GLUTEN

Wheat seed, sectioned to reveal endosperm and embryo

Wheat - a prime source of gluten

'Gluten' is a mixture of the proteins ''gliadin'' and ''glutenin''. These exist, conjoined with starch, in the endosperms of some grass-related grains, notably wheat, rye, and barley. Gliadin and glutenin comprise about 80% of the protein contained in wheat seed. Being insoluble in water, they can be purified by washing away the associated starch. Gluten is a globally important source of nutritional protein, both in foods prepared directly from it and as an additive to foods otherwise low in protein.
As with wheat, the seeds of most flowering plants have endosperms with stored protein to nourish embryonic plants during germination, but true gluten, with gliadin and glutenin, is limited to certain members of the grass family. The stored proteins of corn and rice are sometimes called glutens, but their proteins differ importantly from wheat gluten by lacking glutenin. The glutenin in wheat flour gives kneaded dough its elasticity, allowing leavening and contributing chewiness to baked products like bagels.
Although wheat supplies much of the world's dietary protein, a small percentage of the populace, including those with coeliac disease, is gluten-intolerant and cannot consume it safely. ^[1]

Extraction

Legend attributes the discovery of gluten to Buddhist monks in 7th century China who sought meat-like ingredients for use in their vegetarian diet. With easily available wheat flour and water they made a dough which they submerged in cold water and kneaded. The water dissolved the starchy components of the dough and left behind an insoluble, gummy mass, 70% to 80% of which was gluten.^[2]
Gluten is still extracted from flour by washing out the starch by means not fundamentally different from the ancient way, which exploited the fact that starch is water-soluble while gluten is not. 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, so cold water is the favored solvent. To effect the separation, a slurry of wheat flour is stirred vigorously by machinery until the starch dissolves and the gluten consolidates into a mass, which is collected by centrifugation, then carried, by complex machinery,^[3] through several stages combined into a continuous process: Approximately 65% of the water in the wet gluten is removed by means of a screw press, and the residue is sprayed through an atomizing nozzle into a drying chamber, where it remains at an elevated temperature only long enough to evaporate the water without denaturing the gluten. This yields a flour-like powder with a 7% moisture content, which is quickly air-cooled and pneumatically transported to a receiving vessel. In the final step, the collected gluten is sifted and milled to make the product uniform. ^[4]

Uses

When cooked in broth, gluten absorbs some the surrounding liquid, including the taste, and becomes firm to the bite, so it is often used in vegetarian, vegan and Buddhist cuisines as a meat substitute. In China, as ''miàn jīn'', it is the basis for imitation meats resembling chicken, duck, fish, pork and beef. The Japanese variant, called ''seitan'' is used in the same way.
When dough made with wheat flour is kneaded, the gluten molecules cross-link to form a sub-microscopic network. If such dough is leavened with yeast, sugar fermentation produces bubbles of carbon dioxide and the bubbles are trapped by the gluten network, causing the dough to swell or ''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 by hydration.^[5]
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 because that fraction contains the preponderance of the sulfur atoms responsible for the cross-linking in the network.^[6]^[7]
More development leads to chewier products like pizza and bagels, while less development yields tender baked goods such as pie crust. Several other factors affect the development of gluten in baked goods:

★ The amount of gluten in the flour. For examples, bread flour has high gluten content, while cake flour is low in gluten.

★ Fat inhibits the formation of long gluten strands, so increased shortening yields a more tender product.

★ Kneading develops the gluten strands, so a baked product is chewier in proportion to how much the dough is worked.

★ Water is essential to gluten development, so more of it is used in doughs when a chewier texture is desired.^[8]
:As a practical application of these rules, pie crust, which should be very tender, is made with low-gluten flour, much shortening, and little liquid, then mixed only enough to combine the ingredients.
Gluten can be dried and milled into a flour or powder, which, added to ordinary flour dough, makes for higher rising and increases the bread's structural stability and chewiness.^[9]. Since such doughs must be worked vigorously if they are to rise to their full capacity, a bread machine or food processor may be required for their kneading.^[10]
Gluten is used as a protein supplement, especially in low-carbohydrate baked goods where it replaces flour. It is also added to many pet foods to increase their protein content.^[11]

