Structural formula of inulins, linear fructans with a terminal α-D-glucose with 1→2 linkage

A fructan is a polymer of fructose molecules. Fructans with a short chain length are known as fructooligosaccharides. Fructans can be found in over 12% of the angiosperms including both monocots and dicots[1] such as agave, artichokes, asparagus, leeks, garlic, onions (including spring onions), yacón, jícama, barley and wheat.

Fructans also appear in grass, with dietary implications for horses and other grazing animals (Equidae).

Types

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.[2]

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,[2] contains both β-2,1-linkages and β-2,6-linkages.[3]

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

Functions

Fructans are important storage polysaccharides in the stems of many species of grasses and confer a degree of freezing tolerance.[4][5] A notable exception is rice, which is unable to synthesise fructans.[6]

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.

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.[7][8]

Fructan content of various foods

Agave 7–25%[8]
Jerusalem artichoke16.0–20.0%[9]
Globe artichoke2.0–6.8%[9]
Asparagus1.4–4.1%[9]
Barley kernels (very young)22%[10]
Garlic17.4%[11]
Onion1.1–10.1%[9]
Rye (bran)7%[12]
Rye (grain)4.6–6.6%[12]
Wheat bread (white)0.7–2.8%[9]
Wheat flour1–4%[10]
Wheat pasta1–4%[9]

See also

Look up fructan in Wiktionary, the free dictionary.

Notes

  1. ↑ Hendry, George (1987). "The Ecological Significance of Fructan in a Contemporary Flora". New Phytologist. 106 (s1): 201–216. doi:10.1111/j.1469-8137.1987.tb04690.x. ISSN 1469-8137.
  2. 1 2 3 4 Chibbar, R. N.; Jaiswal, S.; Gangola, M.; Båga, M. (2016). "Carbohydrate Metabolism". Reference Module in Food Science. doi:10.1016/B978-0-08-100596-5.00089-5. ISBN 9780081005965. 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).
  3. ↑ Van den Ende, Wim (2013). "Multifunctional fructans and raffinose family oligosaccharides". Frontiers in Plant Science. 4: 247. doi:10.3389/fpls.2013.00247. PMC 3713406. PMID 23882273.
  4. ↑ Pollock, C. J. (1986). "Tansley Review No. 5 Fructans and the Metabolism of Sucrose in Vascular Plants". New Phytologist. 104 (1): 1–24. doi:10.1111/j.1469-8137.1986.tb00629.x. PMID 33873815. S2CID 84222488.
  5. ↑ Pollock, C. J.; Cairns, A. J. (1991). "Fructan Metabolism in Grasses and Cereals". Annual Review of Plant Physiology and Plant Molecular Biology. 42: 77–101. doi:10.1146/annurev.pp.42.060191.000453.
  6. ↑ Kawakami, A.; Sato, Y.; Yoshida, M. (2008). "Genetic engineering of rice capable of synthesizing fructans and enhancing chilling tolerance". Journal of Experimental Botany. 59 (4): 793–802. doi:10.1093/jxb/erm367. PMID 18319240.
  7. ↑ Meyer, D.; Bayarri, S.; Tárrega, A.; Costell, E. (2011-12-01). "Inulin as texture modifier in dairy products". Food Hydrocolloids. 25 years of Advances in Food Hydrocolloid Research. 25 (8): 1881–1890. doi:10.1016/j.foodhyd.2011.04.012. ISSN 0268-005X.
  8. 1 2 Tungland, Bryan (1 June 2018), Tungland, Bryan (ed.), "Chapter 8 - Nondigestible Fructans as Prebiotics", Human Microbiota in Health and Disease, Academic Press, pp. 349–379, doi:10.1016/b978-0-12-814649-1.00008-9, ISBN 9780128146491
  9. 1 2 3 4 5 6 Shepherd, Susan J. (2006). "Fructose Malabsorption and Symptoms of Irritable Bowel Syndrome: Guidelines for Effective Dietary Management" (PDF). J Am Diet Assoc. 106 (10): 1631–1639. doi:10.1016/j.jada.2006.07.010. PMID 17000196.
  10. 1 2 Slavin, Joanne L. (2000). "Mechanisms for the Impact of Whole Grain Foods on Cancer Risk". Journal of the American College of Nutrition. 19 (90003): 300S–307S. doi:10.1080/07315724.2000.10718964. PMID 10875601. S2CID 43665952.
  11. ↑ Muir, J.G.; et al. (2007). "Fructan and Free Fructose Content of Common Australian Vegetables and Fruit". Journal of Agricultural and Food Chemistry. 55 (16): 6619–6627. doi:10.1021/jf070623x. PMID 17625872.
  12. 1 2 Karppinen, Sirpa. Dietary fibre components of rye bran and their fermentation in vitro. Espoo 2003. VTT Publications 500. 96 p. + app. 52 p.

References

  • 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
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