Vibrational spectra analysis of amorphous lactose in structural transformation: Water/temperature plasticization,...

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.