fructan

Fructans are built up of fructose residues, normally with a sucrose unit (i.e. a glucose–fructose 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 hydroxyls (OH-1 or OH-6), and there are two basic types of simple fructan:

• 1-linked: in inulin, the fructosyl residues are linked by β-2,1-linkages
• 6-linked: in levan and phlein, the fructosyl residues are linked by β-2,6-linkages

A third type of fructans, the graminin type, contains both β-2,1-linkages and β-2,6-linkages.{{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 backbone where elongations occur on both sides of the molecule. Again two types are discerned:

• neo-inulin type (also called "inulin neoseries"): predominant β-2,1-linkages
• neo-levan type (also called "levan neoseries"): predominant β-2,6-linkages

Fructans are important storage polysaccharides in the stems of many species of grasses and confer a degree of freezing tolerance.{{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, 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 and acts as a 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 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 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}}

{{Wiktionary}}

• {{annotated link|Dietary fiber}}
• {{annotated link|Prebiotic (nutrition)}}

{{reflist}}

• Sugar – Chemical, Biological and Nutritional Aspects of Sucrose. John Yudkin, Jack Edelman and Leslie Hough (1971, 1973). The Butterworth Group. {{ISBN|0-408-70172-2}}

{{Carbohydrates}}

Category:Polysaccharides

Category:Prebiotics (nutrition)

Category:Fructosides