# Amylose
**Amylose** is a linear polysaccharide composed of unbranched chains of D-glucopyranose residues joined by α(1→4) glycosidic bonds, and it is one of the two glucose polymers that make up starch, the other being the highly branched amylopectin.[1](https://www.ebi.ac.uk/chebi/CHEBI:28102) Amylose constitutes 5–35% of most natural starches and has a major influence over the properties of starch in foods.[2](https://nph.onlinelibrary.wiley.com/doi/full/10.1111/nph.16858) The French term record of the Office québécois de la langue française defines it as the starch polysaccharide whose macromolecules have a predominantly linear structure, colored dark blue by iodine.[3](https://vitrinelinguistique.oqlf.gouv.qc.ca/fiche-gdt/fiche/8358307/amylose)
| Key fact | Detail |
|---|---|
| Chemical definition | A glucan of unbranched α(1→4)-linked D-glucopyranose residues; the number of glucose subunits is usually 300 to 3000, but can be many thousands[1](https://www.ebi.ac.uk/chebi/CHEBI:28102) |
| Share of starch | 5–35% of most natural starches; amylopectin makes up the remainder[2](https://nph.onlinelibrary.wiley.com/doi/full/10.1111/nph.16858) |
| Branching | Fewer than 1% of linkages are α-1,6 branches, against 4–6% in amylopectin[4](https://www.sciencedirect.com/topics/biochemistry-genetics-and-molecular-biology/amylopectin) |
| Molecular size | Degree of polymerization about 10²–10³ and molecular mass about 10⁴–10⁵ Da in one comparative table; a recent review gives DP of roughly 1000 to 5000 depending on the starch source[4](https://www.sciencedirect.com/topics/biochemistry-genetics-and-molecular-biology/amylopectin) • [5](https://pmc.ncbi.nlm.nih.gov/articles/PMC11437959/) |
| Iodine test | The starch–iodine complex absorbs at about 600 nm, producing a strong dark blue color[6](https://pmc.ncbi.nlm.nih.gov/articles/PMC10856212/) |
| Biosynthesis | Synthesized by granule-bound starch synthase (GBSS), targeted to the starch granule by the protein PTST1[2](https://nph.onlinelibrary.wiley.com/doi/full/10.1111/nph.16858) |
| Nutrition | High-amylose starch behaves as resistant starch, less digestible in the upper gut and acting as a prebiotic in the lower gut[2](https://nph.onlinelibrary.wiley.com/doi/full/10.1111/nph.16858) |
## Structure
Amylose is a long α-1,4-linked chain, typically with a degree of polymerization between 100 and 10,000, carrying rare α-1,6-linked branch points, and it is believed to reside in the amorphous regions of the starch granule.[2](https://nph.onlinelibrary.wiley.com/doi/full/10.1111/nph.16858) Because amylose does not adopt a semicrystalline structure, it is not amenable to [X-ray diffraction](https://www.edgepedia.org/x-ray-diffraction) analysis in the granule, and how it interacts with the amylopectin matrix there remains unclear; some structural biologists place long amylose-like chains in amorphous cavities within the granules, while small-angle [X-ray scattering](https://www.edgepedia.org/x-ray-scattering) experiments suggest the fraction can also infiltrate the amylopectin crystalline structure.[4](https://www.sciencedirect.com/topics/biochemistry-genetics-and-molecular-biology/amylopectin)
In the classical X-ray diffraction model of the iodine–starch complex, Rundle and colleagues concluded that amylose is organized as left-handed helices with an outer diameter of 13 Å and a pitch of 8 Å, each turn corresponding to six 1,4-anhydroglucose units.[7](https://www.fpl.fs.usda.gov/documnts/pdf1996/yu96a.pdf) Amylose does not form stable helices in plain water; molecular dynamics simulations indicate that amylose chains can adopt helix-like shapes in water despite suboptimal hydrogen bonding, but well-defined helical structures form in the presence of iodine, dimethyl sulfoxide, alcohols, or fatty acids.[5](https://pmc.ncbi.nlm.nih.gov/articles/PMC11437959/) The helix's internal diameter and secondary structure vary with environment, including solvent, ionic strength, pH, temperature, and surfactants.[6](https://pmc.ncbi.nlm.nih.gov/articles/PMC10856212/)
