Drying kinetics and viscoelastic properties of concentrated thin films as a model system for spray drying

Abstract

Controlling the development of the particle morphology during spray drying is of large importance to obtain high quality powders. During drying of skin-forming materials it is still unknown how the rheological properties of the skin develop as a function of time, moisture content and temperature. We here studied films prepared from whey protein – maltodextrin mixtures as a model system for spray drying. The rheological properties were assessed by oscillatory shear measurements at relevant high dry matter contents (66–82 w/w%). During drying, the films high in whey protein became brittle and had slower evaporation compared to films high in maltodextrin. Rheological analysis showed that for whey protein rich systems (with higher ratio than 25:75 WP:MD) the films were in structural arrest at the dry matter contents measured. Maltodextrin films on the other hand showed typical viscoelastic polymer behavior, although as little as 1% addition of whey protein altered its viscoelastic properties drastically. The viscoelastic properties could be related to vacuole formation during single droplet drying: samples that undergo structural arrest at a lower dry matter content (high in whey protein), form less and larger vacuoles compared to samples that undergo structural arrest only at high concentration (high in maltodextrin).