Cutting-edge advances on the stability and state diagram of pure β-lactose

A state diagram is a helpful tool to visualize the stability limits of a material subjected to different conditions. The equilibrium state diagram for pure anhydrous beta lactose (Lβ) stability is reported in this work. For this purpose, adsorption isotherms were built at three storage temperatures (15, 25 and 35 °C) in a wide range of water activity (0.07–0.972). The powders obtained were characterized by Raman spectroscopy, X-ray diffraction (XRD), scanning electron microscopy (SEM), and modulated differential scanning calorimetry (MDSC). The results showed high stability of Lβ at the storage temperatures, indicating an adsorption similar to the monolayer content. Conversely, the mutarotation process was triggered by the adsorption of water beyond the monolayer content. Under these conditions, the presence of alpha lactose (Lα) was observed. Furthermore, the glass transition temperature (Tg) of the Lβ was determined in the range of −15 to −1.4 °C at the storage conditions. The present work contributes to the study of the stability of Lβ to establish its technological application as a carrier agent or in the microencapsulation of active ingredients.