An X-ray diffraction analysis of crystallised whey and whey-permeate powders Original Research Article

Amorphous whey, whey-permeate and lactose powders have been crystallised at various air temperatures and humidities, and these crystallised powders have been examined using X-ray diffraction. The most stable lactose crystal under normal storage conditions, α-lactose monohydrate, forms preferentially in whey and whey-permeate powders at 50 °C, provided sufficient moisture is available, whereas anhydrous β-lactose and mixed anhydrous lactose crystals, which are unstable under normal storage conditions, form preferentially at 90 °C. Thus, faster crystallisation at higher temperatures is offset by the formation of lactose-crystal forms that are less stable under normal storage conditions. Very little α-lactose monohydrate crystallises in the pure lactose powders over the range of temperatures and humidities tested, because the crystallisation of α- and β-lactose is considerably more rapid than the mutarotation of β- to α-lactose in the amorphous phase and the hydration of α-lactose during crystallisation. Protein and salts hinder the crystallisation process, which provides more time for mutarotation and crystal hydration in the whey and whey-permeate powders.