Moisture sorption characteristics and glass transition temperature of apple puree powder

P>The aim of this study was to characterise the influence of different foam-mat-drying methods on the moisture sorption characteristics and glass transition temperatures of apple puree powder. Apple puree was foamed with the addition of 2.5% egg albumin and 0.5% methylcellulose. Convective air-drying and microwave-drying techniques were used. Also foamed puree with and without maltodextrin (6% or 15% w/w) was freeze-dried. Moisture equilibrium data of powders were determined by using a static desiccator method in a water activity range of 0.0-0.903. Modulated differential scanning calorimetry (MDSC) was used to obtain the glass transition temperature. No effect of drying method on sorption properties and glass transition temperatures of apple puree powders was observed. The addition of maltodextrin to the apple puree caused an increase in T-g by 10-30 degrees C depending on the amount of incorporated additive. Addition of maltodextrin significantly reduced the hygroscopicity of apple puree powders.