Amylose is the linear component of starch, a plant-derived polysaccharide composed of α-D-glucose units, accounting for approximately 20–30% of most starches alongside the branched amylopectin fraction.
Molecular Structure
Amylose consists of long, essentially linear or slightly branched chains of D-glucose monomers linked by α-(1→4) glycosidic bonds. The degree of polymerization typically ranges from 300 to 3000, corresponding to molecular weights of approximately 105–106 Da. In solution, amylose adopts a left-handed single-helical conformation with six glucose residues per turn, forming a hydrophobic core capable of accommodating iodine molecules or lipid ligands. Distinct polymorphic forms include A-type (common in cereal starches), B-type (prevalent in tuber starches and highly hydrated systems), and V-type structures arising from complexation, as revealed by X-ray diffraction analyses.
Biosynthesis and Physicochemical Properties
Amylose is synthesized in plant amyloplasts by granule-bound starch synthase (GBSS), which elongates α-(1→4)-linked glucan chains using ADP-glucose as the activated substrate. Its relative abundance is genetically regulated, with high-amylose crop varieties (e.g., high-amylose maize) containing more than 70% amylose. Physicochemically, amylose displays limited water solubility but forms viscous, pseudoplastic solutions upon heating. It undergoes rapid retrogradation into crystalline B-type structures, leading to firm gel formation, and exhibits reduced enzymatic digestibility due to tightly packed helical arrangements. A characteristic deep blue coloration upon iodine binding reflects charge-transfer complex formation, while thermal behavior is marked by gelatinization onset temperatures typically between 60 and 70 °C.
Biomedical and Nutritional Applications
High-amylose starches are of significant interest in nutrition and biomedicine due to their slow digestibility and ability to form resistant starch (RSII), contributing to a reduced glycemic index and supporting gut health through prebiotic effects. Additionally, the helical structure of amylose enables the encapsulation of bioactive compounds for controlled delivery applications. Amylose-based films and chemically modified derivatives are also employed in biomedical materials, including wound dressings, where their film-forming and biodegradable properties are advantageous.
