Drying and Dried Products Under the Microscope

Food engineers do not often realise that drying of foods and biological materials is a problem of preserving or transforming structures rather than one of removing water. Some unique product properties depend on the structure of dried foods: rehydration and instant properties, flavour retention and sensorial attributes (including colour and texture). The role of structure extends in biochemical and pharmaceutical products to the molecular level and plays key role in viability of desiccated plants and organisms and/or specific activity of dried biomolecules. Nowadays different techniques and probes are available to visualise changes in structure down to the nanostructural level, acquire physicochemical data of micron-size regions and perform physical/mechanical testing in situ. Most novel visualisation methods are non-intrusive permitting image and data acquisition in real time under simulated or current drying conditions. An emerging field of work is that of quantification of structural features using advanced image processing techniques and fractal analysis. Meaningful structure-properties relationships of dried foods can then be derived from their analysis that might contribute to the design of new and specific structures to improve food functionality. Combination of the microstructural approach and concepts from food materials science should result in major advances in this important unit operation and in tailoring product properties.