Microcrystallization of lactose during droplet drying and its effect on the property of the dried particle

Abstract

Spray dried products with controlled crystallinity is desired to realize an improved quality and functionality of the final products. This study used the glass-filament single droplet drying technique to study lactose crystallization behaviour during convective drying. Single lactose droplets with different proportions of α- and β-isomers were subjected to air drying temperatures of 70 °C and 110 °C. Lactose particles dried at 70 °C with higher initial proportions of α-isomer showed the lowest dissolution rate. XRD analysis on the freshly dried particles showed that higher crystallinity was achieved with a higher air drying temperature and a higher initial α-isomer proportion. This observation was confirmed with the SEM observation of lactose particles that were both freshly dried and with a post-drying crystallization process. Dried lactose particles could have a two-layer morphology where the surface shell and the interior part possess different crystallinity, due to the different crystallization kinetics during drying. The results suggest that during drying there is a critical crystallization stage where both droplet temperature and moisture content are sufficiently high, constituting large T − T g driving force. For rapid crystallization to occur. The findings provide experimental support for the solid-phase crystallization theory.