A thermal mechanical compression and cyclone stickiness testing devices were developed for the measurement of surface stickiness properties of food powders. The thermal mechanical compression test (TMCT) determines the changes in mechanical properties during a glass-rubber transition (Tg-r) leading to stickiness behaviour of the powders. The cyclone stickiness test (CST) applies the principle of particle dynamic in the cyclone collector of the spray dryer. Various food powders such as skim milk, fruit juice, whey powders were tested using both techniques and the data were compared with the standard technique.

In TMCT technique, about one g of powder samples is subjected to compression force (around 10-40 N) and scanned under compression at 30°C/min heating rate. The stickiness point is observed at the time of probe displacement when the sample changes from glassy to rubbery state. In CST analysis, about one gram of powder particles are suspended in a vortex of air stream in the cyclone with controlled RH and temperature. The stickiness is observed when the particles agglomerate (cohesion) or stick on the wall (adhesion) of the sample holder. Critical sticky conditions can be established as a boundary between non-sticky and sticky regions. The results obtained from both techniques were compared with Tg analysed by a standard DSC technique.