## The iodine complex
The deep blue color that iodine produces with starch is the basis of the classic iodine test, and the complex absorbs light at about 600 nm.[6](https://pmc.ncbi.nlm.nih.gov/articles/PMC10856212/) The identity of the iodine species inside the amylose helix has been debated. Many textbooks describe I₂ units aligned inside the helical channel, with the hydrophobic character of I₂ driving the arrangement and non-covalent interactions between the molecules producing charge-transfer bands and the intense blue color.[6](https://pmc.ncbi.nlm.nih.gov/articles/PMC10856212/) NMR and UV-vis studies have shown that iodide ions are not involved in the iodine–amylose helix, although they help dissolve iodine in water, and semiempirical simulations of the UV-vis spectra have been reported to support a stoichiometry of (C₆H₁₀O₅)₁₆.₅···(I₂)₃, refuting Iₙ⁻ species with n = 3, 5, or 7 as candidates.[6](https://pmc.ncbi.nlm.nih.gov/articles/PMC10856212/) Other work proposes a structure of alternating triiodide units and I₂ molecules, and X-ray structures of cyclomaltohexaicosaose (a cyclodextrin model) triiodide inclusion complexes show stacked channels holding triiodide ions at inter-ion distances of 3.66–3.85 Å, providing an atomic-resolution model for the amylose–iodine complex.[6](https://pmc.ncbi.nlm.nih.gov/articles/PMC10856212/) • [8](https://pubmed.ncbi.nlm.nih.gov/12681922/) Large amounts of iodine can also associate outside the helical cavity, with inter- and intra-chain associations contributing.[6](https://pmc.ncbi.nlm.nih.gov/articles/PMC10856212/) At room temperature, molecular iodine binds amylose in the solid state but not in solution, and the solid-state amylose–I₂ complex is not stable in water.[6](https://pmc.ncbi.nlm.nih.gov/articles/PMC10856212/)
## Biosynthesis
Amylose synthesis is chemically simple: the linear chains form through processive elongation by a single enzyme, granule-bound starch synthase (GBSS), which extends α-1,4-linked glucan chains using ADP-glucose as the glucosyl donor.[2](https://nph.onlinelibrary.wiley.com/doi/full/10.1111/nph.16858) A second protein, PROTEIN TARGETING TO STARCH1 (PTST1), targets GBSS to the starch granule.[2](https://nph.onlinelibrary.wiley.com/doi/full/10.1111/nph.16858) Because amylose is synthesized inside the semicrystalline amylopectin matrix of the granule, its synthesis must be tightly coordinated with amylopectin synthesis for granules of correct structure and composition.[2](https://nph.onlinelibrary.wiley.com/doi/full/10.1111/nph.16858) Amylose content is usually low early in seed or tuber development and rises in later stages, consistent with amylose being synthesized within a pre-existing amylopectin matrix.[2](https://nph.onlinelibrary.wiley.com/doi/full/10.1111/nph.16858)
## Occurrence and content across starches
Amylose is present in virtually all land plants examined as well as in green algae, and findings including a cyanobacterial strain carrying a GBSS gene point toward a cyanobacterial origin of the enzyme, with amylose synthesis likely evolving before the divergence of the green and red algal lineages.[2](https://nph.onlinelibrary.wiley.com/doi/full/10.1111/nph.16858) Content varies widely by species and organ. Typical values include maize 22–30%, wheat 25–29%, pea 26–33%, potato 17–21%, cassava 18–20%, indica rice 6–28%, and japonica rice 9–16% by weight; [Arabidopsis](https://www.edgepedia.org/arabidopsis) leaf starch is low at 6–12%, partly because leaf starch turns over within a single photoperiod, leaving little time for amylose synthesis.[2](https://nph.onlinelibrary.wiley.com/doi/full/10.1111/nph.16858) Amylose-free ("waxy" or "glutinous") varieties of maize, barley, rice, and millet have been cultivated for centuries in Asia for their stickier cooking textures, and amylose-free wild accessions of Arabidopsis have recently been reported, suggesting amylose is not as strictly conserved as once thought.[2](https://nph.onlinelibrary.wiley.com/doi/full/10.1111/nph.16858)
