Calorimetric analysis of the structural relaxation in partially hydrated amorphous polysaccharides. I. Glass transition and fragility

The glass transition of low moisture food products is now widely recognised as a key-concept regarding their stability and processability. Differential Scanning Calorimetry is an efficient technique for the measurement of the glass transition temperatures Tgʹs on hydrated products. Thanks to the control of thermal history, this technique can bring more information on the relaxational behaviour of products around the glass transition. Simple thermograms (cooling rate=heating rate=3°C min−1) were recorded, allowing a preliminary characterisation of various hydrated polysaccharides (amylopectin, phytoglycogen, extruded starch, pullulan and dextran): Tg1/2, Tf, ΔCp and other related parameters were determined. After following the cooling rate dependence of the fictive temperatures of different glasses, we calculated their fragility parameter. The significance of the parameters extracted from DSC thermograms was discussed and compared with the fragilities. The influence of the water content on thermal properties was studied on amylopectin. Finally, we attempted to discuss our results in a structure/property perspective developed for polymers.