Amylose: Difference between revisions

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| IUPACName = (1→4)-α-<small>D</small>-Glucopyranan

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| ChEBI_Ref = {{ebicite|changed|EBI}}

| ChEBI = 28102

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| Formula = Variable

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| Appearance = White powder

| Solubility = Insoluble<ref>{{cite journal |first1=Mark M. |last1=Green |first2=Glenn |last2=Blankenhorn |first3=Harold |last3=Hart |doi=10.1021/ed052p729 |title=Which Starch Fraction is Water-Soluble, Amylose or Amylopectin? |journal=Journal of Chemical Education |date=November 1975 |volume=52 |page=729 |issue=11 |bibcode=1975JChEd..52..729G | quote = ... amylose is the water-insoluble starch component.}}</ref>

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'''Amylose''' is a [[polysaccharide]] made of α-<small>D</small>-[[glucose]] units, bonded to each other through α(1→4) [[glycosidic bonds]]. It is one of the two components of [[starch]], making up approximately 20–30%. Because of its tightly packed [[Helix|helical]] structure, amylose is more resistant to digestion than other starch molecules and is therefore an important form of [[resistant starch]].<ref>{{cite web |url=http://www.healthyeatingclub.org/info/articles/nutrients/resisstarch.htm |title=Resistant starch |access-date=2010-07-02 |url-status=dead |archive-url=https://web.archive.org/web/20100924043047/http://healthyeatingclub.org/info/articles/nutrients/resisstarch.htm |archive-date=2010-09-24 }}</ref>

[[File:AmyloseA.gif|thumb|Amylose A is a parallel double-helix of linear chains of glucose]]

Amylose is made up of α(1→4) bound glucose molecules. The carbon atoms on glucose are numbered, starting at the aldehyde (C=O) carbon, so, in amylose, the 1-carbon on one glucose molecule is linked to the 4-carbon on the next glucose molecule (α(1→4) bonds).<ref>Nelson, David and Michael M. Cox. Principles of Biochemistry. 5th ed. New York: W. H. Freeman and Company , 2008.{{page needed|date=March 2019}}</ref> The [[structural formula]] of amylose is pictured at right. The number of repeated glucose subunits (n) is usually in the range of 300 to 3000, but can be many thousands.

There are three main forms of amylose chains can take. It can exist in a disordered amorphous conformation or two different helical forms. It can bind with itself in a [[double helix]] (A or B form), or it can bind with another hydrophobic guest molecule such as [[iodine]], a [[fatty acid]], or an [[aromatic compound]]. This is known as the V form and is how [[amylopectin]] binds to amylose in the structure of [[starch]]. Within this group, there are many different variations. Each is notated with V and then a subscript indicating the number of glucose units per turn. The most common is the V₆ form, which has six glucose units a turn.<ref>[https://log-web.de/chemie/Start.htm?name=amylose_V&lang=en a visualisation with references to the literature is found here ]</ref> V₈ and possibly V₇ forms exist as well. These provide an even larger space for the guest molecule to bind.<ref>{{Cite journal

| last1 = Cohen | first1 = R.

| last2 = Orlova | first2 = Y.

| last3 = Kovalev | first3 = M.

| last4 = Ungar | first4 = Y.

| last5 = Shimoni | first5 = E.

| title = Structural and Functional Properties of Amylose Complexes with Genistein

| doi = 10.1021/jf800255c

| journal = Journal of Agricultural and Food Chemistry

| volume = 56

| issue = 11

| pages = 4212–4218

| year = 2008

| pmid = 18489110

}}</ref>

This linear structure can have some rotation around the [[Dihedral angle|phi and psi angles]], but for the most part bound glucose ring oxygens lie on one side of the structure. The α(1→4) structure promotes the formation of a [[helix]] structure, making it possible for hydrogen bonds to form between the oxygen atoms bound at the 2-carbon of one glucose molecule and the 3-carbon of the next glucose molecule.<ref name="www1.lsbu.ac.uk">{{cite web|url=http://www1.lsbu.ac.uk/water/hysta.html |title=Starch |access-date=2010-05-25 |url-status=dead |archive-url=https://web.archive.org/web/20120114225823/http://www.lsbu.ac.uk/water/hysta.html |archive-date=2012-01-14 }}</ref>

