Effect of maltodextrin weight fraction on the amorphous state and critical storage conditions of freeze‐dried juices.

Summary: Diagrams relating to water activity (aw), equilibrium moisture content (Xw) and glass transition temperature (Tg) are valuable tools for predicting amorphous fruit powders' storage procedure and stability. Thus, Tg–aw–Xw diagrams were constructed to characterise the amorphous state and define the critical values of water content (Xwc) and water activity (awc) of freeze‐dried juices of strawberry, pineapple, kiwi and prickly pear prepared with maltodextrin at the dry mass fraction (WMD) of 0, 0.4 and 0.8. The Tg and sorption data were fitted with a polynomial equation and the Guggenheim–Anderson–de Boer (GAB) model respectively. A Tukey test was performed to evaluate the difference between critical values of the powders (P < 0.05). The awc and Xwc increase with WMD and depend on the chemical composition of the powders. The highest critical values were found in pineapple powders, ranging from 0.174 to 0.632 and 0.029 to 0.142 dry basis (d.b.), and the lowest ones in kiwi juice powders ranging from 0.029 to 0.550 and 0.013 to 0.129 (d.b.). For WMD of 0.8, however, regardless of juice composition, stable powders in an amorphous state were obtained up to an aw of 0.52 at 25°C. [ABSTRACT FROM AUTHOR]