Determination of physical changes of inulin related to sorption isotherms: An X-ray diffraction, modulated differential scanning calorimetry and environmental scanning electron microscopy study

This paper gives a relationship between powdered inulin behaviour and physical parameters determination. Glass transition temperature (Tg) and development of crystallinity were measured in relation to the water moisture of the polymer. These parameters were obtained by Modulated Differential Scanning Calorimetry (MDSC) and powder X-ray diffraction, respectively. In order to change the water content of the powder, adsorption and desorption isotherms (using different relative humidity storage conditions) were done and successfully fitted to the Guggenheim–Anderson–de Boer (GAB) model. Dependent on the relative humidity storage, a caking phenomenon occurred when glass transition temperature was under storage temperature. An Environmental Scanning Electron Microscopy (ESEM) study showed a structural change when water activity increased above 0.56 at 20 °C. A correlation between the increase of the crystallinity and the hardening of the powder was determined. ESEM permitted an observation of the development of some crystal structures among the amorphous system, confirmed by an increase of the diffraction peaks obtained by powder X-ray diffraction. These observations lead to an understanding of the physical characteristics of inulin related to the water moisture.