- Amylose is a linear polysaccharide composed of α-D-glucose units linked primarily through α-1,4-glycosidic bonds. It is one of the two main components of starch, the other being amylopectin, and typically makes up 20–30% of starch content depending on the plant source.
- Unlike amylopectin, which is highly branched, amylose is mostly unbranched, though in some cases it may contain very few α-1,6 branch points. The relatively simple and linear structure of amylose distinguishes it from other storage polysaccharides and contributes to its unique physicochemical properties.
- Structurally, amylose tends to form a helical conformation due to intramolecular hydrogen bonding between glucose residues. Each helix consists of six glucose units per turn, creating a hydrophobic cavity in the center. This cavity can encapsulate small molecules, such as iodine or fatty acids, which explains the classical iodine test for starch: when iodine molecules are trapped inside the amylose helix, they produce a characteristic deep blue color. This helical property not only has analytical significance but also underlies amylose’s role in forming inclusion complexes that influence starch functionality in food and industrial applications.
- Functionally, amylose serves as a plant energy reserve, storing glucose in a compact and less soluble form than amylopectin. Its limited solubility in water arises from strong intermolecular associations and helical packing, which makes it less accessible to enzymatic attack. This contributes to the slower digestibility of amylose compared to amylopectin, giving it significant nutritional importance. High-amylose starches, for instance, are associated with resistant starch formation, which resists digestion in the small intestine and acts as a fermentable fiber in the large intestine. Resistant starch has been linked to improved glycemic control, enhanced satiety, and beneficial effects on gut microbiota, making amylose-rich foods attractive in nutrition and health contexts.
- From an industrial perspective, amylose influences the gelatinization and retrogradation properties of starch. When heated in water, amylose leaches out of starch granules and contributes to gel formation upon cooling. This property is widely exploited in food processing to alter texture, stability, and shelf life of products. However, amylose is also prone to retrogradation, where linear chains reassociate into crystalline structures over time, leading to staling in baked goods and firmness in refrigerated starch-based foods. These characteristics make amylose both a challenge and an asset in food science, depending on the desired product qualities.
- In addition to food applications, amylose has been studied for biomedical and material uses due to its ability to form stable helical complexes. Its inclusion properties have been explored for encapsulating bioactive compounds, controlled drug delivery, and even as a component in biodegradable plastics. Such versatility highlights amylose not only as a dietary carbohydrate but also as a functional biopolymer with wide-ranging applications.