Fiber X-ray diffraction analysis coupled with computer-based structure refinement has found A-, B-, and C- polymorphs of amylose. Each form corresponds to either the A-, the B-, or the C- starch forms. A- and B- structures have different helical crystal structures and water contents, whereas the C- structure is a mixture of A- and B- unit cells, resulting in an intermediate packing density between the two forms.<ref>{{Cite journal | doi = 10.1002/star.19780300302| title = The Crystal Structures of A-, B- and C-Polymorphs of Amylose and Starch| journal = Starch - Stärke| volume = 30| issue = 3| pages = 73–78| year = 1978| last1 = Sarko| first1 = A| last2 = Wu| first2 = H.-C. H}}</ref>

==Physical properties==

Because the long linear chains of amylose more readily crystallize than [[amylopectin]] (which has short, highly branched chains), high-amylose starch is more resistant to digestion.<ref name="pmid24228189">{{cite journal |vauthors=Birt DF, Boylston T, Hendrich S, Jane JL, Hollis J, Li L, McClelland J, Moore S, Phillips GJ, Rowling M, Schalinske K, Scott MP, Whitley EM | title=Resistant starch: promise for improving human health | journal= [[Advances in Nutrition]] | volume=4 | issue=6 | year=2013 | pages=587–601 | pmc=3823506 | doi=10.3945/an.113.004325 | pmid=24228189 }}</ref> Unlike amylopectin, amylose is soluble in water.<ref>{{cite web | url = http://www.eric.ed.gov/ERICWebPortal/custom/portlets/recordDetails/detailmini.jsp?_nfpb=true&_&ERICExtSearch_SearchValue_0=EJ128481&ERICExtSearch_SearchType_0=no&accno=EJ128481 | title = Which Starch Fraction is Water-Soluble, Amylose or Amylopectin? | quote = A survey of 22 popular organic chemistry textbooks showed that only four correctly stated that of the two components of starch, amylopectin is the water-soluble, and amylose is the water-soluble.}}</ref><ref>{{Cite journal | doi = 10.1021/ed052p729| title = Which starch fraction is water-soluble, amylose or amylopectin?| journal = Journal of Chemical Education| volume = 52| issue = 11| pages = 729| year = 1975| last1 = Green| first1 = Mark M| last2 = Blankenhorn| first2 = Glenn| last3 = Hart| first3 = Harold| bibcode = 1975JChEd..52..729G}}</ref> It also reduces the crystallinity of amylopectin and how easily water can infiltrate the starch.<ref name="www1.lsbu.ac.uk"/> The higher the amylose content, the less expansion potential and the lower the gel strength for the same starch concentration. This can be countered partially by increasing the granule size.<ref>{{Cite journal | doi = 10.1016/S0260-8774(00)00236-3| title = Relationships between thermal, rheological characteristics and swelling power for various starches| journal = Journal of Food Engineering| volume = 50| issue = 3| pages = 141–148| year = 2001| last1 = Li| first1 = Jeng-Yune| last2 = Yeh| first2 = An-I| url = http://ntur.lib.ntu.edu.tw/bitstream/246246/189885/1/40.pdf}}</ref><ref>{{cite journal | pmc = 4519444| year = 2014| last1 = Pycia| first1 = K| title = Physicochemical, thermal and rheological properties of starches isolated from malting barley varieties| journal = Journal of Food Science and Technology| volume = 52| issue = 8| pages = 4797–4807| last2 = Gałkowska| first2 = D| last3 = Juszczak| first3 = L| last4 = Fortuna| first4 = T| last5 = Witczak| first5 = T| pmid = 26243900| doi = 10.1007/s13197-014-1531-3}}</ref>

