The quest for celiac-safe wheat

Gluten proteins from wheat have the unique property to interact with each other and form a network in dough preparation. In this gluten network gas bubbles can be retained that are produced by yeast, which is added during dough preparation. The result is a voluminous, viscoelastic dough for bread making. Besides these network forming properties, gluten proteins contain remarkably high amounts of the amino acids proline and glutamine. Therefore, these proteins can not be degraded completely in the human gastrointestinal tract and so called epitopes are generated in the small intestine after ingestion of gluten containing foods such as bread and cookies. Intolerance to gluten proteins can cause inflammation of the small intestine, which leads to villous atrophy (flatten mucosa) and malabsorption. This intolerance to gluten proteins is also called celiac disease. The with celiac disease occurring inflammation can lead to many symptoms such as malnutrition, weight loss, stomach pain, diarrhea, dermatitis and in the worst case lymphoma. In children, celiac disease can cause growth retardation. Gluten proteins from rye and barley, because of their similarity to gluten proteins from wheat and high proline and glutamine content, can also cause celiac disease. Celiac disease patients therefore have to avoid life-long all food products containing wheat, rye, and barley (gluten-free diet). Not only gluten protein intake but also genetic susceptibility is necessary to develop celiac disease. Therefore, relatives of celiac disease patients have a highly increased risk to develop celiac disease. About 0.52% of the Western population suffers from celiac disease of which 7097% is undiagnosed, and the prevalence of celiac disease is still increasing. The reason for this may be the consumption of many bread, cookie and pasta products, but also because wheat constituents, such as gluten and starch, are increasingly used as food additive in soups, sauces, sausage, candy, ice-cream, and even in medicines.
Because bread wheat originated thousands of years ago by fusion of three different grass species, many different gluten proteins exist. Pasta wheat originated from two of the three grass species and lacks the species that contains most of the celiac disease epitopes. Not all gluten proteins can be removed because baking properties might be lost. For analysis of the presence of celiac disease epitopes, it is important that all gluten proteins are extracted from the wheat kernels. Therefore, an extraction protocol was developed to extract as many gluten proteins as possible, which allows analysis of many samples at the same time. Because thousands of different wheats exist that have never been tested for celiac disease epitopes, this extraction and detection method was applied to analyze whether modern wheats, which are used by breeders, exist with lower amounts of celiac disease epitopes. These modern wheats were subsequently compared to old wheats collected from all over the world. From these analyses it seemed that there was an increase in celiac disease epitopes in modern wheats. This might be the reason for the increase of prevalence of celiac disease. For future breeding of bread wheat it is important to select and breed not only for high yield, disease/pest resistance, and baking quality, but also for the (reduced) presence of relevant celiac disease epitopes. In older bread and pasta wheats, we observed that fewer celiac disease epitopes are present. Knowing this, a more celiac-safe bread wheat could be developed by performing crossings with a selection of wheats. In the analysis of wheat lines that miss specifically genetic parts of one of the three grass species from which bread wheat evolved, it appeared that if the part is removed that encodes celiac disease epitopes to which most patients respond, the dough properties improved compared to the control dough. By addition of similar proteins from oat (avenins), the dough properties improved even more. These gluten proteins from oat are tolerated by most celiac disease patients. The results show that it is feasible to develop wheat that contains less celiac disease epitopes without decreasing dough properties.
Celiac disease patients, however, respond differently to different celiac disease epitopes which complicates the development of wheat that is suitable for all celiac disease patients. The research performed in this thesis shows that selection of wheat for the presence of celiac disease epitopes is extremely relevant because it can reduce the number of celiac disease patients in the future. At the same time, we demonstrate that celiac-safe wheat can still maintain good baking properties. Diagnosed celiac disease patients will benefit as well from celiac-safe wheat because exposure to ‘hidden’ gluten proteins will decrease.