Water activity-temperature state diagram of amorphous lactose.

Development in the glass transition temperature, Tg, to reach a stabilized value for amorphous lactose stored at 5, 25, and 38 degrees C at different water activities varying from aw = 0.21 to 0.59 was followed by differential scanning calorimetry. Combinations of stabilized Tg and water activity were used for interpolation of the value of water activity, where Tg was equal to the storage temperature. These values of water activity were used to construct a state diagram in the (aw,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.