Dielectric and Mechanical Properties Around Glass Transition of Milk Powders

Alpha-relaxations were measured from changes in dielectric and mechanical properties around the glass transition of milk powders with varying milk protein contents using dielectric analysis (DEA) and dynamic-mechanical analysis (DMA), respectively. A viscometer method was used to determine the sticky-point temperature (SPT). The -relaxations occurred around the glass transition and were affected by the solids composition and water content. The -relaxation behavior and temperature were mainly governed by the amorphous lactose, but the T was at higher temperatures with increasing protein content. The -relaxations showed increasing molecular mobility, which could explain stickiness of milk powders. The results indicated that dielectric and mechanical relaxations were useful parameters to predict flow characteristics and understand the stickiness development of milk powders during processing and storage as well as to set guidelines for the control of temperature and water content to reduce powder stickiness.