Phase transitions of inulin-waxy maize starch systems in limited moisture environments

The moisture sorption isotherms of gelatinized and native waxy maize starch (WMS, constituted by 98% amylopectin) were determined, fitted to the GAB model and compared to the moisture sorption properties of inulin. Crystallinity of native and gelatinized WMS was assessed by X-ray diffraction. The glass transition temperature (T-g) of gelatinized WMS was measured by differential scanning calorimetry (DSC) as a function of moisture content. At 25 degreesC, T-g occurred at a moisture content of approximately 28% (d.b.). The experimental data were fitted to the Gordon-Taylor equation. Concentrated mixed samples of inulin and WMS presented two individual T(g)s, which corresponded to those of the individual components, indicating that no interactions or plasticizing effects existed between them. It was concluded that phase separation had occurred; accordingly, the degree and nature of the phase separation still need to be addressed. (C) 2003 Elsevier Science Ltd. All rights reserved.