Amylose is important in plant energy storage. It is less readily digested than [[amylopectin]]; however, because of its helical structure, it takes up less space than amylopectin. As a result, it is the preferred starch for storage in plants. It makes up about 30% of the stored starch in plants, though the percentage varies by species and variety.<ref name="Wang1">{{Cite journal | doi = 10.3389/fpls.2017.00469| pmid = 28421099| pmc = 5379859| title = Progress in High-Amylose Cereal Crops through Inactivation of Starch Branching Enzymes| journal = Frontiers in Plant Science| volume = 8| pages = 469| year = 2017| last1 = Wang| first1 = Juan| last2 = Hu| first2 = Pan| last3 = Chen| first3 = Zichun| last4 = Liu| first4 = Qiaoquan| last5 = Wei| first5 = Cunxu| doi-access = free}}</ref>

The digestive enzyme [[Alpha-amylase|α-amylase]] breaks down starch molecules into [[maltotriose]] and [[maltose]], which can be used as sources of energy.

Amylose is also an important thickener, water binder, emulsion stabilizer, and gelling agent in industrial and food-based contexts. Loose helical amylose chains have a [[hydrophobic]] interior that can bind to hydrophobic molecules such as [[lipids]] and [[aromatic compounds]]. The one problem with this is that, when it crystallizes or associates, it can lose some stability, often releasing water in the process ([[syneresis (chemistry)|syneresis]]). When amylose concentration is increased, gel stickiness decreases but firmness increases. When other things, including [[amylopectin]], bind to amylose, the [[viscosity]] can be affected, but incorporating κ-[[carrageenan]], [[alginate]], [[xanthan gum]], or low-molecular-weight sugars can reduce the loss in stability. The ability to bind water can add substance to food, possibly serving as a fat replacement.<ref>{{Cite journal | doi = 10.1016/j.carbpol.2009.03.004| title = Impact of molecular structure of amylopectin and amylose on amylose chain association during cooling| journal = Carbohydrate Polymers| volume = 77| issue = 4| pages = 807–815| year = 2009| last1 = Chung| first1 = Hyun-Jung| last2 = Liu| first2 = Qiang}}</ref> For example, amylose is responsible for causing white sauce to thicken, but, upon cooling, the solid and the water will partly separate. Amylose is known for its good film-forming properties, useful in food packaging. Excellent film-forming behavior of amylose was studied already in 1950s.<ref>{{cite journal |last1=Wolff |first1=Ivan A. |last2=Davis |first2=H. A. |last3=Cluskey |first3=J. E. |last4=Gundrum |first4=L. J. |last5=Rist |first5=Carl E. |title=Preparation of Films from Amylose |journal=Industrial & Engineering Chemistry |date=April 1951 |volume=43 |issue=4 |pages=915–919 |doi=10.1021/ie50496a039 }}</ref> Amylose films are better for both barrier properties<ref>{{cite journal |last1=Rindlav-Westling |first1=A˚sa |last2=Stading |first2=Mats |last3=Hermansson |first3=Anne-Marie |last4=Gatenholm |first4=Paul |title=Structure, mechanical and barrier properties of amylose and amylopectin films |journal=Carbohydrate Polymers |date=July 1998 |volume=36 |issue=2–3 |pages=217–224 |doi=10.1016/S0144-8617(98)00025-3 }}</ref> and mechanical properties when compared to the amylopectin films.<ref>{{cite journal |last1=Myllärinen |first1=Päivi |last2=Partanen |first2=Riitta |last3=Seppälä |first3=Jukka |last4=Forssell |first4=Pirkko |title=Effect of glycerol on behaviour of amylose and amylopectin films |journal=Carbohydrate Polymers |date=December 2002 |volume=50 |issue=4 |pages=355–361 |doi=10.1016/S0144-8617(02)00042-5 }}</ref>

