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Structure-Functionality Changes in Starch Following Rough Rice Storage



The molecular-level features of starch in relation to the changes in rice functionality during storage are not yet fully elucidated. This work investigated the effects of rough rice storage conditions on starch fine structures and physicochemical properties. Dried rough rice samples (medium-grain Bengal and long-grain Cypress) were stored at 4, 21, and 38°C in temperature-controlled chambers and then periodically removed and evaluated after 1, 3, 5, 7, and 9 months. Flour (powdered head rice) and starch (extracted from head rice by alkali steeping) samples were evaluated for pasting and thermal properties. High-performance size-exclusion chromatography and high-performance anion exchange chromatography were used to characterize starch molecular size and amylopectin chain-length distribution, respectively. Significant changes in starch fine structure were observed primarily on the 38°C lots, and to some extent on the 21°C lots. The decreased amylose: amylopectin ratio, shortened amylopectin average chain length, and the shift in chain-length distribution to shorter branch chains were implicative of molecular-level starch degradation. The flour and starch samples showed inconsistent trends in pasting and thermal properties, thus suggesting the role of not only starch but also its interaction with non-starch components in rice aging.

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