TRACING FISSURE INFORMATION BY SCANNING ELECTRON MICROSCOPY CHARACTERIZATION OF NATURALLY FISSURED SURFACES OF RICE KERNELS

Abstract

Naturally fissured surfaces of rice kernels contain traceable information on fissure formation. Examination ofnaturally fissured surfaces of rice kernels can help us better understand the rice fissuring mechanism and find an effectiveway to prevent fissure formation and preserve head rice yield. Rice samples dried at 60.C were dehulled by hand. The dehulledkernels were examined individually on a light box to detect fissured kernels. The naturally fissured surface inside a kernelwas exposed by gently bending the fissured kernels by hand. The microstructures of the naturally fissured surfaces were thenexamined under a scanning electron microscope. Results showed that the surface of naturally fissured kernels was composedof 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. Thebreakage patterns were interpreted by (1) the relative strength of cell wall interfaces vs. starch granule interfaces, and (2) thestress concentration at these two interfaces. The breakage patterns observed in this study seem to support the proposition thatfissures are initiated from the outer layers of a rice kernel during the drying process.