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. Stable double helices of two linear regions of glucan chains are the basis for the regular packing in a crystalline array. 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.
Molecular structure determines granule structure and properties.
By judicious choice of processing conditions and starch source, one can take advantage of the kinetic constraints to reaching thermodynamic equilibrium, producing desirable metastable states of industrial interest. In our laboratory we study a wide range of molecular architecture in maize starches, using starches obtained from maize endosperm genotypes with single and multiple lesions in the enzymes of the biosynthetic pathway. By comparing the nature of the molecular structure with physical behavior such as the endothermic phase transitions associated with loss of ordered structures, we can gain insight into physical properties of industrial importance, such as turbidity and gelation. Our research initially focused on the branched fractions alone. In combination with other mutations, amylopectins of varied structure result.