DIFFERENTIAL SCANNING CALORIMETRY OF LOW-MOISTURE APPLE PRODUCTS

Differential scanning calorimetry (DSC) was used to detect thermal pha se transitions in low-moisture apple products, cell walls and related materials. Freeze-dried (FD) apple tissue equilibrated over P2O5 exhib ited a T-g around 11 degrees C, similar to that of FD apple juice and slightly higher than the predicted value for the sugar mixture in juic e (7 degrees C). Samples also showed an endothermic peak around 50-70 degrees C. Cell wall (CW) material from apple prepared by five differe nt methods and dried over P2O5 showed an endothermic peak (onset aroun d 120 degrees C and peak between 130-160 degrees C) caused by water ev aporation. No glass transition was detected in CW preparations for any water activity. The same behavior was observed for microcrystalline c ellulose, 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. (C) 1998 Elsevier Science Ltd. All rights reserved.