Drying of liquid food droplets : enzyme inactivation and multicomponent diffusion

In this thesis the drying of liquid food droplets is studied from three different points of view: drying kinetics, enzyme inactivation and multicomponent diffusion. Mathematical models are developed and validated experimentally.

Drying experiments are performed with suspended droplets and with free falling droplets under spray-drying conditions. The experiments with the free falling droplets are performed in a specially designed drying tower using a resonance nozzle. The resonance nozzle is capable of producing equally sized droplets.

Thermal enzyme inactivation kinetics are determined at different water concentrations in separate experiments. The inactivation kinetics can be described by a first order Arrhenius-type model.

A mathematical model based on the binary diffusion equation and the inactivation kinetics is developed that describes the drying kinetics of the droplets as well as the enzyme inactivation. The significance of the spray-air mixing pattern on enzyme inactivation is examined using the developed model.

Slab drying experiments are performed with a ternary food model system. All experiments show that segregation of the dissolved solids can occur. This segregation cannot be described by a binary diffusion equation. Therefore the Maxwell-Stefan multicomponent diffusion equations are applied. Model simulations are used to examine the extent of segregation during spray-drying.