Molecular Association and Dissociation In Formation of Curdlan Gels

Abstract

We examined the formation of curdlan gels by differential scanning calorimetry and electron microscopy. When curdlan heated in water to various temperatures was cooled, an exo-thermic peak appeared at about 40 °C, with formation of hydrogen bonds involving water to give gel. When the cooled preparations were heated again, endo-thermic peaks reappeared at about 60°C and exo-thermic peaks also appeared at higher temperatures. However, no exo-thermic peaks were observed on cooling and then heating above 145 °C. Thus, the gel formation caused by heating to 60-120 °C and cooling is reversible, but that caused by heating to above 145 °C and cooling is irreversible as shown by the heat analysis. In neutralized gel and the gel formed by heating at 55 or 60 °C and cooling, microfibrils of endless length consisting of fibrils of about 100 nm length and 10-25 nm width appeared. In gels obtained by heating at 70, 80, and 100 °C and cooling, microfibrils with released fine stubs appeared. Gels cooled after heating at 120 and 145 °C contained spindle shaped microfibrils of about 100 nm length and 30 nm width. Preparations obtained by heating to 170 °C and cooling gave microfibrils like those formed by unheated preparations.