Predicting the surface composition of a spray-dried particle by modelling component reorganization in a drying droplet

Abstract

Properties of powders, such as flowability, reconstitution behaviour or particle adhesion, depend on the surface properties, which are related to the surface composition and environmental conditions. Many researchers reported redistribution of the feed components along a droplet radius during spray-drying of multicomponent food systems. This redistribution can be driven by the difference in the diffusivity of the components, component solubility, density, surface activity and hydrophobicity of components. The final composition on the surface of a dried particle is a resultant of all these material properties.This contribution presents an approach to estimate the surface composition of a particle formed during drying a multicomponent droplet. A continuum model of drying of a single droplet in a hot air stream was applied to predict the radial distribution of the components in the particle. The initial droplet consists of three components: water and two solutes, with different diffusion coefficients. In the model, the mass transfer is described by diffusion. The influences of the initial solid content and component ratio on the composition of the most outer layer of the formed particle were studied. An enrichment on the surface in the slowly diffusing component by 10–150% were predicted for different initial total solid contents, solid-based mass fractions of slowly diffusing component in the bulk and drying temperatures. Our model predicts that the initial ratio of the solid components has an impact on the surface composition only at low initial total solids content and that the drying air temperature has a weaker effect on the surface enrichment than the initial total solids content.