Stickiness of skim milk powder using the particle gun technique

The particle gun method for investigating the initiation of stickiness of dairy powders was examined using skim milk powder (SMP). The point at which significant stickiness occurred was at a constant temperature above the glass transition temperature (Tg) of amorphous lactose regardless of the temperature and relative humidity (RH) conditions of the air in the particle gun. This point has been called (T–Tg)critical. The initial water activity of SMP did not significantly affect (T–Tg)critical, confirming that stickiness is a surface phenomenon. Changing the particle feed rate did not effect (T–Tg)critical or the rate at which the powder accumulated on the target plate. The errors in measuring the value of (T–Tg)critical and the rate of stickiness development [slope of the deposition line versus (T–Tg)] for SMP were found to be 33.6 ± 0.8 °C and 3.1 ± 0.7% deposition °C−1, respectively, after standardisation of the ambient air conditions around the powder feeder and the initial water activity of the SMP.