Abstract

Differential scanning calorimetry (DSC) was used to detect thermal phase transitions in low-moisture apple products, cell walls and related materials. Freeze-dried (FD) apple tissue equilibrated over P2O5 exhibited a Tg around 11°C, similar to that of FD apple juice and slightly higher than the predicted value for the sugar mixture in juice (7°C). Samples also showed an endothermic peak around 50-70°C. Cell wall (CW) material from apple prepared by five different methods and dried over P2O5 showed an endothermic peak (onset around 120°C and peak between 130-160°C) caused by water evaporation. No glass transition was detected in CW preparations for any water activity. The same behavior was observed for microcrystalline cellulose, apple pectin, pine wood and walnut leaves equilibrated over P2O5. Low-moisture CW exhibited a more hydrophobic behavior than apple tissue as revealed by adsorption isotherms. © 1998 Elsevier Science Ltd. All rights reserved.