Atomic force microscopy investigation of disorder process on rice starch granule surface

Precise ultra-structures of rice starch granules have been analyzed by atomic force microscopy combined with a structure-disorder process at ambient conditions. Atomic force microscopy is a useful technique to obtain images under atmospheric condition with a nanometer-scale resolution. The images obtained by a high-resolution tapping mode revealed a detailed surface ultra-structure of native rice starch granule with a diameter of approximately 100 nm. The ultra-structures were arranged in series like a chain, and the chain was bundled together into a rod or larger column. After a disorder process using plasticizing/lyophilization of the granules, a significant change in the organization of the surface morphology was detected. Some fine particles of approximately 30 nm in diameter were observed, which might correspond to the individual single cluster in the crystalline region of the starch granule.