Glass transition and the flowability and caking of powders containing amorphous lactose

Many powders contain amorphous components, such as amorphous lactose in milk powders, which when given sufficient conditions of temperature and water content, will mobilise as a high viscosity flow making the particles sticky. This can lead to increased cohesiveness, powder caking and increased adhesion to surfaces. The transition from the glassy state is established by increasing the powder temperature to above its glass transition temperature which can be measured using differential scanning calorimetry. Exposing milk powder to over 10–20 °C above the lactose glass transition makes the powder more sticky, rendering it a lot more cohesive and also increases its adhesion to a stainless steel surface. This glass transition induced stickiness is time-dependent. Over time, crystallisation can take place converting the amorphous lactose into crystalline lactose. Furthermore, the caking behaviour of powders depends on the amount of component present in the amorphous state. Finally, this work presents an approach for applying the measured relationship between the glass transition and water content for predicting caking problems with powders containing amorphous components.