Morphological characterization of the phase behavior of inulin–waxy maize starch systems in high moisture environments

The morphological properties of mixed inulin–waxy maize starch (WMS) systems were characterized as a function of concentration. Macroscopically homogeneous samples were analyzed using light microscopy. Morphological findings were used to explain phase inversion behavior previously determined through rheological analysis. Inulin was labeled with fluorescein isothiocyanate in order to differentiate it from WMS. Fluorescence microscopy was used to characterize phase-separated systems, in which two phases with completely different morphologies co-existed: a WMS-rich phase with inulin crystallites embedded in an amorphous matrix, and an inulin-rich phase with inulin crystallites forming a continuous network. The mechanism of phase separation was determined to be that of nucleation and growth of inulin crystallites. Polarized light microscopy and differential scanning calorimetry were used to verify the crystalline nature of the inulin aggregates in the samples. A ternary phase diagram that summarizes the interactions between inulin and WMS at high moisture contents was generated.