Rheological and Thermal Studies on the Sol-Gel Transition of Aqueous Solutions of Enzymatically Modified Xyloglucan

Abstract

Aqueous solutions of galactose-removed xyloglucan have unique thermal properties. They have two sol-gel transition temperatures. At the low-temperature transition, a gel is formed on heating and melts on cooling. On the other hand, at the high-temperature transition, the gel melts on heating. These sol-gel transitions are completely thermo-reversible. Thermal properties of xyloglucan with a 43% galactose removal-ratio were studied by differential scanning calorimetry (DSC). DSC curves for the 1% xyloglucan solution showed small peaks. The heating curve showed two small endothermic peaks at 31 °C and 97 °C. The cooling curve showed two small exothermic peaks at 93 °C and 9 °C. These peaks are induced by a structural change in the sol-gel transition. The rheological measurements of xyloglucan with a 43% galactose removal-ratio were performed for the low-temperature transition. The kinetic analysis at a constant temperature showed that the gelling rate increased with increasing concentration of xyloglucan. The 1% xyloglucan solution changes from a sol to weak gel between 15 and 20 °C, and changes from a weak gel to strong gel between 25 and 30 °C. The gelation mechanism of xyloglucan at the low-temperature transition is similar to that of methylcellulose, suggesting that hydrophobic interactions are important.