Caking and Stickiness of Dairy‐Based Food Powders as Related to Glass Transition

The effects of heating rate, storage temperature and water activity on surface caking (T_sc) and advanced caking (T_ac) of several dairy‐based infant formula powders were determined by the modified ampule and sealed glass test tube methods, respectively. The glass transition temperature, T_g, was determined by differential scanning calorimetry. Observed T_sc and T_ac values were higher at faster scan rates (5 and 10°C/min) compared to a slower heating rate (1°C/3 min). In addition, because of the sample size and the difference in viscous flow time constants, T_ac≥ T_sc≥ T_g. As expected, stability towards collapse and sticking decreased with Increasing amounts of low‐molecular‐weight carbohydrate. The predicted stable storage water activities at room temperature based on T_sc were higher than those observed during storage; however, the water activity at which T_starage= T_g gave a good prediction of the %RH when collapse begins.