Structural, Morphological, and Physicochemical Properties of Starch in Main and Ratoon Rice in South Korea

Rice ratooning is the cultural practice used to produce easily a second rice crop in the same year from the stubble left behind after the main-crop harvest. The major advantage of rice ratooning is that a double crop of rice can be grown for additional returns in areas where it is the main crop. Rice quality properties such as the milling and cooking quality are the most important factors that determine its market acceptability. In this study, the milled rice quality and starch characteristics of the main and ratoon rice crop of three early-ripening rice cultivars in South Korea, ‘Jinbuol’, ‘Joun’, and ‘Junamjoseng’, were estimated. Highly significant variations were detected in the milled rice quality between the main and ratoon rice. The protein and amylose contents of ratoon rice were higher than those of the main rice. The Toyo value (gloss) of the cooked rice of the main crop was lower than that of the ratoon crop, which was due to the higher air temperature during the grain filling period of the main compared with that of the ratoon crop. The mean temperature during the grain filling period of the ratoon rice was favorable (21°C–22°C) for the optimal maturation of early-ripening rice cultivars. The normalized chromatograms of the branch chain length distribution of amylopectin revealed a distinct difference between the main and ratoon rice flour. The starch from the ratoon rice had a higher quantity of short amylopectin chains than those of the starch of the main crop. Scanning electron microscopy examination of the starch showed that the cropping pattern caused differences in the rice starch granule shapes and sizes between the main and ratoon