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 Xs′=0.153 (g water/g wet basis) and at this point Tm′=-41.8°C, Tg′=-57.1°C. The state diagram could be used to predict the stability during storage and the necessary storing conditions for Chinese gooseberry products.