Hygroscopic Mechanism of Blueberry Powder Based on Glass Transition Theory

Abstract

Blueberry powder was made from two varieties of blueberries, ‘Jewelry’ and ‘Coast’, and the quality changes of blueberry powder before and after moisture sorption were studied. The hygroscopic isotherms of blueberry powder at different temperatures (5, 15, 25, 35 and 45 ℃) were measured by static weighing method, and the state diagram was constructed. The thermodynamic characteristics of net isosteric heat of sorption, differential entropy, and enthalpy-entropy compensation in water sorption were discussed. The results showed that the quality of the two blueberry powders decreased after water sorption, and the powder particles became cohesive and the fluidity decreased. The water sorption isotherms of blueberry powder showed typical J-shaped curves, and the GAB model was the best model to describe the water sorption characteristics of blueberry powder. The state diagram showed that ‘Jewelry’ and ‘Coast’ blueberry powders had good stability when the moisture content based on dry basis was less than or equal to 0.104 5 and 0.107 7 g/g, respectively, and the storage temperature was less than or equal to –30.30 and –32.66 ℃, respectively. The enthalpy-entropy compensation theory showed that the water sorption process of blueberry powder was entropy-driven and non-spontaneous. These results provide a theoretical basis for the selection of processing and storage conditions for blueberry powder.

Keywords

• blueberry powder; glass transition temperature; thermodynamic properties; enthalpy-entropy compensation