Gluten

Sources of gluten. Clockwise from top: High-gluten wheat flour, European spelt, barley, rolled rye flakes.

Gluten (from Latin gluten, "glue") is a protein composite found in wheat and related grains, including barley and rye. 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.^[1]

Gluten is the composite of the storage proteins gliadin and a glutenin, and 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.

Extraction

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/low temperature water, and the dispersed starch will be sedimented and dried.^[2] If a saline solution is used instead of water, a purer protein is obtained, with certain harmless impurities going into the 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.^[3] 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.^[4]

Uses

Wheat, a prime source of gluten

Bread products

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.^[5] 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.^[6]

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.^[7][8] 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.^[9]

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,^[9] 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.^[10][11]

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.^[12] 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.^[13] Generally, higher gluten levels are associated with higher amounts of overall protein.^[14]

Imitation meats

Gluten is often used in imitation meats (such as this mock "duck") to provide supplemental protein and variety in vegetarian diets.

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 flavor) and becomes firm to the bite.^[15][16]

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.^[17][18] Foods of this kind raise a problem, because the hidden gluten constitutes a hazard for people with celiac disease.

Animal feed

The protein content of some pet foods may also be enhanced by adding gluten.^[19]

Adverse reactions

In individuals with coeliac disease (American English: celiac), consumption of gluten causes adverse health issues ranging from abdominal bloating, gas, diarrhea and vomiting to migraine headaches and joint pain. Coeliac disease is an autoimmune disorder that affects the digestive process of the small intestine. 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.^[20][21][22] It probably occurs with comparable frequency among all wheat-eating populations in the world.^[23] Coeliac disease has no cure but is manageable with a gluten-free diet.

Non-coeliac gluten sensitivity (sometimes known as gluten intolerance) is a condition thought to arise as a result of an immunological response to gluten that differs in nature to the immune response characteristic of coeliac disease. However, there is no current scientific consensus that this is a genuine pathological condition and the mechanism by which this could occur is unknown. Frequently, symptoms could arise in individuals as a result of undiagnosed coeliac disease or due to a reaction to other components of wheat, such as short-chain, fermentable carbohydrates called FODMAPs.^[24][25]

People can also experience adverse effects of wheat as result of a wheat allergy. As with most allergies, a wheat allergy causes the immune system to abnormally respond to a component of wheat that it treats as a threatening foreign body. This immune response is often time-limited and does not cause lasting harm to body tissues.^[26] Wheat allergy and coeliac disease are different disorders.^[27]

Labelling

International standards

The Codex Alimentarius international standards for food labelling has a standard relating to the labelling of products as "gluten-free". It only applies to foods that would normally contain gluten.^[28]

Brazil

By law in Brazil, all food products must display labels clearly indicating whether or not they contain gluten.^[29]

Canada

Only one in 133 Canadians experiences adverse symptoms from gluten in celiac disease.^[30] Labels for all food products sold in Canada must clearly identify the presence of gluten if it is present at a level greater than 20 parts per million.^[31]

United Kingdom

In the United Kingdom, only cereals must be labelled; labelling of other products is voluntary.^[32]

United States

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"). In August 2013, FDA issued a final rule, effective August 2014, 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 parts per million."^[33]

References

Bibliography

• 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. 

Barley History Domestication Neolithic Revolution Triticeae Types of barley Genus: Hordeum Cultivars: Bere Agronomy Barley diseases Trade Australian Barley Board Canadian Wheat Board Corn exchange Production by country Wheat pools in Canada Parts of the plant Bran Germ Husk Kernel Gluten Straw Basic preparations Milling: Flour (types) Groats Middlings Parboiling As an ingredient Barley bread Barley honey Beer Caffè d'orzo Irish whiskey Japanese whisky Malta Roasted barley tea Scotch whisky Talbina Barley water see also: Category:Barley-based beverages Associated human diseases Gluten-related disorders Coeliac disease Non-celiac gluten sensitivity Related concepts Bread riot Cattle feeding Plant breeding Refined grains Staple food Whole grain Further information

Wheat History Domestication Shattering Neolithic Revolution Tell Abu Hureyra Tell Aswad Triticeae Types Common Durum Einkorn Emmer Khorasan Norin 10 Red Fife Spelt Winter wheat Agronomy Wheat diseases (list) Wheat mildew Trade Australian Wheat Board Canadian Wheat Board Corn exchange International Wheat Council Peak wheat Production statistics Protein premium Wheat pools in Canada Parts of the plant and their uses Stalk Straw Seed Bran Germ Chaff (husk) Endosperm Gluten Basic preparations of the kernel None Wheat berry Milling Farina Flour (types) Middlings Semolina Parboiling Bulgur As an ingredient Bread Couscous Cracker Flatbread Pasta Rava dosa Upma Wheat beer Wheat germ oil Wheat gluten Associated human diseases Anaphylaxis Gluten-related disorders (including coeliac disease, non-celiac gluten sensitivity and wheat allergy) Related concepts Bread riot Plant breeding Refined grains Staple food Wheatpaste Whole grain Further information