Mechanical relaxation times as indicators of stickiness in skim milk–maltodextrin solids systems

Abstract

Thermal and water plasticization and glass transition of amorphous components often result in changes in physico-chemical properties of food solids including stickiness and component crystallization. The glass transition temperatures (Tg) of skim milk–maltodextrin solids systems were measured by differential scanning calorimetry (DSC) and a sticky point test was used to determine the sticky-point temperatures (SPT). The mechanical α-relaxation around glass transition was measured by dynamic-mechanical analysis (DMA). The Guggenheim–Anderson–deBoer (GAB) model was fitted to water sorption data and sorption isotherms were established. The glass transition and water sorption properties were dependent on the dextrose equivalent (DE) of the maltodextrin and the skim milk–maltodextrin solids system composition. Maltodextrins and lactose in skim milk solids were miscible and lactose crystallization was delayed in solids containing maltodextrins. The mechanical α-relaxation behavior was governed by the skim milk–maltodextrin solids system composition and was related to the development of stickiness. The α-relaxation at varying frequencies occurred at higher temperatures in solids with increasing maltodextrin contents and the sticky point was governed by the glass transition of the carbohydrates phase.