Structure and stability of the glassy state in rapidly and slowly cooled carbohydrate solutions

Solutions of 30% aqueous fructose with and without sodium carboxymethyl cellulose (CMC) were frozen either rapidly in a cryogen or slowly and examined by cryo-scanning electron microscopy (SEM) and by differential scanning calorimetry (DSC) to determine microstructure and glass transition temperatures (T-g). Rapidly frozen samples were then stored for 3 or 14 days at either -75 or -25 degrees C and re-examined by SEM to determine the extent of ice crystal growth that had occurred. All solutions showed evidence of recrystallization after storage at -75 degrees C for 2 weeks. After storage at -25 degrees C for 2 weeks, ice crystal sizes had increased by 20x that seen at -75 degrees C. Samples that were frozen slowly and stored at -25 degrees C produced larger ice crystals than those rapidly frozen; however, as a result of more complete ice crystallization during freezing, they underwent less recrystallization. The presence of stabilizer in the frozen systems reduced recrystallization during storage. Copyright (C) 1996 Published by Elsevier Science Ltd on behalf of the Canadian Institute of Food Science and Technology