IMO/D-甘露醇水溶液玻璃化转变温度的确定及冻干过程塌陷现象分析

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

采用冻干显微镜和差示扫描量热法(DSC)研究了溶液的塌陷温度T_(c)和热历史特性,将两种测量结果相结合确定冷冻浓缩状态下的玻璃化转化温度T_(g)´,分析不同升降温速率对低聚异麦芽糖(IMO)溶液T_(g)´及T_(c)的影响,根据D-甘露醇反玻璃化和强化冰晶结构的特性,研究其对IMO溶液T_(g)´和T_(c)的影响。结果表明:溶液的热历史存在低温和高温转变,测定的T_(c)在低温转变结束和高温转变开始之间,根据冷冻浓缩液转变特性,确定低温转变为玻璃化转变;降温速率对T_(c)和T_(g)´无显著影响,且T_(c)均比T_(g)´高3~4℃,但降温速率越大塌陷越严重;T_(c)和T_(g)´随升温速率的增大而增大,T_(c)升高较明显,塌陷随升温速率升高而加剧,1℃/min升温时干燥效果较好;T_(g)´随着IMO:D-甘露醇比值的降低而减小,反玻璃化越明显,5:5时最为明显,9:1和5:5较IMO溶液干燥效果好,8:2时塌陷最严重,T_(c)均比T_(g)´高6~7℃,添加少量D-甘露醇时干燥结构完整,9:1时T_(c)高于IMO溶液的值且干燥层保持较好。

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.