De- and rehydration behavior of α,α-trehalose dihydrate under humidity-controlled atmospheres

Effects of humidity were investigated on de- and rehydration behavior of alpha,alpha-trehalose dihydrate (T-h) throughout simultaneous measurements of differential scanning calorimetry and X-ray diffractometry (DSC-XRD) and simultaneous thermogravimetry and differential thermal analysis (TG-DTA). When T-h, was heated from room temperature under dry nitrogen atmosphere, a metastable anhydrous crystal (T-alpha) was formed at 105 degreesC after dehydration of T-h. The resulting T-alpha melted at 125 degreesC and became amorphous, followed by cold crystallization from 150 degreesC giving rise to a stable anhydrous crystal T-beta. Under a highly humid atmosphere, on the other hand, T-beta was formed at 90 degreesC directly as a result of T-h dehydration. T-alpha was readily rehydrated and turned back to Th when nitrogen gas with low water vapor pressure of 2.1 kPa was admitted, whereas high water vapor pressure up to 7.4 kPa was required for rehydration of T-beta into T-h. This study provided a picture of pathways that link various solid forms of trehalose, taking into account the effects of a humid environment. (C) 2004 Elsevier Ltd. All rights reserved.