GLASS-TRANSITION AND CAKING OF SPRAY-DRIED LACTOSE

Simple test methods to determine the onset temperatures of viscous flo w and caking of spray-dried amorphous lactose are described. The exten t of viscous flow was measured as an increase in the density of lactos e plugs within a cylindrical aluminium compaction apparatus after incu bation for 3 h at a specified temperature. Caking was characterized by an increase in the hardness of the lactose plugs formed. The onset te mperature of viscous flow decreased with increasing water activity, A( w), and corresponded to the onset temperature of glass transition, T-g l. Glass transition temperatures were determined using both differenti al scanning calorimetry (DSC) and nuclear magnetic resonance (NMR) spi n relaxation. The results suggest that elevation of the powder tempera ture above T-gl promotes viscous how and increases the potential for c aking of amorphous food powders.