Relationship between chalkiness and the structural and thermal properties of rice starch after shading during grain-filling stage

Chalkiness is a major concern in rice production and its acceptance and is increased by shade stress. However, the relationship between rice chalkiness and the structural and thermal properties of starch is unclear. Here, we investigated the effect of shade stress on rice starch properties. The chalky grain rate and chalkiness degree significantly decreased with the amylose content, Mn, and Delta H and increased with surface areaand volume weighted mean diameters, branching degree, ratio of 1022/995 cm(-1), and molecular weight polydispersity. Shade stress significantly increased the volumeand surface area-weighted mean diameters and Mw and decreased the amylose content, A chain proportion of amylopectin, Mn, and regularity of starch. These effects led to an increase in the molecular weight polydispersity and branching degree and a decrease in the crystallinity degree and 1045/1022 cm(-1) ratio, thereby reducing starch Delta H and uniformity. These factors contributed to increased chalkiness of rice under shade stress.