Glass transition and enthalpy relaxation of amorphous lactose glass

The glass transition temperature, Tg, 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 Tg. Both Tg 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 Tg (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 Tg. 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.

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