Physical properties of inulin and inulin–orange juice: Physical characterization and technological application

• The physical properties of pure inulin and inulin–orange juice systems were studied.
• Glass transition temperature decreases as water was adsorbed.
• Crystallization was induced by water adsorption and microstructure was observed.
• Overall appearance was related with morphology developed by microstructure.
• Results may be useful in predicting shelf stability of food products.

In this work two systems based on a carbohydrate polymer were studied: inulin as model system and inulin–orange juice as complex system. Both system were stored at different water activity conditions and subsequently characterized. Water adsorption isotherms type II were fitted by the GAB model and the water monolayer content was determined for each system. From thermal analyzes it was found that at low water activities (aw) systems were fully amorphous. As aw increased, crystallinity was developed. This behavior was corroborated by X-ray diffraction. In the inulin–orange juice system, crystallization appears at lower water activity caused by the intensification of the chemical interaction of the low molecular weight species contained in orange juice. Glass transition temperature (Tg), determined by modulated differential scanning calorimeter, decreased with aw. As water is adsorbed, the physical appearance of samples changed which could be observed by optical microscopy and effectively related with the microstructure found by scanning electron microscopy.