The effect of moisture content on the crystallinity and glass transition temperature of inulin

This paper focuses on the physicochemical characterization of inulin, an important fructooligosaccharide with dietary fiber properties, and its dependence on water sorption properties. The moisture sorption isotherm of inulin was determined at 25°C and fitted to the GAB model. Inulinʹs glass transition temperature (Tg) was measured by differential scanning calorimetry (DSC) as a function of water content; the Gordon–Taylor equation was used to fit the experimental data. Relative crystallinity of inulin was determined by X-ray diffraction and DSC studies. Native inulin was found to be a semi-crystalline material, which, at 25°C and storage water activity values below 0.75, was found in a glassy state. When pre-solubilized, inulinʹs relative crystallinity depended on moisture content: crystallinity was low at low moisture contents, while, at water activities above 0.75 (conditions above Tg), it recrystallized and reached native inulinʹs crystallinity level.