Water Activity−Temperature State Diagram of Amorphous Lactose

Development in the glass transition temperature, T g, to reach a stabilized value for amorphous lactose stored at 5, 25, and 38 °C at different water activities varying from a w = 0.21 to 0.59 was followed by differential scanning calorimetry. Combinations of stabilized T g and water activity were used for interpolation of the value of water activity, where T g was equal to the storage temperature. These values of water activity were used to construct a state diagram in the (a w,T)-plane for lactose in the amorphous state from which critical combinations of water activity and storage temperature may be obtained for optimization of storage conditions of lactose-based dry products. Keywords: Lactose; glass transition temperature; T g; water activity; DSC; milk powder