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Friday March 24th 2017

Allergy Info > Gluten

Gluten (from Latin gluten “glue”) is a protein composite that appears in foods processed from wheat and related species, including barley and rye. It gives elasticity to dough, helping it to rise and to keep its shape, and often giving the final product a chewy texture.

As cases of known gluten sensitivity increase, many foods in the western world are now labeled to clarify whether they contain gluten.

Gluten is the composite of a prolamin and a glutelin, which exist, conjoined with starch, in the endosperm of various grass-related grains. Gliadin, a water-soluble, and glutenin, a water-insoluble, (the prolamin and glutelin from wheat) compose 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.

 

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, making cold water the favored solvent.

In home or restaurant cooking, a ball of wheat flour dough is kneaded under water until the starch dissolves out. In industrial production, a slurry of wheat flour is kneaded vigorously by machinery until the starch dissolves and the gluten condenses 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.[1]

Gluten forms as glutenin molecules cross-link to form a sub-microscopic network attached to gliadin, which contributes viscosity (thickness) and extensibility to the mix.[2] If this dough is leavened with yeast, sugar fermentation produces bubbles of carbon dioxide 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.[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 as this portion contains the preponderance of the sulfur atoms responsible for the cross-linking in the network.[4][5] 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; cake flours have a lower gluten content. Kneading promotes the formation of gluten strands and cross-links, creating baked product that is chewier in proportion to the length of kneading. An increased moisture content in the dough enhances gluten development.[6] 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.

Added gluten

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.[7] 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.[8] The added gluten provides supplemental protein to products with low or nonexistent protein levels.

Imitation meats

For more details on the use of gluten in cooking, see Wheat gluten (food).

Gluten, especially wheat gluten, is the basis for imitation meats resembling chicken, duck (mock duck), fish, pork and beef. 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”, but 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 labeling of other products is voluntary.[13]

Animal feed

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 celiac disease.[15][16] Celiac disease constitutes 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.[18]

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

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