Gluten

right|thumb|upright=1.30|Examples of sources of gluten (clockwise from top): wheat as flour, spelt, barley, and rye as rolled flakes.

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 (common wheat, durum, spelt, khorasan, emmer, and einkorn), 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. These properties, and its relatively low cost, make gluten valuable to both food and non-food industries. 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". 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.

thumb|left|[[Cross section (geometry)|Cross-section of a baguette, showing a strong gluten network.]]

The formation of gluten affects the texture of the baked goods.

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 (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. An increased moisture content in the dough enhances gluten development,

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. 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

thumb|alt=Photo of vegetarian "mock duck" made of wheat gluten in a brine with seasonings.|Gluten is often used in [[Meat alternative|imitation meats (such as this mock duck) to provide supplemental protein in vegetarian diets.]]

Gluten, especially wheat gluten (seitan), 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. 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.

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 (CD), non-celiac gluten sensitivity (NCGS), wheat allergy, gluten ataxia and dermatitis herpetiformis (DH).

Pathophysiological research

The gluten peptides are responsible for triggering gluten-related disorders. Among the gluten peptides, gliadin has been studied extensively.

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 addition, oat products may be cross-contaminated with the other gluten-containing cereals. Some suggested explanations for this increase include the following: the growing westernization of diets, the progressive replacement of rice by wheat in many countries in Asia, the Middle East, and North Africa, 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

thumb|Medical animation still showing flattened [[Intestinal villus|intestinal villi in villous atrophy.]]

Celiac disease (CD) 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. 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.) and adults.

Non-celiac gluten sensitivity

Non-celiac gluten sensitivity (NCGS) is described as a condition of multiple symptoms that improves when switching to a gluten-free diet, after celiac disease and wheat allergy are excluded. Recognized since 2010, it is included among gluten-related disorders. with a prevalence estimated to be 6-10%. NCGS is becoming a more common diagnosis, but its true prevalence is difficult to determine because many people self-diagnose and start a gluten-free diet, without having previously tested for celiac disease or having the dietary prescription from a physician. People with NCGS and gastrointestinal symptoms remain habitually in a "no man's land", without being recognized by the specialists and lacking the adequate medical care and treatment. Most of these people have a long history of health complaints and unsuccessful consultations with numerous physicians, trying to get a diagnosis of celiac disease, but they are only labeled as irritable bowel syndrome.

People with NCGS may develop gastrointestinal symptoms, which resemble those of irritable bowel syndrome or wheat allergy, The results of a 2017 study suggest that NCGS may be a chronic disorder, as is the case with celiac disease.

Wheat allergy

People can also experience adverse effects of wheat as result of a wheat allergy. Wheat allergy and celiac disease are different disorders. Gastrointestinal symptoms of wheat allergy are similar to those of celiac disease and non-celiac gluten sensitivity, but there is a different interval between exposure to wheat and onset of symptoms. An allergic reaction to wheat has a fast onset (from minutes to hours) after the consumption of food containing wheat and could include anaphylaxis. With gluten ataxia, damage takes place in the cerebellum, the balance center of the brain that controls coordination and complex movements like walking, speaking and swallowing, with loss of Purkinje cells. People with gluten ataxia usually present gait abnormality or incoordination and tremor of the upper limbs. Gaze-evoked nystagmus and other ocular signs of cerebellar dysfunction are common. Myoclonus, palatal tremor, and opsoclonus-myoclonus may also appear.

Gluten ataxia accounts for 40% of cases diagnosed as idiopathic ataxia and 15% of all ataxias. Less than 10% of people with gluten ataxia present any gastrointestinal symptom, yet about 40% have intestinal damage. These include peripheral neuropathy, epilepsy, headache, encephalopathy, vascular dementia, and various

movement disorders (restless legs syndrome, chorea, parkinsonism, Tourette syndrome, palatal tremor, myoclonus, dystonia, opsoclonus myoclonus syndrome, paroxysms, dyskinesia, myorhythmia, myokymia).

The diagnosis of underlying gluten sensitivity is complicated and delayed when there are no digestive symptoms. People who do experience gastrointestinal problems are more likely to receive a correct diagnosis and treatment. A strict gluten-free diet is the first-line treatment, which should be started as soon as possible. It is effective in most of these disorders. When dementia has progressed to an advanced degree, the diet has no beneficial effect. Cortical myoclonus appears to be treatment-resistant on both gluten-free diet and immunosuppression. The term "gluten-free" is generally used to indicate a supposed harmless level of gluten rather than a complete absence.

For persons with celiac disease, consumption of more than 10 mg of gluten per day will cause intestinal architecture changes in the majority of celiacs. Based on this study by Catassi et al, many jurisdictions opt to use 20 parts per million as the regulatory threshold for a gluten-free claim, which enables someone to consume >500 g of food at <20 parts per million. Those with celiac disease must avoid traces of gluten even if they do not experience overt acute symptoms from cross-contact. The ED05 for a discrete exposure in a wheat allergic person is 6.1 mg. Because those with wheat allergies may react to proteins other than gluten in wheat, some gluten-free products (e.g. gluten-free wheat starch) may be inappropriate for them.

There is no established threshold for those with NCGS, but some double blind feeding studies suggest no effect when 10 grams of gluten is consumed per day. Whether symptoms are alleviated due to gluten elimination or some other component in gluten grains is scientifically debated.

Australia and New Zealand

Gluten is defined to include wheat, barley, rye, and oats. If gluten is present as an intentional ingredient in a packaged product, these ingredients must be declared in the ingredient list. Beers labelled gluten-free cannot contain barley ingredients irrespective of the level of quantitative gluten. A "low gluten" claim may be used where the product has less than 200 parts per million gluten.

Canada

Labels for packaged products sold in Canada must clearly identify the presence of gluten (wheat, barley, rye, oats, triticale) if these are present as an intentional ingredient in the food product. Foods labelled gluten-free must be free of gluten ingredients (wheat, barley, rye) and be below 20 parts per million gluten from cross-contact. Misleading claims such as "low gluten" or "reduced gluten" are not permitted.

In 2015, a market authorization was initiated by the Minister of Health, permitting the inclusion of uncontaminated oats (<20 parts per million) in gluten-free labelled items. Similar to the US law, foods with intentional gluten ingredients such as enzyme treated barley beer may not be labelled gluten-free even if they test below 20 parts per million gluten.

European Union and United Kingdom

All foods containing gluten as an intentional ingredient must be labelled accordingly as gluten is defined as one of the 14 recognised EU allergens. Foods, including non-packaged foods bearing a gluten-free claim must be below 20 parts per million, irrespective of ingredients. Foods may also be labelled "very low gluten," which is defined as 100 parts per million of gluten or less. This aspect of the regulation is controversial as the ELISA immunoassay cannot reliably detect fragments of gluten proteins, whereas there is evidence that those with celiac disease can react to these protein fragments. Other jurisdictions such as Canada and the United States have dealt with this controversy by prohibiting gluten protein fragment ingredients.

It is not permissible to label food as "gluten-free" when all similar food is naturally gluten-free, such as in the case of milk.

United States

In the United States, gluten grains other than wheat do not need to be declared when they are intentional ingredients in a food product. Packaged products bearing a claim of "gluten-free", "no gluten," "free of gluten," or "without gluten," cannot have gluten protein ingredients (wheat, barley, rye) and must be below 20 parts per million from cross-contact. Additionally, fermented or hydrolyzed foods (e.g. soy sauce, beer) cannot be labelled gluten-free unless the raw ingredients comply with the gluten-free label rule.