Morphological and structural properties of amorphous disaccharide lactulose (C12H22O11), obtained by four different amorphization methods (milling, quenching of the melt form, spray-drying, and freeze-drying), are investigated by scanning electron microscopy, polarized neutron scattering, and molecular dynamics simulations. While major differences on the morphology of the different amorphous samples are revealed by scanning electron microscopy images, only subtle structural differences have been found by polarized neutron scattering. Microstructure of the milled sample appears slightly different from the other amorphized materials with the presence of remaining crystalline germs which are not detected by X-ray diffraction. Quantitative phase analysis shows that these remaining crystallites are present in a ratio between 1 and 4%, and their size remains between 20 and 30 nm despite a long milling time of about 8 h. The impact of the change in tautomeric concentrations on the physical properties of lactulose in the amorphous state has been investigated from molecular dynamics simulations. It is suggested that chemical differences between lactulose tautomers could be at the origin of small structural differences detected by polarized neutron scattering.
Keywords: amorphous sugar; crystallites; freeze-drying; milling; molecular dynamics simulation; neutron diffraction; quenching melt; spray-drying; structure.