Effect of sectioning and water on resin-embedded sections of corn starch granules to analyze inner structure

Resin-embedded sections and paired block surface of corn starch granules were observed using atomic force microscopy (AFM) and scanning electron microscopy to analyze the fine inner structure of starch granules and observe artifacts. Wrinkles were formed on the starch surfaces because of shear stress caused by the knife. Sectioned starches were isotropically expanded by water, and the growth rings and cracks between the growth rings were observed only on the sections. From this result, it was considered that the growth rings clearly showed shrinkage and/or corrosion of both edges of the ring during drying of the sections. Moreover, many small particles (width, ∼30 nm; height, several nanometers) were clearly observed on the growth rings. These particles could be single clusters (∼10 nm) of amylopectin molecules, considering the effect of the AFM tip radius.