Characterization of Grain Quality and Starch Fine Structure of Two Japonica Rice (Oryza Sativa) Cultivars with Good Sensory Properties at Different Temperatures during the Filling Stage

Temperature during the growing season is a critical factor affecting grain quality. High temperatures at grain filling affect kernel development, resulting in reduced yield, increased chalkiness, reduced amylose content, and poor milling quality. Here, we investigated the grain quality and starch structure of two japonica rice cultivars with good sensory properties grown at different temperatures during the filling stage under natural field conditions. Compared to those grown under normal conditions, rice grains grown under hot conditions showed significantly reduced eating and cooking qualities, including a higher percentage of grains with chalkiness, lower protein and amylose contents, and higher pasting properties. Under hot conditions, rice starch contained reduced long-chain amylose (MW 107.1 to 107.4) and significantly fewer short-chain amylopectin (DP 5–12) but more intermediate- (DP 13–34) and long- (DP 45–60) chain amylopectin than under normal conditions, as well as higher crystallinity and gelatinization properties.