Gluten (from Latin gluten, "glue") is a protein composite found in foods processed from wheat and related grain species, including barley, rye, and spelt. Gluten gives elasticity to dough, helping it rise and keep its shape and often gives the final product a chewy texture. Gluten is used in cosmetics, hair products, and other dermatological preparations.
Gluten is the composite of a gliadin and a glutenin, which is conjoined with starch in the endosperm of various grass-related grains. The prolamin and glutelin from wheat (gliadin, which is alcohol-soluble, and glutenin, which is only soluble in dilute acids or alkalis) constitute about 80% of the protein contained in wheat fruit. 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 fruit 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 true gluten.
Gluten is extracted from flour by kneading the flour, agglomerating the gluten into an elastic network, a dough, and then washing out the starch. Starch granules disperse in cold water, and the dispersed starch will be sedimented and dried. If a saline solution is used instead of water, a purer protein is obtained, with certain harmless impurities going into solution with the starch. Where starch is the prime product, cold water is the favored solvent because the impurities stay with the gluten.
In home or restaurant cooking, a ball of wheat flour dough is kneaded under water until the starch disperses out. In industrial production, a slurry of wheat flour is kneaded vigorously by machinery until the gluten agglomerates into a mass. This mass is collected by centrifugation, then transported through several stages integrated in a continuous process. Approximately 65% of the water in the wet gluten is removed by means of a screw press; the remainder is sprayed through an atomizer nozzle into a drying chamber, where it remains at an elevated temperature a short time to evaporate the water without denaturing the gluten. The process yields a flour-like powder with a 7% moisture content, which is air cooled and pneumatically transported to a receiving vessel. In the final step, the collected gluten is sifted and milled to produce a uniform product.
Gluten forms when glutenin molecules cross-link to form a sub-microscopic network attached to gliadin, which contributes viscosity (thickness) and extensibility to the mix. If this dough is leavened with yeast, fermentation produces carbon dioxide bubbles, which, trapped by the gluten network, cause the dough to 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 through hydration.
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 as this portion contains the preponderance of the sulfur atoms responsible for the cross-linking in the network. More refining (of the gluten) leads to chewier products such as pizza and bagels, while less refining yields tender baked goods such as pastry products.
Generally, bread flours are high in gluten (hard wheat); pastry flours have a lower gluten content. Kneading promotes the formation of gluten strands and cross-links, creating baked products that are chewier in proportion to the length of kneading. An increased moisture content in the dough enhances gluten development, and very wet doughs left to rise for a long time require no kneading (see no-knead bread). Shortening inhibits formation of cross-links and is used, along with diminished water and less kneading, when a tender and flaky product, such as a pie crust, is desired.
The strength and elasticity of gluten in flour is measured in the baking industry using a farinograph. This gives the baker a measurement of quality for different varieties of flours in developing recipes for various baked goods.
Gluten, when dried and milled to a powder and added to ordinary flour dough, improves a dough's ability to rise and increases the bread's structural stability and chewiness. Gluten-added dough must be worked vigorously to induce it to rise to its full capacity; an automatic bread machine or food processor may be required for kneading. The added gluten provides supplemental protein to products with low or nonexistent protein levels.
Gluten, especially wheat gluten, is often the basis for imitation meats resembling beef, chicken, duck (see mock duck), fish, and pork. When cooked in broth, gluten absorbs some of the surrounding liquid (including the taste) and becomes firm to the bite.
Added to other foods
Gluten is often present in beer and soy sauce, and can be used as a stabilizing agent in more unexpected food products, such as ice cream and ketchup. Foods of this kind raise a problem, because the hidden gluten constitutes a hazard for people with celiac disease.
Gluten is known to cause adverse health problems in those who suffer from gluten sensitivity, primarily as a result of coeliac disease (spelled "celiac" in American English); whether non-coeliac sources of gluten sensitivity exist remains controversial. In 2009 research showed between 0.5 and 1.0 percent of people in the US and UK are sensitive to gluten due to coeliac disease, which constitutes an abnormal immune reaction to partially digested gliadin. It probably occurs with comparable frequencies among all wheat-eating populations in the world. Coeliac disease has no cure but is manageable with a gluten-free diet. Wheat allergy and celiac disease are different disorders.
International Labeling Standards
Labeling in Canada
Labels for all food products sold in Canada must clearly identify the presence of gluten if it is present at a level greater than 10 ppm.