## Function and applications
The amylose-to-amylopectin ratio is a pivotal factor affecting the physicochemical properties of starch, including gelatinization, pasting, retrogradation (cooked starch recrystallizing and firming over time), and digestibility.[5](https://pmc.ncbi.nlm.nih.gov/articles/PMC11437959/) Amylose packs tightly, forms films, retrogrades readily, and gives firm gels, so amylose-rich systems need strict moisture control, while amylopectin hydrates rapidly and stays stable under freeze–thaw conditions.[9](https://doi.org/10.1016%2Fj.carpta.2025.101001) Amylose is described as the key component involved in water absorption, swelling, and gelation of starch in food processing.[10](https://cec.nic.in/webpath/curriculum/Module/FDTECH/Paper02/18/downloads/faq.pdf)
**Applications by amylose level.** Amylose-free and low-amylose starches produce stickier textures in cooked foods and clear, stable pastes suited to uses such as papermaking. High-amylose starches act as a type of resistant starch, less digestible in the upper gut and promoting lower gut health as a prebiotic, and they produce firm gels with film-forming properties suited to biodegradable plastic substitutes.[2](https://nph.onlinelibrary.wiley.com/doi/full/10.1111/nph.16858) Common quantification methods rest on three principles: iodine colorimetry, which yields an "apparent amylose" value because it cannot distinguish amylose from long amylopectin chains; lectin precipitation with concanavalin A, which selectively removes amylopectin; and chromatographic separation of debranched chains, where chains longer than about DP 100 are counted as amylose.[2](https://nph.onlinelibrary.wiley.com/doi/full/10.1111/nph.16858)
## References
1. [Amylose (CHEBI:28102), ChEBI, EMBL-EBI](https://www.ebi.ac.uk/chebi/CHEBI:28102)
2. [Seung, D. (2020). Amylose in starch: towards an understanding of biosynthesis, structure and function. New Phytologist 228(5), 1490–1504.](https://nph.onlinelibrary.wiley.com/doi/full/10.1111/nph.16858)
3. [Amylose, Grand dictionnaire terminologique, Office québécois de la langue française](https://vitrinelinguistique.oqlf.gouv.qc.ca/fiche-gdt/fiche/8358307/amylose)
4. [Amylopectin – an overview (comparative structure table of amylose and amylopectin), ScienceDirect Topics](https://www.sciencedirect.com/topics/biochemistry-genetics-and-molecular-biology/amylopectin)
5. [Evaluation of amylose content: Structural and functional properties, analytical techniques, and future prospects, PMC](https://pmc.ncbi.nlm.nih.gov/articles/PMC11437959/)
6. [The Iodine/Iodide/Starch Supramolecular Complex, PMC](https://pmc.ncbi.nlm.nih.gov/articles/PMC10856212/)
7. [The complex of amylose and iodine, USDA Forest Products Laboratory](https://www.fpl.fs.usda.gov/documnts/pdf1996/yu96a.pdf)
8. [X-ray structure of the cyclomaltohexaicosaose triiodide inclusion complex provides a model for amylose-iodine at atomic resolution, PubMed](https://pubmed.ncbi.nlm.nih.gov/12681922/)
9. [Starch–biomacromolecule complexes: A comprehensive review, Carbohydrate Polymer Technologies and Applications](https://doi.org/10.1016%2Fj.carpta.2025.101001)
10. [Consortium for Educational Communication, Food Technology course FAQ](https://cec.nic.in/webpath/curriculum/Module/FDTECH/Paper02/18/downloads/faq.pdf)
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