Gluten

Gluten (from Latin gluten, 'glue') is a group of proteins, called prolamins and glutelins, which occur with starch in the endosperm of various cereal grains. This protein complex comprises 75–85% of the total protein in bread wheat. It is found in related wheat species and hybrids, (such as spelt, khorasan, emmer, einkorn, and triticale), barley, rye, and oats, as well as products derived from these grains, such as breads and malts. Gluten (from Latin gluten, 'glue') is a group of proteins, called prolamins and glutelins, which occur with starch in the endosperm of various cereal grains. This protein complex comprises 75–85% of the total protein in bread wheat. It is found in related wheat species and hybrids, (such as spelt, khorasan, emmer, einkorn, and triticale), barley, rye, and oats, as well as products derived from these grains, such as breads and malts. 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 relative low cost are the reasons why gluten is so widely demanded by the food industry and for non-food uses. Prolamins in wheat are called gliadins; in barley, hordeins; in rye, secalins; and in oats, avenins. These protein classes are collectively referred to as gluten. Wheat glutelins are called glutenin. True gluten is limited to these four grains. (The storage proteins in maize and rice are sometimes called glutens, but they differ from true gluten.) Gluten can trigger adverse inflammatory, immunological and autoimmune reactions in some people. Gluten can produce a broad spectrum of gluten-related disorders, including coeliac disease in 1–2% of the general population, non-coeliac gluten sensitivity in 6–10% of the general population, dermatitis herpetiformis, gluten ataxia and other neurological disorders. These disorders are treated by a gluten-free diet. 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 implicated 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.Further refining of the gluten leads to chewier doughs such as those found in 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 (as opposed to more brittle or crumbly). The 'chewiness' increases as the dough is kneaded for longer times. 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. 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.