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Gluten

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This is an old revision of this page, as edited by Njál (talk | contribs) at 19:35, 12 September 2010 (edit introduces more jargon, but the statement that gliadin and glutenin are found in rye/barley is erroneous, and not to consider rye/barley on the same level as wheat would be misleading). The present address (URL) is a permanent link to this revision, which may differ significantly from the current revision.

For the food products made from gluten see Wheat gluten (food).
Wheat seed, sectioned to reveal endosperm and embryo
Wheat, a prime source of gluten

Gluten (from Latin gluten "glue") is the composite of a prolamin and a glutelin. These exist, conjoined with starch, in the endosperm of some grass-related grains, notably wheat, rye, and barley. Gliadin and glutenin (the prolamin and glutelin from wheat) comprise about 80% of the protein contained in wheat seed. Being insoluble in water, they can be purified by washing away the associated starch. Worldwide, gluten is a source of protein, both in foods prepared directly from sources containing it, and as an additive to foods otherwise low in protein.

The seeds of most flowering plants have endosperms with stored protein to nourish embryonic plants during germination. True gluten, with gliadin and glutenin, is limited to certain members of the grass family. The stored proteins of maize and rice are sometimes called glutens, but their proteins differ from wheat gluten by lacking gliadin. The glutenin in wheat flour gives kneaded dough its elasticity, allows leavening and contributes chewiness to baked products like bagels.

Extraction

Gluten is extracted from flour by washing out the starch: starch is water soluble while gluten is not, and gluten binds together strongly, while starch dissolved in cold water is mobile. If a saline solution is used instead of water, a purer protein is obtained, with certain harmless impurities going into solution with the starch. However, on an industrial scale, starch is the prime product, so cold water is the favored solvent. To effect the separation, a slurry of wheat flour is stirred vigorously by machinery until the starch dissolves and the gluten consolidates into a mass, which is collected by centrifugation, then carried, by complex machinery, through several stages combined into a continuous process. Approximately 65% of the water in the wet gluten is removed by means of a screw press, and the residue is sprayed through an atomizer nozzle into a drying chamber, where it remains at an elevated temperature only long enough to evaporate the water without denaturing the gluten. This yields a flour-like powder with a 7% moisture content, which is quickly air cooled and pneumatically transported to a receiving vessel. In the final step, the collected gluten is sifted and milled to make the product uniform.[1]

Uses

Fried gluten balls

Bread products

When dough made with wheat flour is kneaded, gluten forms as glutenin molecules cross-link to make a sub-microscopic network and associates with gliadin, which contributes viscosity (thickness) and extensibility to the mix.[2] If such dough is leavened with yeast, sugar fermentation produces bubbles of carbon dioxide which, trapped by the gluten network, cause the dough to swell or rise. Baking coagulates the gluten, which, along with starch, stabilizes the shape of the final product. Gluten content has been implicated as a factor in the staling of bread, possibly because it binds water by hydration.[3]

The development of gluten (i.e., enhancing its elasticity) affects the texture of the baked goods. Gluten's attainable elasticity is proportional to its content of glutenins with low molecular weights because that fraction contains the preponderance of the sulfur atoms responsible for the cross-linking in the network.[4][5] More development leads to chewier products like pizza and bagels, while less development yields tender baked goods. In general, bread flours are high in gluten while cake flours are low. Kneading promotes the formation of gluten strands and cross-links, so a baked product is chewier in proportion to how much the dough is worked. Increased wetness of the dough also enhances gluten development.[6] Shortening inhibits formation of cross-links, so it is used, along with diminished water and minimal working, when a tender and flaky product, such as pie crust, is desired.

Added gluten

Gluten, when dried and milled to powder and added to ordinary flour dough, improves rising and increases the bread's structural stability and chewiness.[7] Such doughs must be worked vigorously if they are to rise to their full capacity, so a bread machine or food processor may be required for their kneading.[8] The added gluten provides supplemental protein to what would otherwise be high-carbohydrate preparations.

Imitation meats

Gluten, especially wheat gluten, is the basis for imitation meats resembling chicken, duck (mock duck), fish, pork and beef. The Japanese forms are called namafu, yakifu, and seitan. When cooked in broth, gluten absorbs some of the surrounding liquid (including the taste) and becomes firm to the bite, so is widely used in vegetarian, vegan and Buddhist cuisines as a meat substitute.

