Gluten digestion: breakdown and development of inflammation

Gluten is composed of two main fractions, which are distinguished according to their solubility in alcohol and water: soluble prolamines and insoluble glutenins. These fractions have different names depending on the type of grain – in wheat, they are called gliadins and glutenins. Both consist of complex mixtures of different protein components. They are characterised by their high content of the amino acids glutamine and proline, while essential amino acids are only present in small amounts. Glutamine- and proline-rich sequences are considered difficult to digest and play a central role in coeliac disease. Due to the different gene variants, each cultivated wheat variety can be identified by the composition of its protein reserves – a kind of individual fingerprint.

The digestion of protein, and therefore also gluten, begins in the stomach with the enzyme pepsin and continues in the small intestine with other enzymes from the pancreas and the intestinal mucosa. The high proportion of glutamine and proline in certain sections of gluten makes it particularly difficult to digest. As a result, certain peptide fragments – such as the well-known 33-mer from α-gliadin – remain in the intestine for longer and can activate the immune system in people with coeliac disease. In people with coeliac disease, the consumption of gluten triggers a misguided immune response involving both B cells and T cells. It is crucial that only certain gluten peptides – especially those that have been deamidated by the enzyme tissue transglutaminase (tTG) – are strong enough to trigger this immune response.