Tracing fissure information by scanning electron microscopy characterization of naturally fissured surfaces of rice kernels

摘要

Naturally fissured surfaces of rice kernels contain traceable information on fissure formation. Examination of naturally fissured surfaces of rice kernels can help us better understand the rice fissuring mechanism and find an effective way to prevent fissure formation and preserve head rice yield. Rice samples dried at 60degreesC were dehulled by hand. The dehulled kernels were examined individually on a light box to detect fissured kernels. The naturally fissured surface inside a kernel was exposed by gently bending the fissured kernels by hand. The microstructures of the naturally fissured surfaces were then examined under a scanning electron microscope. Results showed that the surface of naturally fissured kernels was composed of two regions. One region, near the center of the kernel, exhibited a cleavage between the boundaries of starch granules. The other region, close to the periphery of the fracture surface, showed a breakage between the cell wall interfaces. The breakage patterns were interpreted by (1) the relative strength of cell wall interfaces vs. starch granule interfaces, and (2) the stress concentration at these two interfaces. The breakage patterns observed in this study seem to support the proposition that fissures are initiated from the outer layers of a rice kernel during the drying process.