A DIFFERENTIAL SCANNING CALORIMETRY STUDY OF GLASS AND MELTING TRANSITIONS IN STARCH SUSPENSIONS AND GELS

Differential scanning calorimetry (d.s.c.) has been used to study the glass and melting transitions that take place when an aqueous suspension of starch granules, or a partially crystalline starch gel, is heated. A baseline shift was found to accompany both the single major d.s.c. endotherms given by relatively dilute suspensions and gels, and the biphasic endotherms obtained from more concentrated suspensions. The shift, which indicates a change in the heat capacity, starts at the same temperature as the endotherm commences and continues to increase in size until the endotherm is completed. This finding seems to differ in certain respects with other reports suggesting the heat capacity change occurs at the leading edge of the first melting peak for suspensions and does not take place during the melting of starch gels. The change in heat capacity of the suspensions and gels does not appear to be due to a glass transition since this transition was detected at lower temperatures. Hence the present study does not support the suggestion that the melting of the polymers in these starch systems is controlled by a glass transition.