Spray drying is often used in food industry to extend the shelf life of the products, reduce the transport weight and to structure food powders in a single processing step. Further on, during drying appealing textures and tastes of the food can be generated. Food powders are often multicomponent systems. During drying of such materials the accumulation of speci c components on the surface might take place depending on the drying conditions.

The surface properties of powders, such as wettability or cohesion, affect the further production steps, like granulation and agglomeration e.g. fluidized bed as well as application by the consumer. The driving forces named in relation to this reorganization of the components are: differences in diffusion coef cients or in hydrophilicity of the components as well as surface activity of the components. Surface properties can be controlled by adjusting the drying rate and thus the time scale of the mass transport processes in the drying particles.

The objective of this project is to understand the development of the surface properties of food powders in order to tailor the properties to the application. The research focuses in particular on the effect of a surfactant on the properties of the lactose powder. The effects of the drying conditions and initial feed composition on the surface properties of lactose powder in presence of surface active whey protein isolate (WPI) as additive are investigated.

Powders are dried at temperatures between 160°C and 200°C and the surface properties of powders such as wettability and stickiness are evaluated in physico-chemical and mechanical tests.

Further on, the project applies a modeling approach of single droplet drying to predict the mass fraction of the additive on the surface of dried particle. The in uence of such parameters as the drying rate, initial feed composition and amphiphilic properties of the additive are investigated.

The results provide an insight into the changes in the surface development during spray drying process. This allows better prediction of the effects of such process parameters as the drying rate and variation in the feed composition on the properties of multicomponent powder.