Influence of glass transition on the adhesion of skim milk powder to a stainless steel surface

Many food powders contain amorphous glassy components, such as amorphous sugars, which when given sufficient conditions of temperature and moisture content, will mobilise as a high viscosity flow making the particles sticky. This can lead to powder caking and increased adhesion to surfaces. The transition from the glassy state is established by increasing the powder temperature above its glass transition temperature. Exposing milk powder to about 10-20°C above its glass transition makes the powder more sticky, rendering it a lot more cohesive and also increases its adhesion to a stainless steel surface. This work shows that skim milk powder does adhere more strongly to a stainless steel wall surface when amorphous lactose is above its glass transition temperature and in the sticky zone. However, there is a time dependency effect because the molecular mobility conferring stickiness also initiates crystallisation which in-turn reduces mobility and stickiness to the wall surface over time. Furthermore, powder caking may change the wall friction behaviour of the powder because the powder is different physically.