Structural analysis of spray-dried powders by confocal laser scanning microscopy

The internal and external morphology of spray-dried powders were investigated as a function of the operating conditions of the spray dryer by using confocal laser scanning microscopy (CLSM) and scanning electron microscopy (SEM). The blend of gum arabic (GA) and maltodextrin (MD) solution, which is normally used in the encapsulated food industry, was prepared at 30% solid content of the mass ratio of GA and MD of 1 to 3. In order to make the powder particles visible by CLSM, fluorescein sodium was used to label the solid materials. The solutions were fed through an Ohkawara L-8 type spray dryer at different inlet air temperatures and atomizing speeds. An increase in the vacuole as well as the particle size was observed when the inlet air temperature was increased. Smaller vacuoles and lower yields of vacuoles were observed when using low atomization speeds. The density of powders decreased with an increase of the inlet air temperature as well as with an increase of the atomizing speed. Furthermore, the surface morphology presented smooth and shriveled particles for all powders, but deeper surface grooving for low inlet air temperatures. More grooves were observed by using a low atomizing speed. (C) 2007 Curtin University of Technology and John Wiley & Sons, Ltd.