Labeling in the UK
In the United Kingdom, only cereals must be labelled; labelling of other products is voluntary.
Labeling in the US
In the United States, gluten might not be listed on labels, because the US Food and Drug Administration (FDA) has historically classified gluten as GRAS ("generally recognized as safe"). Stricter requirements for proper labeling of gluten content are being formulated by the FDA. In August 2013, FDA issued a final rule to define the term “gluten-free” for voluntary use in the labeling of foods i.e. "presence of gluten in the food must be less than 20 ppm."
- Harding, Anne (31 October 2011). "Gluten in cosmetics may pose hidden threat to celiac patients". CNN Health. Retrieved 21 October 2012.
- "Gluten intolerance rising in developed countries". Journal Sentinel (Milwaukee). 27 June 2010. Retrieved 5 July 2013.
- "Extracting Gluten from Flour". Chaos – it's not just a theory…. 20 June 2010. Retrieved 21 October 2012.
- "Wheat Starch and Wheat Gluten". GEA Westfalia Separator Group. Retrieved 19 October 2011.
- "Wheat". GEA Barr-Rosin. Retrieved 8 September 2009.
- Woychick, JH; et al. "The Gluten Proteins and Deamidated Soluble Wheat Protein". Retrieved 8 September 2009.
- 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 analysis.
- Edwards, N. M.; Mulvaney, S. J.; Scanlon, M. G.; Dexter, J. E. (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.
- Tosi, Paola; Masci, Stefania; Giovangrossi, Angela2; D'Ovidio, Renato; Bekes, Frank; Larroque, Oscar; Napier, Johnathan; Shewry, Peter (September 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.
- "Baking Technology, Bread". Bakersassist. Retrieved 2007-08-14.
- Amendola, J.; Rees, N.; & Lundberg, D. E. (2002). Understanding Baking.
- Eckhardt, L.W. & Butts, D.C. (1997). Rustic European Breads from your Bread Machine.
- "What Does Gluten-Free Mean?". Spiritfoods. Retrieved 21 October 2012.
- A Harvard teaching hospital. "Following a Gluten-free Diet". Beth Israel Deaconess Medical Center.[dead link]
- "Pet Foods". International Wheat Gluten Association. Archived from the original on 2007-10-07. Retrieved 14 August 2007.
- Biesiekierski JR et al. No Effects of Gluten in Patients With Self-Reported Non-Celiac Gluten Sensitivity After Dietary Reduction of Fermentable, Poorly Absorbed, Short-Chain Carbohydrates. Gastroenterology. 2013;145(2):320-328
- "Celiac Disease". National Digestive Diseases Information Clearing House. National Institutes of Health (NIH). 2004. Retrieved 8 September 2009.
- "Celiac disease". Consensus Development Panel on Celiac Disease. National Institutes of Health (NIH). 2005. Retrieved 2007-08-14.
- "Coeliac Disease". What is coeliac disease?. Coeliac UK. Retrieved 18 April 2013.
- 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.
- "Food intolerance and coeliac disease" (PDF). Food Standards Agency. September 2006. Retrieved 8 September 2009.
- "Codex Standard For "Gluten-Free Foods" CODEX STAN 118-1981" (PDF). Codex Alimentarius. February 22, 2006.
- Canadian Celiac Association
- "Guidance Notes on the Food Labelling (Amendment) (No. 2) Regulations 2004" (PDF). Food Standards Agency. November 2005.
- Curtis, B.C.; Rajaram, S.; Macpherson, H.G. "Bread Wheat, Improvement and production — FAO Plant Production and Protection Series No. #30.". Retrieved 2007-08-21.
- Pfluger, Laura. "Marker Assisted Selection in Wheat, Quality traits. Gluten Strength, Coordinated Agricultural Project (funded by USDACREES)". Retrieved 2007-09-29.
- = 11017 Agricultural Databases, Statistics, etc.. USDA Cereal Disease Laboratory. Retrieved 2007-08-21.
- Wieser, H. (2007). Cereal Chemistry and Dough Properties, KL1-Gluten Chemistry. German Research Centre of Food Chemistry and Cereal Chemistry and Hans-Dieter-Belitz-Institute for Cereal Grain Research, D-85748 Garching, Germany. Retrieved 2007-09-27.
- Wrigley, C.W; Bekes, F.; Bushuk, W (2006). The Gluten Composition of Wheat Varieties and Genotypes. AACC International. ISBN 1-891127-51-9. Retrieved 2007-09-21.