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, and 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 and rice, 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 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.
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 ; pastry flours have a lower gluten content. Kneading promotes the formation of gluten strands and cross-links, creating baked products that are chewier. 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. 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, is often the basis for imitation meats resembling beef, chicken, duck, fish and pork. When cooked in broth, gluten absorbs some of the surrounding liquid 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
"Gluten-related disorders" is the umbrella term for all diseases triggered by gluten, which include celiac disease, non-celiac gluten sensitivity, wheat allergy, gluten ataxia and dermatitis herpetiformis.Pathophysiological research
The gluten peptides are responsible for triggering gluten-related disorders. In people who have celiac disease, the peptides trigger an immune response that causes injury of the intestines, ranging from inflammation to partial or total destruction of the intestinal villi. To study mechanisms of this damage, laboratory experiments are done in vitro and in vivo. Among the gluten peptides, gliadin has been studied extensively.''In vitro'' and ''in vivo'' studies
In the context of celiac disease, gliadin peptides are classified in basic and clinical research as immunogenic, depending on their mechanism of action:- The peptides are those capable of directly affecting cells and intestinal preparations in vitro, producing cellular damage in vivo and eliciting the innate immune response. In vitro, the peptides promote cell apoptosis and inhibit the synthesis of nucleic acids and proteins, reducing the viability of cells. Experiments in vivo with normal mice showed that they cause an increase in cell death and the production of interferon type I. In vitro, gluten alters cellular morphology and motility, cytoskeleton organization, oxidative balance, and tight junctions.
- The immunogenic peptides are those able to activate T cells in vitro.
The effect of oat peptides in celiac people depends on the oat cultivar consumed because of prolamin genes, protein amino acid sequences, and the immunotoxicity of prolamins which vary among oat varieties. In addition, oat products may be cross-contaminated with the other gluten-containing cereals.
Incidence
, gluten-related disorders were increasing in frequency in different geographic areas. Some suggested explanations for this increase include the following: the growing westernization of diets, the increasing use of wheat-based foods included in the Mediterranean diet, the progressive replacement of rice by wheat in many countries in Asia, the Middle East, and North Africa, the higher content of gluten in bread and bakery products due to the reduction of dough fermentation time, and the development in recent years of new types of wheat with a higher amount of cytotoxic gluten peptides. However, a 2020 study that grew and analyzed 60 wheat cultivars from between 1891 and 2010 found no changes in albumin/globulin and gluten contents over time. "Overall, the harvest year had a more significant effect on protein composition than the cultivar. At the protein level, we found no evidence to support an increased immunostimulatory potential of modern winter wheat."Celiac disease
is a chronic, multiple-organ autoimmune disorder primarily affecting the small intestine caused by the ingestion of wheat, barley, rye, oats, and derivatives, that appears in genetically predisposed people of all ages. CD is not only a gastrointestinal disease, because it may involve several organs and cause an extensive variety of non-gastrointestinal symptoms, and most importantly, it may be apparently asymptomatic. Many asymptomatic people become accustomed to living with a chronic bad health status as if it were normal, but they are able to recognize that they actually had symptoms related to celiac disease after starting a gluten-free diet and improvement occurs. Added difficulties for diagnosis are the fact that serological markers are not always present and many people may have minor mucosal lesions, without atrophy of the intestinal villi.CD affects approximately 1–2% of the general population, but most cases remain unrecognized, undiagnosed and untreated, and at risk for serious long-term health complications. People may suffer severe disease symptoms and be subjected to extensive investigations for many years, before a proper diagnosis is achieved. Untreated CD may cause malabsorption, reduced quality of life, iron deficiency, osteoporosis, an increased risk of intestinal lymphomas, and greater mortality. CD is associated with some other autoimmune diseases, such as diabetes mellitus type 1, thyroiditis, gluten ataxia, psoriasis, vitiligo, autoimmune hepatitis, dermatitis herpetiformis, primary sclerosing cholangitis, and more.
CD with "classic symptoms", which include gastrointestinal manifestations such as chronic diarrhea and abdominal distention, malabsorption, loss of appetite, and impaired growth, is currently the least common presentation form of the disease and affects predominantly small children generally younger than two years of age.
CD with "non-classic symptoms" is the most common clinical type and occurs in older children, adolescents, and adults. It is characterized by milder or even absent gastrointestinal symptoms and a wide spectrum of non-intestinal manifestations that can involve any organ of the body, and very frequently may be completely asymptomatic both in children and adults.
Asymptomatic CD is present in the majority of affected patients and is characterized by the absence of classical gluten-intolerance signs, such as diarrhea, bloating, and abdominal pain. Nevertheless, these individuals very often develop diseases that can be related to gluten intake. Gluten can be degraded into several morphine-like substances, named gluten exorphins. These compounds have proven opioid effects and could mask the deleterious effects of gluten protein on gastrointestinal lining and function.