Effects of water and maltodextrin on the glass transition temperature of freeze-dried mango pulp and an empirical model to predict plasticizing effect of water on dried fruits

Effects of water and maltodextrin on the glass transition temperature (Tg) of freeze-dried mango pulp were investigated systematically using differential scanning calorimetry. The Tg of anhydrous mango pulp increased with maltodextrin content, but an abrupt Tg-change was observed between 0.6 and 0.7 maltodextrin weight fraction. The Tg of mango pulp-maltodextrin mixtures decreased with an increase in water content, and water content and water activity at Tg = 25 °C were increased by the addition of maltodextrin. The effect of water content on the Tg was analyzed with the Gordon-Taylor equation, and a fitting parameter (k) was obtained. By investigating the relationship between the anhydrous Tg and k for the mango pulp-maltodextrin mixtures, and many other kinds of dried fruits reported previously, it was found that the relationship could be described by two linear equations. This result will be useful for predicting the Tg-depression of dried fruits induced by water plasticizing.