The Structure and Composition of Starch Granules in Green Plants

Starch is a vital storage molecule for energy and carbon in green plants, stored in starch granules which can be found in seeds, roots, and tubers. These granules can take on various shapes, such as spherical, lenticular, or polygonal, depending on the plant species. The structure of starch granules varies depending on the botanical source, with crystallinity ranging from 15% to 45%. Starch granules are known to have a complex, multi-level structure ranging from macro to molecular scales. The molecule itself is a polysaccharide consisting of glucose units, with two major biomacromolecules: amylose and amylopectin.

Amylose is sparsely branched, consisting of α(1-4) bonds and having a molar mass of 105-106 g/mol with a degree of polymerization as high as 600. Amylopectin, on the other hand, is highly branched, consisting of α(1-4) and α(1-6) links with branching points localized every 22-70 glucose units.

It is one of the largest naturally occurring polymers, with a molar mass of 107-109 g/mol. Starch granules also contain small amounts of proteins, lipids, and phosphorus depending on the botanical source, which can interact with the carbohydrate chains during processing and modify the behavior of starch-based materials.

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