Studies of the fracture surface of rice grains using environmental scanning electron microscopy

Raw and processed grains of rice (Oryza sativa) were examined using the environmental scanning electron microscope (ESEM), which allows specimens to be imaged at high resolution with minimal preparation. Images were obtained for milled rice grains that were fractured along natural transverse fracture planes. The images showed two distinct features: a smooth surface, where the fracture plane is suggested to be between endosperm cells, and a rough, more disorganised surface, which is likely to correspond to the fracture plane passing through an endosperm cell. Individual starch granules exposed in the fractured surface ranged from 3 to 11 (mu)m in diameter. The ESEM revealed morphological differences between grains of different varieties. Parboiled rice showed a glassy fracture surface in which features of endosperm cells and starch granules were clearly recognisable but smaller than those of uncooked rice grains. Rice grains that had been heated and puffed showed a complete loss of organisational structure. The ESEM was able to capture the effect of processing treatments on the organisational structure of the grains.