Agitated thin-film drying of foods

AbstractAgitated thin-film drying (ATFD) has been proposed for efficient and mild drying of viscous liquid foods, pastes or pureed foods. We report a study on the influence of product and process parameters on ATFD. During ATFD of spinach leaf slurries, the wall temperature mainly affected the specific evaporation rate, while the absolute evaporation rate was proportional to the feed rate. The fact that blade rotation speed had limited effect on the drying rate suggested that the process is limited by heat transfer through the wall. ATFD is especially suited for slurries that show relatively limited sticky behavior during drying and liquid–solid phase transition with corresponding brittle viscoelastic behavior. This was demonstrated by drying juices from tomato and bell pepper, giving poor results, and by drying solutions from whey protein isolate (WPI) and sucrose, which could be successfully dried.