# Fructan
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{{Short description|Fructose polymer}}
[[Image:Inulin strukturformel.svg|thumb|class=skin-invert-image|right|250px|Structural formula of [inulin](/source/inulin)s, linear fructans with a terminal α-D-glucose with 1→2 linkage]]
A '''fructan''' is a [polymer](/source/polymer) of [fructose](/source/fructose) molecules. Fructans with a short chain length are known as [fructooligosaccharide](/source/fructooligosaccharide)s. Fructans can be found in over 12% of the [angiosperm](/source/angiosperm)s including both [monocots](/source/monocots) and [dicots](/source/dicotyledon)[{{Cite journal|last=Hendry|first=George|date=1987|title=The Ecological Significance of Fructan in a Contemporary Flora|journal=New Phytologist|language=en|volume=106|issue=s1|pages=201–216|doi=10.1111/j.1469-8137.1987.tb04690.x|issn=1469-8137|doi-access=free}}] such as [agave](/source/agave), [artichoke](/source/artichoke)s, [asparagus](/source/asparagus), [leek](/source/leek_(vegetable))s, [garlic](/source/garlic), [onion](/source/onion)s (including [spring onion](/source/spring_onion)s), [yacón](/source/yac%C3%B3n), [jícama](/source/j%C3%ADcama), [barley](/source/barley) and [wheat](/source/wheat).
Fructans also appear in [grass](/source/grass), with [dietary implications](/source/Laminitis) for horses and other grazing animals ([Equidae](/source/Equidae)).
==Types==
Fructans are built up of fructose residues, normally with a [sucrose](/source/sucrose) unit (i.e. a [glucose](/source/glucose)–fructose [disaccharide](/source/disaccharide)) at what would otherwise be the reducing terminus. The linkage position of the fructose residues determine the type of the fructan. There are five types of fructans.[{{cite book |chapter=Carbohydrate Metabolism |first1=R. N. |last1=Chibbar |first2=S. |last2=Jaiswal |first3=M. |last3=Gangola |first4=M. |last4=Båga |doi=10.1016/B978-0-08-100596-5.00089-5 |title=Reference Module in Food Science |date=2016 |chapter-url=https://www.sciencedirect.com/topics/agricultural-and-biological-sciences/campanulales |quote=Fructans, on the basis of glycosidic linkage, are categorized into five groups: (a) inulin having β(2 → 1) linkage, (b) levan/phlein having β(2 → 6) linkage, (c) graminin (having inulin or levan backbone with ≥ 1 short branch), (d) inulin neoseries (like inulin but one glucose unit between two fructose moieties), and (e) levan neoseries (like levan but one glucose unit between two fructose moieties) (Figure 1).|isbn=9780081005965 }}]
Linkage normally occurs at one of the two primary [hydroxyl](/source/hydroxyl)s ([OH-1](/source/OH-1_(compound)) or [OH-6](/source/OH-6_(compound))), and there are two basic types of simple fructan:
* 1-linked: in [inulin](/source/inulin), the fructosyl residues are linked by β-2,1-linkages
* 6-linked: in [levan](/source/levan_polysaccharide) and [phlein](/source/phlein), the fructosyl residues are linked by β-2,6-linkages
A third type of fructans, the graminin type,[{{Cite journal | doi = 10.3389/fpls.2013.00247| pmid = 23882273| pmc = 3713406| title = Multifunctional fructans and raffinose family oligosaccharides| journal = Frontiers in Plant Science| volume = 4| pages = 247| year = 2013| last1 = Van den Ende | first1 = Wim| doi-access = free}}]
Two more types of fructans are more complex: they are formed on a 6G-[kestotriose](/source/kestotriose) backbone where elongations occur on both sides of the molecule. Again two types are discerned:
