Starch molecular structural differences between chalky and translucent parts of chalky rice grains

Chalky rice has an undesirable appearance and reduced commercial value. To understand the relationship between starch structural characteristics and chalkiness, a comprehensive investigation was conducted of molecular structural differences between starch in chalky and translucent parts of the same chalky grains (three Japonica and two Indica rices), this strategy being such as to minimize genetic and environmental effects. Compared to translucent parts, chalky parts had a larger ratio of large to small branched molecules and more short amylopectin chains (degree of polymerization < 35), but fewer longer chains, which affect higher-level starch structures, such as crystallinity. No significant differences in amylose structure were observed. White-belly and white-core chalky grains showed distinguishable starch characteristics, suggesting studying different chalkiness types separately. These findings extend understanding of chalkiness from the perspective of starch structure, and control of this structure can in the future help breeders to develop strategies against the formation of chalkiness.