Rice grain structural characteristics of sake rice cultivar Hakutsurunishiki for daiginjo-shu brewing

Hakutsurunishiki is a sake rice cultivar bred using Yamadabo (seed parent) and Wataribune 2 (pollen parent), equivalent to a Yamadanishiki sibling. This study evaluated the structural characteristics of the Hakutsurunishiki rice grain that contribute to the brewing characteristics of daiginjo-shu, via a comparison with Yamadanishiki. Hakutsurunishiki brown rice was a little heavy and had a large white core. Observing a cross-section of white rice after soaking revealed that the rice grain structure of Hakutsurunishiki was different from that of Yamadanishiki. Hakutsurunishiki white rice showed fewer voids than Yamadanishiki, promoting a slower water absorption rate. Glucose distribution in rice koji obtained by mass spectrometry imaging showed that Hakutsurunishiki rice koji, like Yamadanishiki, is tsuki-haze type, suggesting that its grain structure is suitable for making rice koji for daiginjo-shu. With these observations, we were able to clarify the structural characteristics of Hakutsurunishiki rice grain.