Occurrence

Gluten is found in wheat and closely related cereals like rye and barley. Wheat grown in countries with cold growing seasons, e.g. Canada, tends to have a higher gluten content than wheat grown in countries with mild climates. Wheat flour with a high gluten content is called "strong" or "hard" flour, and is used for breads, whereas flour with a lower gluten content is called "soft" flour, and is used for cakes.
Some varieties of wheat, including kamut and spelt, naturally have low contents of gluten.^[12] The gluten in spelt is more fragile than that found in ordinary wheat, so dough made with it collapses when overkneaded.^[13] Many gluten sensitive people can tolerate these varieties, but those with coeliac disease should avoid all food containing wheat derivatives.
Rice (even the so-called glutinous rice) contains no gluten, nor do wild rice, maize (corn), millet, sorghum, buckwheat, quinoa, or amaranth. (the latter three being broad-leaf grains, and not true cereals). Oats and teff have no native gluten, but are sometimes contaminated by milling with equipment also used for wheat or other cereals. Oats lack many of the prolamines found in wheat but do contain avenin.^[14] Avenin is toxic to the intestinal submucosa of some individuals with coeliac disease.^[15]
Non-cereals, including legumes such as soybeans, seeds such as sunflower seeds, and pseudocereals such as quinoa, contain no gluten. Corn storage protein (often called "corn gluten") is devoid of gluten, despite its common name. Corn does contain prolamines, like wheat, so it may be toxic for some with celiac disease.^[16]

Adverse reactions

Between 0.5 and 1.0 percent of the United States populace is sensitive to gluten."http://digestive.niddk.nih.gov/ddiseases/pubs/celiac/index.htm"
National Digestive Disease Clearing House, NIH (2004} ''Celiac Disease'' Accessed 28-Aug-2006
^[17] Celiac disease, also called gluten sensitive enteropathy (GSE), is the predominant disorder caused by gluten sensitivity. GSE is an abnormal immune reaction to digestive breakdown products of gliadin. Incurable, it damages the lining of the small intestine, which results in chronic malnutrition. Treatment requires a lifelong gluten-free diet and avoiding exposure to air-borne gluten-containing particles such as wheat flour. Gluten allergies and gluten-sensitive idiopathic neuropathies are two other adverse reactions to gluten.^[18]
Patients with conditions associated with GSE also benefit from a gluten-free diet and avoiding gluten inhalation. An example of gluten-related skin sensitivity is dermatitis herpetiformis, an intensely itchy skin eruption, which is nearly always accompanied by coeliac disease. This dermatitis usually develops in young adults, preferentially in males; people of North European ethnicity are especially susceptible.^[19]

References

1. Hill, I. D., Horvath, K., and Fasano, A., ''Epidemiology of celiac disease.'' 1: Am J Gastroenterol. 1995 Jan;90(1):163-4
2. Hail, Seitan Caitanya Bhagavat Das
3. Starch Technology & Industrial Biotechnology
4. http://www.barr-rosin.com/applications/wheat.asp ''Wheat'', GEA Barr-Rosin, Accessed 2007-09-04
5. 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 analyses.
6. Role of gluten and its components in determining durum semolina dough viscoelastic properties, , N. M., Edwards, Cereal chemistry, 2003
7. Modification of the Low Molecular Weight (LMW) Glutenin Composition of Transgenic Durum Wheat: Effects on Glutenin Polymer Size and Gluten Functionality, , Paola, Tosi, Molecular Breeding, 2005
8. Baking Technology, Bread
9. Amendola, J., Rees, N., & Lundberg, D. E. (2002). ''Understanding Baking''
10. Echkardt, LW & Butts, DC. (1997). ''Rustic European Breads from your Bread Machine''
11. Pet Foods
12. Progress in New Crops, , G.F., Stallknecht, ASHS Press, 1996,
13. The Spelt Cookbook, , Helga, Hughes, Avery, 1995,
14. On the Use of Oats in the Gluten-Free Diet, , Leon H., Rottmann, Lifeline, 1996
15. The Scoop on Oats
16. Corn Gluten - Is it Safe for a People with Celiac Disease Who are on a Gluten-Free Diet?
17. Celiac disease
18. Gluten Sensitive Enteropathy David A. Nelsen
19. Dermatitis Herpetiformis

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