* neo-inulin type (also called "inulin neoseries"[{{Cite journal | last1 = Pollock | first1 = C. J. | doi = 10.1111/j.1469-8137.1986.tb00629.x | title = Tansley Review No. 5 Fructans and the Metabolism of Sucrose in Vascular Plants | journal = New Phytologist | volume = 104 | pages = 1–24| year = 1986 | issue = 1 | pmid = 33873815 | doi-access = | s2cid = 84222488 }}][{{Cite journal | last1 = Pollock | first1 = C. J. | last2 = Cairns | first2 = A. J. | doi = 10.1146/annurev.pp.42.060191.000453 | title = Fructan Metabolism in Grasses and Cereals | journal = Annual Review of Plant Physiology and Plant Molecular Biology | volume = 42 | pages = 77–101 | year = 1991 }}] A notable exception is [rice](/source/rice), which is unable to synthesise fructans.[{{Cite journal | last1 = Kawakami | first1 = A. | last2 = Sato | first2 = Y. | last3 = Yoshida | first3 = M. | doi = 10.1093/jxb/erm367 | title = Genetic engineering of rice capable of synthesizing fructans and enhancing chilling tolerance | journal = Journal of Experimental Botany | volume = 59 | issue = 4 | pages = 793–802 | year = 2008 | pmid = 18319240| doi-access = free }}]
In barley, fructan accumulates in the cell [vacuoles](/source/vacuole) and acts as a [carbon sink](/source/carbon_sink) within the cell to facilitate photosynthesis. Fructan reserves are transported to the reproductive tissue during grain filling, and to the vegetative tissues during periods of growth.{{cn|date=May 2020}}
Chicory [inulin-type fructans](/source/Inulin) are used mainly as the raw materials for industrial production of fructans as food ingredients. Use in the food industry is based on the nutritional and technological properties of fructans as a [prebiotic](/source/Prebiotic_(nutrition)) [dietary fiber](/source/dietary_fiber).[{{Cite journal|last1=Meyer|first1=D.|last2=Bayarri|first2=S.|last3=Tárrega|first3=A.|last4=Costell|first4=E.|date=2011-12-01|title=Inulin as texture modifier in dairy products|journal=Food Hydrocolloids|series=25 years of Advances in Food Hydrocolloid Research|volume=25|issue=8|pages=1881–1890|doi=10.1016/j.foodhyd.2011.04.012|issn=0268-005X}}][{{Citation|last=Tungland|first=Bryan|title=Chapter 8 - Nondigestible Fructans as Prebiotics|date=1 June 2018|work=Human Microbiota in Health and Disease|pages=349–379|editor-last=Tungland|editor-first=Bryan|publisher=Academic Press|doi=10.1016/b978-0-12-814649-1.00008-9|isbn=9780128146491}}]
==Fructan content of various foods==
{| class=wikitable
|[Agave](/source/Agave)
|7–25%[{{cite journal | last1 = Shepherd | first1 = Susan J. | year = 2006 | title = Fructose Malabsorption and Symptoms of Irritable Bowel Syndrome: Guidelines for Effective Dietary Management | url = http://sacfs.asn.au/download/SueShepherd_sarticle.pdf | journal = J Am Diet Assoc | volume = 106 | issue = 10 | pages = 1631–1639 | doi = 10.1016/j.jada.2006.07.010 | pmid = 17000196 | access-date = 2007-12-05 | archive-date = 2011-03-14 | archive-url = https://web.archive.org/web/20110314222733/http://sacfs.asn.au/download/SueShepherd_sarticle.pdf | url-status = dead }}]
|-
||[Globe artichoke](/source/Globe_artichoke)||2.0–6.8%[{{cite journal | last1 = Slavin | first1 = Joanne L. | year = 2000 | title = Mechanisms for the Impact of Whole Grain Foods on Cancer Risk | url = http://www.jacn.org/cgi/content/full/19/suppl_3/300S | journal = Journal of the American College of Nutrition | volume = 19 | issue = 90003| pages = 300S–307S | doi = 10.1080/07315724.2000.10718964 | pmid = 10875601 | s2cid = 43665952 | url-access = subscription }}]
|-
||[Garlic](/source/Garlic)||17.4%[{{cite journal | author = Muir, J.G. | year = 2007| title = Fructan and Free Fructose Content of Common Australian Vegetables and Fruit | journal = Journal of Agricultural and Food Chemistry | volume = 55 | issue = 16| pages = 6619–6627 | doi = 10.1021/jf070623x |display-authors=etal | pmid=17625872}}]
|-
||[Onion](/source/Onion)||1.1–10.1%[Karppinen, Sirpa. Dietary fibre components of rye bran and their fermentation in vitro. Espoo 2003. VTT Publications 500. 96 p. + app. 52 p.[http://www.vtt.fi/inf/pdf/publications/2003/P500.pdf]]
|-
||[Rye (grain)](/source/Rye)||4.6–6.6%