Making dough

A Kansas State University scientist has solved a problem that has confounded the baking industry for more than 50 years: when you mix flour and water, what chemical reaction causes the elastic bread dough to form?

Katherine A. Tilley, a cereal chemist in the department of grain science and industry, has shown experimentally that within the wheat flour protein called gluten, tyrosine molecules reacting with other tyrosine molecules - either on the same protein chain or across separate protein chains - build up a complex network of strong cross-links. Tyrosine cross-links become the scaffolding of dough.

Two patent applications have been filed by the Kansas State University Research Foundation to cover the tyrosine cross-link discovery. In all, the patent applications make 20 independent claims and nearly 86 dependent claims for the invention ranging from dough, wheat quality and bread-making to its potential usefulness in molecular biology and synthetic peptide chemistry.

Gluten is the protein component of wheat flour. It's what gives bread dough its viscous and elastic properties when mixed and kneaded, and its unique light airy texture when baked, Tilley explained.

Tyrosine is an amino acid or 'building block' of gluten protein structure. Tilley's research establishes the relationship between tyrosine cross-linking and gluten quality. In other words, wheat flour gluten is only as good for baking as its tyrosine cross-linking potential.

Brendan Donnelly, head of K-State's department of grain science and industry, said Tilley's discovery is significant in the field of cereal chemistry and has tremendous implications for the milling and baking industries.

'The baking industry has thought for more than half a century that dough forms because disulphide bonds are breaking and reforming, breaking and reforming, but no scientist had ever actually shown this to be the case,' Donnelly said.

'Being able to measure and monitor tyrosine cross-linking formation will be a tremendous savings to the baking industry because it offers the potential ability to control the uniformity of flour quality.'

Ron Trewyn, K-State vice provost for research and president of the KSU Research Foundation, said the discovery sets the stage for precise quality control throughout the flour milling and bread-baking processes. Eventually, the discovery will have an impact on wheat breeding programs and on the possible future development of improved cereal crops that have flour-making capacity.

'As a result of this new knowledge, we may also see a day when specialty or branded wheat becomes common, that is, wheat created specifically for an intended baked product,' he said.

Tyrosine cross-linking also has practical ramifications for the development of new food and non-food products and for developing polymers, films and plastics for industrial uses.

'This work is a fundamental change in our knowledge,' said Gary Rabold, vice president for technology transfer, Mid-America Commercialization Corporation. The corporation is responsible for licensing and commercializing intellectual property developed at Kansas State University.

'Now, for the first time, we have a measurable index for dough quality and consistency,' he said. Another immediate impact: the baking industry will be able to replace the chemical improvers it uses for quality control with non-toxic ones. 'Now that we understand that dough enhancers work because they affect tyrosine cross-linking, it will be possible to develop more benign replacement agents for ones now in use,' he noted.

Tyrosine cross-links had gone undetected for so many years partly because no one realised they were there. As Tilley discovered, the tyrosine cross-links are also being affected by the experimental procedures that have been used to prove or disprove the accepted idea of disulfide bond exchange forming dough.

Researchers were unaware that tyrosine cross-links existed in gluten, and so they made inaccurate conclusions based on what they thought was taking place in the dough.

Tilley embarked on an uncharted research direction partly 'through serendipity,' she said. In her studies of a particular wheat protein structure she began noticing a consistent repeat of a certain amino acid sequence. 'That made me wonder why that particular sequence, which contains tyrosine, is being conserved in the wheat plant.'

Curiosity sent her searching the scientific literature where she found research papers about plant proteins with molecular structure strikingly similar, but unrelated, to wheat gluten protein, and those proteins contained tyrosine cross-linking.

'After I read those papers, I had the idea that tyrosine cross-links just might be the structural component that are critical in formation of dough.'

For the next four years, she followed that insight with a series of experiments to test the hypothesis. She isolated the molecules involved, subjected them to various analyses, and was able to demonstrate the existence of tyrosine cross-linking.

The conclusive piece of evidence came when collaborator Om Prakash made NMR images of the physical structure of the purified crosslink.

The research has been supported by the Kansas Agricultural Experiment Station.