Gluten

Gluten is a structural protein complex naturally found in certain cereal grains. The term gluten usually refers to the elastic network of a wheat grain's proteins, gliadin and glutenin primarily, which forms readily with the addition of water and often kneading in the case of bread dough. The types of grains that contain gluten include all species of wheat (common wheat, durum, spelt, khorasan, emmer, and einkorn), barley, rye, and some cultivars of oat; moreover, cross hybrids of any of these cereal grains also contain gluten, e.g. triticale. Gluten makes up 75–85% of the total protein in bread wheat. Glutens, especially Triticeae glutens, have unique viscoelastic and adhesive properties, which give dough its elasticity, helping it rise and keep its shape and often leaving the final product with a chewy texture. These properties, and its relatively low cost, make gluten valuable to both food and non-food industries. Wheat gluten is composed of mainly two types of proteins: the glutenins and the gliadins, which in turn can be divided into high molecular and low molecular glutenins and α/β, γ and Ω gliadins. Its homologous seed storage proteins, in barley, are referred to as hordeins, in rye, secalins, and in oats, avenins. These protein classes are collectively referred to as "gluten". The storage proteins in other grains, such as maize (zeins) and rice (rice protein), are sometimes called gluten, but they do not cause harmful effects in people with celiac disease.

Gluten can trigger adverse inflammatory, immunological, and autoimmune reactions in some people. The spectrum of gluten related disorders includes celiac disease in 1–2% of the general population, non-celiac gluten sensitivity in 0.5–13% of the general population, as well as dermatitis herpetiformis, gluten ataxia and other neurological disorders. These disorders are treated by a gluten-free diet.

Uses

Bread products Gluten forms when glutenin molecules cross-link via disulfide bonds to form a submicroscopic 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 contributing as a factor in the staling of bread, possibly because it binds water through hydration.

The formation of gluten 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 gluten network. Using flour with higher gluten content leads to chewier doughs such as those found in pizza and bagels, while using flour with less gluten content 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 (as opposed to more brittle or crumbly). The "chewiness" increases as the dough is kneaded for longer. 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 when developing recipes for various baked goods.

Added gluten 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. About 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 for a short time to allow the water to evaporate 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 processed gluten is sifted and milled to produce a uniform product. This flour-like powder, when added to ordinary flour dough, may help improve the dough's ability to increase in volume. The resulting mixture also 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 high-gluten kneading. Generally, higher gluten levels are associated with higher overall protein content.

Imitation meats

Gluten, especially wheat gluten (seitan), 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 flavor) and becomes firm to the bite. This use of gluten is a popular means of adding supplemental protein to many vegetarian diets. In home or restaurant cooking, wheat gluten is prepared from flour by kneading the flour under water, agglomerating the gluten into an elastic network known as a dough, and then washing out the starch.

Other consumer products 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 may therefore present problems for a small number of consumers because the hidden gluten constitutes a hazard for people with celiac disease and gluten sensitivities. The protein content of some pet foods may also be enhanced by adding gluten. Gluten is also used in cosmetics, hair products and other dermatological preparations.

Animal feed Wheat gluten is used both as a protein source and binding ingredient in pet foods. Wheat gluten imported from China adulterated with melamine used in pet foods was considered to have caused harm in many countries in 2007.

Disorders

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