Establishing the Flour Reference Proteome for Five Wheat Species

The protein composition of the five types of wheat—einkorn, emmer, spelt, durum, and common wheat—and their varieties differ widely. This is the result of large-scale research conducted by the University of Hohenheim in Stuttgart and the University Medical Center Mainz.

In 150 flour samples, the researchers discovered a total of 2,896 distinct proteins. Apart from the cultivation site, the variety also has an important role. This knowledge could be put to good use: Proteins, whose occurrence is mostly determined by variety, may be influenced by targeted breeding. This could result in increased baking quality, higher yields, and tolerance.

Wheat is a vital and relatively healthy staple food for both human and animal nutrition. Along with dietary fiber, minerals, and vitamins, it offers about 20% of the daily needed amount of protein when ingested with 100 to 150 g of wheat flour.

At the same time, wheat flour’s proteins are essential to its baking quality. That is why understanding the proteome, or the entirety of all proteins generated in cereals, is important—both for selecting the proper variety and for future-focused breeding studies.

Even so, not all wheat is the same. Despite their close botanical connection, the constituents of bread (Triticum aestivum ssp. aestivum) and durum wheat (Triticum turgidum ssp. durum) vary, as do those of spelt (Triticum aest ivum ssp. spelta), emmer (Triticum turgidum ssp. dicoccum), and einkorn (Triticum monococcum ssp. monococcum). However, there has been no meaningful data to permit for a direct comparison so far.

Milestone for Future Protein Research

Against this backdrop, scientists from the Universities of Hohenheim and Mainz examined all of the proteins found in whole grain flour made from these five varieties of wheat. They looked at ten different species. These were grown in three distinct locations to represent the influence of environmental conditions.

The researchers identified 2,896 distinct proteins in the 150 flour samples, with over 2,500 in each species. Approximately half of all proteins differed between species during the process.

To our knowledge, this is one of the most comprehensive proteomic studies in cereals to date. It sets a milestone for much more targeted protein research in wheat in the future.”

Dr Friedrich Longin, Professor, State Plant Breeding Institute, University of Hohenheim

Protein Composition Depends on Location and Variety

For their evaluations, the scientists compared the proteins or subsections of them seen in various databases whenever possible. However, a major portion of them had not yet been thoroughly researched.

“Many of the known proteins play a role in product quality, such as in the formation of cereal starch or in stress regulation of plants, but also in allergic reactions in humans,” Prof. Longin notes.

It is true that a considerable proportion of proteins is formed as a result of environmental influences. However, several proteins are more prevalent in some kinds. The researchers discovered a total of 2,540 proteins in einkorn, 1,940 of which were generated in at least one cultivar at all three places.

Since genetic factors are primarily responsible for this, we have a good starting point for selecting and breeding better wheat varieties.”

Dr Friedrich Longin, Professor, State Plant Breeding Institute, University of Hohenheim

The researchers created a list of proteins that might be impacted by variety selection.

Significantly Fewer Allergenic Proteins in Einkorn

“Up to ten percent of people who eat products made with wheat flour complain of discomfort afterwards. The proteins found in wheat cause them to develop what is known as non-celiac wheat sensitivity (NCWS), which has not yet been well-defined. Another result is celiac disease—an inflammatory disease of the small intestine caused by gluten proteins in wheat, and some people develop a classic (immediate type) wheat allergy. In addition, there is also a much more frequent wheat allergy of the delayed type, especially in patients diagnosed with irritable bowel syndrome.”

Dr Dr Detlef Schuppan, Professor, University Medical Center, Johannes Gutenberg University Mainz.

The number of potentially allergenic proteins in the wheat species tested varies greatly. The total allergen frequency of common wheat and spelt is roughly the same. In comparison, durum wheat and emmer reduce them by around two times, and einkorn reduces them by 5.4 times. The experts have yet to come up with an explanation for this phenomenon.

The quantity of ATIs (alpha-amylase/trypsin inhibitors) in particular varies greatly.

“They are suspected of being responsible for inflammatory reactions. Compared to the other wheat species, einkorn has a significantly lower amount of ATIs,” adds Prof. Dr. Stefan Tenzer from the Institute of Immunology at the University Medical Center Mainz.

Clinical Studies Urgently Needed

The researchers point out that they anticipated the allergenic ability purely by cross-referencing with databases that list potential allergenic proteins. Targeted research would need to demonstrate whether these findings are also clinically relevant.

“In light of our results, a clinical trial with einkorn compared to modern wheat would be particularly interesting,” said Prof. Schuppan.

The detailed mapping of these proteins, for example, can aid in the designing of representative test diets.

“To find products that are better tolerated, especially for people with wheat-related diseases, we also need to investigate what influence different processes in flour and bread production, such as a long sourdough fermentation, have on allergens,” added Prof. Longin.

Outlook: Einkorn as a Sustainable Crop for Marginal Lands

In addition to the lesser amount of potential allergens, einkorn has more protein and considerably higher amounts of secondary plant compounds, vitamins, and minerals compared to common wheat. Einkorn is also intriguing from an agricultural point of view:

“It has almost complete resistance to fungi. Moreover, it can be sown either before or after winter, which is not the case with other cereals,” says Prof. Dr Longin.

Under favorable soil conditions, however, einkorn yields are substantially lower than typical wheat yields.

“However, in marginal lands, such as sandy soils, higher elevations in mountainous regions, or where the use of nitrogen fertilizer is not possible, good results are obtained with einkorn, while the productivity of common wheat decreases,” concludes Prof. Longin, elucidating a possible application.