Determination of Glass Transition Temperature of IMO/D-Mannitol Aqueous Solution and Analysis of Collapse Phenomenon during Freeze-drying Process of Solution

The T_c (collapse temperature) and thermal history of the solution were studied using freeze-drying microscopy and differential scanning calorimetry (DSC), the T_g´ (glass transition temperature of the maximally freeze-concentrated state) was determined according to the two results obtained. The effects of different heating and freezing rated on T_g´ and T_c of isomaltose (IMO) solution were analyzed. The effect of D-Mannitol solution, according to its characteristics reverse glass transition and enhancement of ice crystal structure, on T_g´ and T_c of IMO solution was investigated. It could be concluded that the low and high temperature transitions presented in the thermal history of sample solutions. The measured T_c existed between the end of low temperature transition and the beginning of high temperature transition, and the low temperature transition was identified to be glass transition according to the freeze-concentrated state of solutions. The freezing rates had no significant effect on T_c and T_g´, and T_c was 3~4 ℃ higher than T_g´. However, the higher the freezing rate, the more obvious the collapse phenomenon, with the increasing of heating rate , T_c and T_g´ increased and collapse phenomenon aggravates, T_c increased more obviously, the drying effect was better at 1 ℃/min. With the reduction of IMO/D-Mannitol ratio, T_g´ decreased and the devitrification phenomenon became more obvious, the most was 5:5, the drying effect of 9:1 and 5:5 was better than that of IMO solution, the collapse was worst at 8:2, T_c was 6~7 ℃ higher than T_g´. When a small amount of D-Mannitol was added, the dried structure was better preserved, T_c was higher than that of IMO solution at 9:1, and the drying layer maintained better.