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Morphology and Molecular Organization of Developing Wheat Starch Granules

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Title: Morphology and Molecular Organization of Developing Wheat Starch Granules
Author: Waduge, Renuka N.
Department: Department of Food Science
Program: Food Science
Advisor: Seetharaman, Koushik
Abstract: During starch synthesis, knowledge of how the supra molecular organization of starch granules occur is still unknown. This dissertation begins exploring the changes to wheat starch morphology, structure and organization during granule development. Starches from wheat seeds harvested at different days after anthesis were isolated and studied for their molecular organization at different scales. The interaction of granular starch to iodine vapor was used to reveal information about the physical state of the polymers in the granules. Both large and small granule populations initiated as spherical shaped granules, but large granules changed into lenticular shape, while small granules remained spherical. Blocklet, lamellae, and crystalline structures were well developed already at seven days of maturity, suggesting their presence at the center of mature granules. Furthermore, (i) the size of blocklets decreased from center to the periphery in both granule populations, but at all developmental stages, they were larger in small granules than in large granules; (ii) Lamellae repeat distance was shorter close to the center of granules; (iii) B-type crystallites were mixed with A-type crystallites at the center of granules from both populations, but the proportion of B-type crystallites was higher in large granules, which correlated with a higher proportion of amylopectin long chains in these granules; (iv) The relative crystallinity (RC) of starches from both populations was higher at the center of the granule than that at the periphery. RC was lower in large granules than in small granules suggesting influence of the higher amylose content in large granules, which introduces more defects reducing RC. AFM visualized surfaces with features different from the regular type of surface among immature starch granules, which was interpreted as the amorphous growth ring of the starch granule. Exposure of starches to iodine vapor demonstrated different levels of molecular organization between them and revealed possible interaction of inter-cluster chain segments and spacer segments of amylopectin with iodine. In-situ AFM imaging of the granule surface exposed to iodine vapor under humid conditions revealed that glucan polymers or polymer segments in between and on top of blocklets have the ability to interact with iodine.
Date: 2012-05

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