Abstract
When unpolished glutinous rice is dried, the translucent grains become white and completely opaque. This phenomenon is called ‘ryokuka’ in Japanese, and distinguishes glutinous rice from non-glutinous rice. Opaqueness is a factor in glutinous rice quality. However, over-drying to achieve opaqueness can result in an increase in cracked or broken rice kernels, which lowers quality. Methods for detecting cracked kernels of non-glutinous rice have been established, but these cannot be applied to glutinous rice owing to its opaqueness. We developed a method for detecting cracked kernels in unpolished glutinous rice that relies on diffuse-reflection spectral imaging. The method uses spectral filters and oblique lightning from a halogen light source. We tested illumination methods and wavelengths, using unpolished kernels of ‘Hakucho-mochi’ glutinous rice, grown in Hokkaido. Cracked and normal kernels were observed under visible to near-infrared light. Light in the range of 500 to 1,100 nm enabled clear detection of the cracks in the kernels. Since cracks tend to occur along the short axis of the rice kernel, more cracked kernels could be detected with illumination parallel to the long axis. Using these results, we developed a portable device for detecting cracked kernels in collaboration with Kett Electric Laboratory. The device can detect cracked kernels in unpolished glutinous rice at low cost anywhere.
