In people with coeliac disease, those proteins cause an inflammatory response which leads to intestinal damage. Even traces of gluten can cause discomfort. People with coeliac disease or non-coeliac gluten sensitivity, must avoid food made with any of these grains and have to pay attention to cross-contamination.
When it comes to wheat the proteins are named as gliadins and glutenins, in barley it is hordein and in rye secalins.
It is the group called prolamins, the alcohol-soluble protein fractions of these grains, which are toxic to people with coeliac disease. These are:
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Wheat (gliadin)
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Barley (hordein)
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Rye (secalin)
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Botanically related species, e.g. as spelt, green spelt, kamut, emmer and einkorn
Nutritionally those proteins aren’t essential to cover the protein intake, however they do have very unique properties which make the doughs rise and confer baked goods the characteristic “doughy” and crunchy texture we all know well.