What is gluten?
Gluten is a term for insoluble proteins, or proteins that won’t dissolve in water, found in wheat, barley and rye grains. The term literally means “glue” in Latin, referring to how they bind together to make the characteristic chewiness and fluffiness in gluten-containing bread and bakery items. They are the most abundant proteins in wheat grains, and are used to store nitrogen and amino acids to fuel growth of the new plant that sprouts from the grain seed.
Is Wheat Gluten Different from Gluten?
Wheat gluten is composed of two types of proteins, gliadins and glutenins, while barley contains hordeins and rye grains contain secalins, proteins similar to gliadins which are also considered gluten due to their similar structures and effects in the body. Other grains have the same types of proteins, called prolamins, with oats containing avenins, corn containing zeins and rice containing oryszins. However, these grains contain lower amounts of prolamins, with different structures that don’t trigger immune reactions as commonly as gluten and so aren’t classified as gluten proteins.
What is Gluten Made of?
Proteins are made of long chains of amino acids, chemical compounds with carbon, hydrogen and nitrogen atoms and different side chains which could include other elements like sulfur, depending on the type of amino acid. They link to each other through a carbon of one amino acid bonding to a nitrogen of another, forming a backbone with side chains sticking out. The sequence of types of amino acids determines the type of protein and its shape, because the long chains fold and and connect to themselves through bonds such as disulfide bonds between sulfur atoms on side chains of cysteine amino acids in the chain. Gluten proteins are characterized by short repeating patterns amino acids and high contents of proline and glutamine.
What Does Gluten Look Like?
When wheat flour is combined with water, gluten proteins link together by forming disulfide and hydrogen bonds between their chains. Kneading allows the proteins to line up and form more bonds, forming a mesh structure. Gluten strength is a term used in breadmaking and baking that describes how strong the structure is. The stronger the gluten strength, the more stretchy the dough and the more gas it will hold to make it airy and light. Gluten proteins are generally not soluble in water, so washing away the water-soluble components of wheat flour will leave a sticky mass that forms a yellow-gray powder when dried (Blakemore & Jennet, 2018).
What are the Types of Gluten?
The term gliadin defines a group of gluten proteins that can be separated from other gluten proteins in 70% ethanol. Glutenin proteins are insoluble in alcohol. There are many different types of gliadin with different sequences of amino acids, classified into four general categories, alpha, beta, gamma and omega gliadins, based on their size and electrical charge. Glutenin is categorized based on its molecular weight, high, medium or low (Urade et al., 2018).
Deamidated Gluten
Deamidated gliadin has been made more negatively charged by an enzyme found in the intestinal tract and other parts of the body called tissue transglutaminase (tTG). It converts the glutamine amino acids in gliadin to glutamic acid, making it more reactive with the immune system. In doing so, tTG can link up with gliadin particles, forming a tTG-gliadin complex that also causes an immune reaction. Presence of anti-tTG antibodies, produced by the immune system in response to tTG-gliadin complexes, are a main indicator of celiac disease (Ciccocioppo et al., 2003).
Microbial Transglutaminase
The food industry uses microbial transglutaminase (mTG), which has the same effects as tTG but is made from bacteria, to make gluten more water soluble so it can be used as fillers and additives in food products. In the process, mTG combines gliadin proteins to make huge protein complexes that can trigger an immune response. The combination of tTG and mTG reacts with gliadin in the body and causes immune responses called neo-mTG and neo-tTG antibodies (Lerner & Benzvi, 2021).
Gluteomorphins
Finally, gluteomorphins, also called gluten exorphins, are byproducts of gliadin digestion. They have a structure similar to morphine, and can attach to opioid receptors and cause addiction and immune reactions. This can make gluten extremely addictive for some people (Pruimboom & de Punder, 2015).
References
Blakemore, C. & Jennet, S. (2018). Gluten: The Oxford companion to the body. Retrieved April 13, 2023 from Encyclopedia.com: https://www.encyclopedia.com/medicine/encyclopedias-almanacs-transcripts-and-maps/gluten
Urade, R., Sato, N., & Sugiyama, M. (2018). Gliadins from wheat grain: An overview, from primary structure to nanostructures of aggregates. Biophysical reviews, 10(2), 435–443. https://doi.org/10.1007/s12551-017-0367-2
Ciccocioppo, R., Di Sabatino, A., Ara, C., Biagi, F., Perilli, M., Amicosante, G., Cifone, M. G., & Corazza, G. R. (2003). Gliadin and tissue transglutaminase complexes in normal and coeliac duodenal mucosa. Clinical and experimental immunology, 134(3), 516–524. https://doi.org/10.1111/j.1365-2249.2003.02326.x
Lerner, A., & Benzvi, C. (2021). Microbial transglutaminase is a very frequently used food additive and is a potential inducer of autoimmune/neurodegenerative diseases. Toxics, 9(10), 233. https://doi.org/10.3390/toxics9100233
Pruimboom, L., & de Punder, K. (2015). The opioid effects of gluten exorphins: Asymptomatic celiac disease. Journal of health, population, and nutrition, 33, 24. https://doi.org/10.1186/s41043-015-0032-y
