The influence of the chemical surface composition on the drying process of milk droplets

The functional properties of multi-component particles are strongly affected by their chemical surface composition, for instance in pharmaceutical and food applications. The powders are often produced from emulsions and solutions by convective drying, such as spray drying. A detailed understanding of the drying and shrinkage kinetics of the material is hereby crucial to optimise process design and product characteristics. In this study, a modified analysis technique was implemented into filament single droplet drying to observe the changes in component distribution of two milk model emulsions with drying time as well as the impact thereof on the water evaporation resistance and shrinkage behaviour. The drying droplets were cryogenically flash-frozen at discrete drying times and, subsequent to freeze-drying, investigated in terms of their chemical surface composition and internal fat and protein distribution. The droplets of a high-fat milk model emulsion were covered by a continuous fat film throughout the whole drying process, whereas the droplets of a low-fat model emulsion featured a surface over representation of protein in comparison to the bulk concentration. The protein further enriched near the surface with increasing drying time. In the high-fat system, the lipid surface film reduced the extent of particle shrinkage and impeded the drying process.