Vibrational spectra analysis of amorphous lactose in structural transformation: Water/temperature plasticization, crystal formation, and molecular mobility

Lactose is a common component found in many foods and dairy products. In this study, the vibrational signatures in the crystalline structure of α -, β -, and α -lactose monohydrate were calculated based on quantum chemistry calculation (QCC), whilst the vibrational spectra in freeze-dried lactose equilibrated at various a w and pre-humidified amorphous lactose (0.33 a w ) stored from 25 to 95 °C were determined by using Raman and FT-IR spectroscopies. The vibrational signatures of crystalline lactose were affected by the presence of water according to QCC results. Water plasticization, involving water insertion, exposure of H-bonding sites, and structure disruption, was accelerated by storage temperature based on Raman and FT-IR spectra analysis. Raman spectra indicated that the crystal formation of lactose was affected by a w and storage temperature. Moreover, the spectral changes assigned in OH group provided useful information for determining the critical a w or temperature when T g -related molecular mobility occurred in lactose-containing products.