Amylose, the linear constituent of starch, consists of α(1,4)-linked glucose monomers. Although weakly involved in the crystalline structure of starch, it can be recrystallized in a variety of allomorphic types, including those encountered in native starch (A- and B-types). Amylose can either be extracted from starch or produced in vitro by enzymatic synthesis using amylosucrase or phosphorylase. Recrystallization and self-association of amylose in aqueous solutions have been widely studied to understand both the crystallization of starch during biosynthesis and the structural changes that occur during starch processing. Depending on the chain length, concentration, and temperature, gels, spherulites, or lamellar crystals can be formed with A or B allomorphic type. Other ligand-dependent allomorphs (the various V-types) are obtained when amylose is complexed with molecules such as alcohols, lipids, or flavours. Amylose also self-associates into networks, spherulites, or axialites during in-vitro enzymatic synthesis by amylosucrase. When a highly branched acceptor like glycogen is used, dendritic nanoparticles are formed by elongation of the external chains. The recrystallization of amylose extracted from starch and the self-association of amylose during its in-vitro synthesis are described. The amylose properties are discussed in terms of polymer behaviour and model systems to investigate the structure and formation of starch granules.

Model A-type amylose single crystals were prepared by recrystallizing dextrins from acid-hydrolyzed native starch and narrow fractions of short chains of enzymatically synthesized amylose, in dilute water/acetone solutions. In most cases, spindle-shaped crystals with a sharp, round or flat apical end were formed, organized in rosettes or fan-like assemblies. The morphology and crystal size were shown to strongly depend on the average degree of polymerization (DP), distribution width (DW), and degree of branching of the chains. The largest and most clearly faceted single crystals were prepared using fractions of synthetic amylose. Typically, 5-10 μm long crystals were obtained from fractions with 17 ≤ DP ≤ 20 and DW ≤ 8. Chains with DP > 40 and a high polydispersity formed ill-defined networks of smaller crystallites. Fractions of branched and more polydisperse limit dextrins yielded crystals smaller than those obtained from narrow fractions of synthetic amylose. The morphological analysis of faceted single crystals combined with electron diffraction data confirmed that the double helices were oriented along the long dimension of the crystal and packed into lamellae with a parallelogram cross section defined by the a and b directions of the monoclinic unit cell of A-amylose. The lamellae are stacked along the c-axis that is oriented parallel but opposite to the growth direction of the crystal.