Analysis of particle-gun-derived dairy powder stickiness curves

The stickiness curves of a range of dairy powders were measured using a particle-gun rig. The stickiness curves for the powders were shown to run parallel but above the curve of the glass transition temperature (T_g) of amorphous lactose. By assuming that the amorphous lactose at the surface of the powder was in equilibrium with the exit conditions of the air from the particle gun, it was found that for any particular dairy powder sample, the amount of powder deposition measured on the particle-gun target disc collapsed into a single function of the temperature difference by which the amorphous lactose T_g at the surface was exceeded. The x-axis intercept of these plots was calculated and designated as (T−T_g)_crit, characterizing the conditions for initiation of stickiness of the powder. The sensitivity of each powder to stickiness problems when placed in conditions where the critical T−T_g value at the surface is exceeded was quantified with the slope of the plot. These results show that it is the amorphous lactose component that is probably the main cause of stickiness in dairy powders and demonstrates how the particle-gun rig can be used to characterize the stickiness behaviour of powders over a wide range of conditions with two parameters.