Branched Starch Molecules: Contribution to Ordered Structures in Granular Starch and Dispersed Starch Molecules

A highly branched homopolyglucan of MW up to 200 x 106, the branched fraction of starch, amylopectin, occurs in nature in semi-crystalline form. This observation stands in sharp distinction to the behavior of other branched polymers. The highly ordered nature of the starch granule results from the non-random nature of the branching and the non-random distribution of the linear regions. Stable double helices of two linear regions of glucan chains are the basis for the regular packing in a crystalline array. Single helices from linear glucan regions can also form, around iodine (to form the familiar blue color) or around hydrophobic regions of organic molecules, especially monoacyl lipids. The basis for starch granule and molecular order is the starch synthases and the branching enzymes. The resulting covalent and granule structure determines accessibility to amylolytic enzymes. The granule structure also determines how the granule will behave in industrial use (one important aspect of granule behavior is "gelatinization," which describes the loss of order prior to and during the swelling that occurs with sufficient heat and water, as the granule takes up water). Molecular structure determine