Added to other foods

The "Codex Alimentarius" set of international standards for food labeling has a standard relating to the labelling of products as "gluten free", however this standard does not apply to "foods which in their normal form do not contain gluten".[9] Gluten is used as a stabilizing agent in products like ice cream and ketchup, where it may be unexpected.[10][11] Foods of this kind present a problem because the hidden gluten constitutes a hazard for people with celiac disease: In the United States, at least, gluten might not be listed on the labels of such foods because the U.S, Food and Drug Administration has classified gluten as GRAS (generally recognized as safe).[12] Requirements for proper labeling are being formulated by the USDA. In the United Kingdom, only cereals currently need to be labelled, while other products are voluntary.[13]

Pet foods

The protein content of some pet foods may also be enhanced by adding gluten.[14]

Adverse reactions

Main articles: Gluten sensitivity and Gluten-free diet

Between 0.5 and 1.0 percent of people in the United States are sensitive to gluten due to coeliac disease.[15][16] Coeliac disease is caused by an abnormal immune reaction to partially digested gliadin. It probably occurs with comparable frequencies among all wheat-eating populations in the world.[17] Certain allergies and neuropathies are also caused by gluten consumption and inhalation.[citation needed][18]

Note that wheat allergy and celiac disease are different disorders.[19]

See also

References

  1. ^ "Wheat". GEA Barr-Rosin. Retrieved 8 September 2009.
  2. ^ Woychick, JH; et al. "The Gluten Proteins and Deamidated Soluble Wheat Protein (SWP)". Retrieved 8 September 2009. {{cite web}}: Explicit use of et al. in: |author2= (help)
  3. ^ Sahlstrom, S. & Brathen, E. (1997). Effects of enzyme preparations for baking, mixing time and resting time on bread quality and bread staling. Food Chemistry, 58, 1, 75-80. Effects of wheat variety and processing conditions in experimental bread baking studied by univariate and multivariate analyses.
  4. ^ Edwards, N. M. (2003). "Role of gluten and its components in determining durum semolina dough viscoelastic properties". Cereal chemistry. 80 (6): 755–763. doi:10.1094/CCHEM.2003.80.6.755. Retrieved 2007-08-14. {{cite journal}}: Unknown parameter |coauthors= ignored (|author= suggested) (help)
  5. ^ Tosi, Paola (2005). "Modification of the Low Molecular Weight (LMW) Glutenin Composition of Transgenic Durum Wheat: Effects on Glutenin Polymer Size and Gluten Functionality". Molecular Breeding. 16 (2): 113–126. doi:10.1007/s11032-005-5912-1. Retrieved 2007-08-14. {{cite journal}}: Unknown parameter |coauthors= ignored (|author= suggested) (help); Unknown parameter |month= ignored (help); line feed character in |coauthors= at position 109 (help); line feed character in |title= at position 107 (help)
  6. ^ "Baking Technology, Bread". Bakersassist. Retrieved 2007-08-14.
  7. ^ Amendola, J., Rees, N., & Lundberg, D. E. (2002). Understanding Baking
  8. ^ Echkardt, LW & Butts, DC. (1997). Rustic European Breads from your Bread Machine
  9. ^ "Codex Standard For "Gluten-Free Foods" CODEX STAN 118-1981" (PDF). Codex Alimentarius. February 22, 2006.
  10. ^ Pat Kendall, Ph.D., R.D. (March 31, 2003). "Gluten sensitivity more widespread than previously thought". Colorado State University Extension.{{cite web}}: CS1 maint: multiple names: authors list (link)
  11. ^ "Following a Gluten-free Diet". Beth Israel Deaconess Medical Center. A Harvard teaching hospital. {{cite web}}: Check date values in: |date= (help)
  12. ^ "Sec. 184.1322 Wheat gluten". Code of Federal Regulations Center. April 1, 2007.
  13. ^ "Guidance Notes on the Food Labelling (Amendment) (No. 2) Regulations 2004" (PDF). Food Standards Agency. 2005. {{cite web}}: Unknown parameter |month= ignored (help)
  14. ^ "Pet Foods". International Wheat Gluten Association. Retrieved 2007-08-14.
  15. ^ "Celiac Disease". National Digestive Diseases Information Clearing House. National Institutes of Health (NIH). 2004. Retrieved 8 September 2009.
  16. ^ "Celiac disease". Consensus Development Panel on Celiac Disease. National Institutes of Health (NIH). 2005. Retrieved 2007-08-14.
  17. ^ van Heel D, West J (2006). "Recent advances in coeliac disease". Gut. 55 (7): 1037–46. doi:10.1136/gut.2005.075119. PMC 1856316. PMID 16766754.
  18. ^ David A. Nelsen. "Gluten Sensitive Enteropathy". Retrieved 2007-08-14.
  19. ^ "Food intolerance and coeliac disease" (PDF). Food Standards Agency. 2006. Retrieved 8 September 2009. {{cite web}}: Unknown parameter |month= ignored (help)

Further reading

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