| Abstract: | Phase and state transitions of granular starches heated in water are studied by dynamic differential scanning calorimetry (DDSC). The DDSC results of various granular starches show a stepwise heat capacity (Cp) change in the storage Cp curve, which starts at the beginning of melting or immediately preceding gelatinization and ends before the melting reaches its peak temperature. Annealing reduces the magnitude of this stepwise change in storage Cp. After the amorphous phase is selectively removed by acid, the stepwise storage Cp is greatly reduced. The stepwise storage Cp increase is not observed when recrystallized linear short chains from enzyme‐debranched waxy maize starch are heated in water. The results show that the stepwise change in Cp observed on the granular starch is a unique property associated with the phase transition of granular structure and reflects a glass transition of the rigid amorphous regions in starch granules. The glass transition of the mobile amorphous phase in granular starch is believed to extend over a broad range of temperatures before gelatinization. A small glass transition below 0°C is directly detected by DDSC and is attributed to part of the mobile amorphous fraction in granular starch. |
