Stickiness, spray-dried powder

If the glass consists in substantial part of low-molar-mass components, like sugars, the material tends to become quite sticky somewhat above Tg. This can occur with several spray-dried powders that take up water from the air the stickiness then causes the powder particles to form a coherent mass, a phenomenon called caking. On the other hand, powder particles can be... 

Adhikari B, Howes T, Leocomte D, Bhandari BR. 2005. A glass transition temperature approach for the prediction of the surface stickiness of a drying droplet during spray drying. Powder Technology 149 168-179. 

Extracts dried on to a water-soluble base are useful in the preparation of powdered drinks. Soft extracts tend to contain about 70% solid matter and can be mixed into a slun y with the substrate and spray-dried or dried in a vacuum oven. The substrate is usually essential to prevent the dried extract from reabsorbing moisture and turning back into a hard or sticky mass. The dried extracts can be dry-blended with other ingredients in a powdered drink formulation. 

The presence of low MW carbohydrates in supports may contribute, via their amorphous state (T < Tg), to possible modification/deterioration of quality and functionality of powders linked with temperature and RH, especially during the spray-drying process and storage crystallization, stickiness, caking (Vega and Roos, 2006). The determination of Tg will be important in predicting the onset of deteriorative reactions. And the choice of supports (proteins adsorption) may help to modify the powder surface (Jayasundera et al., 2009). 

Adhikari, B. Howes, T. Bhandari, B.R. Wood, B.J. The effect of low molecular weight surfactants and proteins on surface stickiness of sucrose during powder formation through spray drying. Journal of Food Engineering, 2009, 94, 135-143. 

For example, powdered milk products remain dry, free-flowing and stable when maintained below the glass transition temperature. However, if the powder picks up moisture from the air or experiences elevated storage temperatures, it may exceed the glass transition curve and become less stable (mbbery state). In this case, powdered milk would be likely to get sticky, and the powder would cake together. In a spray-dryer, operating parameters have to be chosen to ensure a rapid drying... 

Successful drying of sticky, hygroscopic, thermoplastic, or slowly crystallizing products into free flowing agglomerated powders requires powder temperatures at much lower levels than possible in conventional spray dryers. Under those conditions, such materials would tend to adhere to the discharge cone of the tower and potentially produce massive build-up which results in process upsets. Also, completion of drying... 

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