical interactions with the diffusing substances.