Glass transition and state diagram for fresh and freeze-dried Chinese gooseberry

The glass transition temperature and freezing temperature of Chinese gooseberry, which is also called kiwi fruit, prepared at various water activities at 25 C were determined by differential scanning calorimetry (DSC), and used to plot the state diagram for the Chinese gooseberry sample. High moisture content (>0.45, dry basis) samples obtained by adding liquid water into freeze-dried samples, were also analyzed. The state diagram was composed by the freezing curve and the glass transition line, which were fitted according to Clausius-Clapeyron model and Gordon-Taylor model, respectively. The maximal-freeze-concentration point was calculated to be at a moisture content of X-s' = 0.153 (g water/g wet basis) and at this point T-m' = -41.8 degrees C, T-g' = -57.1 degrees C. The state diagram could be used to predict the stability during storage and the necessary storing conditions for Chinese gooseberry products. (C) 2007 Elsevier Ltd. All rights reserved.