Glass transition and enthalpy relaxation of amorphous lactose glass

Abstract

The glass transition temperature, T g, and enthalpy relaxation of amorphous lactose glass were investigated by differential scanning calorimetry (DSC) for isothermal aging periods at various temperatures (25, 60, 75, and 90 °C) below T g. Both T g and enthalpy relaxation were found to increase with increasing aging time and temperature. The enthalpy relaxation increased approximately exponentially with aging time at a temperature (90 °C) close to T g (102 °C). There was no significant change observed in the enthalpy relaxation around room temperature (25 °C) over an aging period of 1 month. The Kohlrausch–Williams–Watts (KWW) model was able to fit the experimental enthalpy relaxation data well. The relaxation distribution parameter ( β) was determined to be in the range 0.81–0.89. The enthalpy relaxation time constant ( τ) increased with decreasing aging temperature. The observed enthalpy relaxation data showed that molecular mobility in amorphous lactose glass was higher at temperatures closer to T g. Lactose glass was stable for a long time at 25 °C. These findings should be helpful for improving the processing and storage stability of amorphous lactose and lactose containing food and pharmaceutical products.