Diffusion mechanisms of solutes in chitosan-based edible films – behaviour in liquid and solid media and comparison between macro and nano scale

摘要

The use of biopolymers for food package and the concept of active and intelligent packaging have received a lot of interest over the last years. The main objective of this work was to investigate the diffusion mechanism of bioactive compounds from chitosan based films into liquid and solid media and to assess behaviour at the nano-scale. For studying the transport to solid medium, Fick's 2nd law with proper boundary conditions was applied to the release of natamycin to cheese. For describing the behaviour of compound release to liquid media, a model accounting for both Fickian diffusion and polymer relaxation (Linear Superimposition Model - LSM) was applied to data on glycomacropeptide (GMP) release to water and on natamycin release to Phosphate Buffer Solution (PBS). Investigation on transport phenomena on a nanolayered film was carried by applying the LSM model to data on methylene blue released from chitosan/k-carrageenan nanolayered films to PBS. From the regression results and analysis of model description of the data, it was possible to infer the transport mechanism in the different tested systems. Diffusion from chitosan films to a solid medium followed Fick's behaviour. As for liquid media, transport from chitosan films was a result of Fick's diffusion and molecule release from the matrix disentangled by swelling, i.e. polymer relaxation. Release of compounds from films produced at the nano-scale ranged from anomalous behaviour to almost Fickian behaviour depending on the position where the compound was incorporated. These results support that special attention must be given to transport properties when design packaging for food products. Moreover, reinforce the idea that phenomena at the nano-scale are different from the ones observed in the macro-scale and that further studies are required for transport phenomena in nanomaterials – phenomena like erosion and disassembly should be considered in the future.