Structural variation of rice starch in response to temperature during microwave heating before gelatinisation.

Although it is well known that structural variations occur in starch during gelatinisation, little is known about how the structure of starch changes at subgelatinisation levels. The objective of this study was to investigate structural variations of rice starch ascribed to the temperature during microwave heating. Rapid conduction heating was used to imitate the high microwave heating rate through oil bath, which was then compared with traditional conduction heating. Structural changes due to temperature increases were investigated using thermogravimetry and differential scanning calorimetry while the distinct lamellar organisation of starch was obtained through small-angle X-ray scattering. The results showed that the structure of starch responds non-monotonically to temperature rising before gelatinisation, which was also affected by heating rates. The samples treated by microwave and rapid conduction heating essentially underwent the same thermal property changes and the molecular vibration of the microwaves did influence the submicroscopic lamellar structure.