Moisture distribution in rice grains used for sake brewing analyzed by magnetic resonance imaging

Water absorption in individual white-core and non-white-core grains of rice varieties used in sake brewing was observed during soaking by magnetic resonance imaging (MRI). Water was absorbed faster in white-core grains than in non-white-core grains and was pooled in the core. Moisture distributions were compared using the line profiles of nuclear magnetic resonance signal intensities (SI profiles) generated from magnetic resonance images of grains soaked for 2 h. SI profiles of white-core and non-white-core grains overlapped despite slight differences in the central and intermediate regions of the grains. A white-core-like structure with loosely packed starch granules was found to exist in the endosperm of non-white-core grains. SI profiles of grains polished to 70% of the yield weight of brown rice were similar in shape to those of grains polished to 90% of the yield, but their overall moisture content was higher after the removal of the hydrophobic grain periphery. A varietal difference in the thickness of the intermediate region, which may affect fissuring resistance in the polishing process, was detected in SI profiles. Differences in water absorbability between parents and their offspring were also apparent from their SI profiles. MRI enabled the detection of variety-specific water-absorption properties in grains.