Glass Transition Properties as a Function of Water Content for Various Low-Moisture Galactans

The glass transition temperatures (T g) of various low-moisture galactans, such as agars and carrageenans, were measured by differential scanning calorimetry (DSC) and occasionally by dynamic mechanical analysis (DMA). The shift in heat flow on the DSC thermogram was detected for all samples. The typical thermally activated relaxation process was observed in the DMA thermogram for an agar and a carrageenan that were measured as the representatives of galactans, and it was confirmed that the shift on the DSC thermogram was caused by the glass transition. The T g values of agars leveled off at higher water contents. Thus, the minimum T g values of agars were much higher than those of the carrageenans and a sample of wheat starch. The tightness of binding of the water, which was analyzed by proton nuclear magnetic resonance and water sorption isotherm data, was somewhat weaker to an agar than to a carrageenan even for the same water content, suggesting that most of the water molecules sorbed by the agar were free water and could not plasticize it. Keywords: Glass transition; agar; carrageenan; water binding; plasticizability