Moisture sorption characteristics of crystalline and amorphous 2'-fucosyllactose, a human milk oligosaccharide

The moisture sorption characteristics of crystalline and amorphous forms of 2'-fucosyllactose (2'-FL) were investigated and compared with those of two forms of lactose. The moisture sorption isotherms showed that, relative to crystalline α-lactose monohydrate (α-LM), crystalline 2'-FL was more susceptible to moisture sorption. Crystalline 2'-FL exhibited a lower deliquescence point (89.8 %) but threefold greater water solubility (57.1 %) than crystalline α-LM at 25 °C. Time-dependent moisture sorption, X-ray diffraction, and scanning electron microscopy analyses confirmed that amorphous 2'-FL underwent moisture-induced crystallisation (similar to amorphous lactose), but required more humid conditions (a_w > 0.53; a_w > 0.33 for amorphous lactose) due to lower molecular mobility. Dynamic oscillatory rheology showed that amorphous 2'-FL exhibited a higher sticky point temperature (T_s) compared with amorphous lactose at any given a_w, and T_s decreased from 78.9 °C to 43.6 °C as a_w increased from 0.23 to 0.53 due to the plasticizing effect of moisture.