In a laboratory setting, it can act as a marker. [[Iodine]] molecules fit neatly inside the [[helix|helical structure]] of amylose, binding with the starch polymer that absorbs certain known [[wavelengths]] of light. Hence, a common test is the [[iodine test]] for starch. If starch is mixed with a small amount of yellow iodine solution, a blue-black color will be observed. The intensity of the color can be tested with a [[Colorimeter (chemistry)|colorimeter]], using a red filter to discern the concentration of starch present in the solution. It is also possible to use [[starch indicator|starch as an indicator]] in titrations involving iodine reduction.<ref>{{cite web|url=http://dwb.unl.edu/Teacher/NSF/C10/C10Links/mills.edu/RESEARCH/FUTURES/JOHNB/structurefunction/722.html |title=Biochemistry Structure and Function |access-date=2010-05-25 |url-status=dead |archive-url=https://web.archive.org/web/20110927154547/http://dwb.unl.edu/Teacher/NSF/C10/C10Links/mills.edu/RESEARCH/FUTURES/JOHNB/structurefunction/722.html |archive-date=2011-09-27 }}</ref> It is also used in amylose magnetic beads and resin to separate [[maltose-binding protein]]<ref>{{cite web|url=http://www.neb.com/nebecomm/products/productE8035.asp |title=Amylose Magnetic Beads(E8035), pMAL Companion Products, NEB |access-date=2010-05-25 |url-status=dead |archive-url=https://web.archive.org/web/20100108151713/http://www.neb.com/nebecomm/products/productE8035.asp |archive-date=2010-01-08 }}</ref>

High-amylose varieties of [[rice]], the less sticky long-grain rice, have a much lower [[glycemic load]], which could be beneficial for [[diabetics]].<ref>{{Cite journal|last1=Juliano|first1=B. O.|last2=Perez|first2=C. M.|last3=Komindr|first3=S.|last4=Banphotkasem|first4=S.|date=December 1989|title=Properties of Thai cooked rice and noodles differing in glycemic index in noninsulin-dependent diabetics|journal=Plant Foods for Human Nutrition (Dordrecht, Netherlands)|volume=39|issue=4|pages=369–374|issn=0921-9668|pmid=2631091|doi=10.1007/bf01092074|s2cid=189939655}}</ref>

Researchers have identified the Granule Bound Starch Synthase (GBSS) as the enzyme that specifically elongates amylose during starch biosynthesis in plants.<ref name="annualreviews.org">{{cite journal | doi = 10.1146/annurev.food.102308.124214| pmid = 22129338| title = Biochemistry and Genetics of Starch Synthesis| journal = Annual Review of Food Science and Technology| volume = 1| pages = 271–303| year = 2010| last1 = Keeling| first1 = Peter L| last2 = Myers| first2 = Alan M}}</ref> The waxy locus in maize encodes for the GBSS protein.<ref name="annualreviews.org"/> Mutants lacking the GBSS protein produce starch containing only [[amylopectin]], such as in [[waxy corn]]. In Arabidopsis leaves, another gene, encoding the Protein Targeting to STarch (PTST) protein, is required in addition to GBSS for amylose synthesis. Mutants lacking either protein produce starch without amylose.<ref>{{cite journal | doi = 10.1371/journal.pbio.1002080| pmid = 25710501| pmc = 4339375| title = PROTEIN TARGETING TO STARCH is Required for Localising GRANULE-BOUND STARCH SYNTHASE to Starch Granules and for Normal Amylose Synthesis in Arabidopsis| journal = PLOS Biology| volume = 13| issue = 2| pages = e1002080| year = 2015| last1 = Seung| first1 = David| last2 = Soyk| first2 = Sebastian| last3 = Coiro| first3 = Mario| last4 = Maier| first4 = Benjamin A| last5 = Eicke| first5 = Simona| last6 = Zeeman| first6 = Samuel C| doi-access = free}}</ref> Genetically modified potato cultivar [[Amflora]] by [[BASF Plant Science]] was developed to not produce amylose.

* [[Amflora]], genetically modified low amylose potato (high in amylopectin)

* [[Amylomaize]], high amylose maize starch

* [[Russet Burbank potato]], high amylose potato cultivar

{{Commons category|Amylose}}

* {{cite journal | doi = 10.1021/jf051918i| pmid = 16536614| title = Rice Starch, Amylopectin, and Amylose: Molecular Weight and Solubility in Dimethyl Sulfoxide-Based Solvents| journal = Journal of Agricultural and Food Chemistry| volume = 54| issue = 6| pages = 2320–2326| year = 2006| last1 = Zhong| first1 = Fang| last2 = Yokoyama| first2 = Wallace| last3 = Wang| first3 = Qian| last4 = Shoemaker| first4 = Charles F}}

{{Carbohydrates}}

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