Solid-state NMR spectroscopy reveals polishing-induced supramolecular disorder in sake rice starch

While the brewing suitability of sake rice is influenced by its structural features, the molecular basis of its starchy core ( shinpaku ) remains unresolved. Here, Yamadanishiki , a widely used sake rice cultivar, polished to 40% was characterized using solid-state nuclear magnetic resonance (NMR) spectroscopy, scanning electron microscopy (SEM), gas-chromatography-mass spectrometry (GC–MS), and amylopectin chain-length analysis. Solid-state 13 C NMR revealed progressive disruption of A-type crystalline order with polishing, particularly in shinpaku , whereas the amylopectin backbone remains unchanged. Complementary solid-state 1 H NMR experiments showed that polishing removes lipid-derived signals, consistent with quantitative GC–MS data. SEM observations showed that shinpaku contains loosely packed starch granules with abundant voids, unlike the dense outer endosperm. These results establish solid-state NMR as a powerful tool for probing starch disorder and demonstrate how polishing enhances water penetration, koji invasion, and brewing suitability. This study presents an integrated solid-state NMR and SEM analysis. • Solid-state 13 C NMR spectroscopy reveals polishing-induced disorder in sake rice starch • Polishing is associated with a loss of lipid-derived 1 H and 13 C NMR signals • Fatty acid profiles obtained by NMR are consistent with GC–MS analysis • SEM observations support NMR findings and show that shinpaku has a porous structure • Solid-state NMR spectroscopy provides a useful approach for probing starch organization in sake riceS