An exploration of the caking of lactose in whey and skim milk powders

Abstract

The caking of skim milk and non-hygroscopic whey powders was studied and related to the moisture sorption and powder characteristics. Amorphous lactose had an effect on the moisture sorption and caking properties of the spray-dried skim milk (non-instantised) and non-hygroscopic whey powders (containing <5% amorphous lactose). The skim milk powder absorbed more moisture and formed harder cakes more rapidly than the non-hygroscopic whey powder. The thermal profiles of the dairy powders were described by TGA/SDTA (thermal gravimetric analysis integrated with single differential thermal analysis) and used to monitor the water content of the powders (i.e. free water, water of crystallisation, bound water by compounds such as protein and total water). This study suggests that storage at or below 33% relative humidity at 25°C was sufficient to prevent severe caking and the development of a 'sandy' texture in these dairy powders, but not the crystallisation of amorphous lactose and browning of the powder.