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Protein form and function

A new study is examining protein diversity in Ontario winter wheats so breeders can develop varieties targeted to specific end-uses. Photo courtesy of Jayne Bock, University of Guelph.

Function follows form, when it comes to proteins in wheat. The different structures of various protein molecules are an essential factor in a wheat flour’s ability to produce a specific end-product, whether that’s a cookie, cake, yeast bread, pastry or other product.


So a new project is underway to get a deeper understanding of the proteins in Ontario winter wheats. The resulting information will enable wheat breeders to develop varieties targeted to specific end products, meeting the needs of wheat processors and consumers, and providing Ontario wheat growers with varieties that are in high demand.

The idea for the project emerged when Dr. Jayne Bock talked with several Ontario cereal industry companies to get a sense of the industry’s biggest challenges and issues. “Everything seemed to be coming back to wheat quality, especially the quality of the gluten proteins in the wheat,” says Bock, a food scientist at the University of Guelph and the principal investigator for the project.

“We have been researching wheat quality and gluten proteins in wheat for more than 100 years. The problem is that we’ve primarily focused on hard [western spring] wheats and we have always used bread for the model system. But in Ontario, most of the wheat we produce is soft wheat, especially soft winter wheats. Soft winter wheats typically don’t go into bread products. They typically go into a broad range of products like cakes, crackers, cookies and pretzels,” explains Bock.

“I realized that, from a scientific standpoint, we really didn’t have a good understanding of the gluten proteins and wheat quality for soft wheats. We’ve never taken the time to research what gluten looks like in Ontario hard winter wheats and Ontario soft winter wheats.”

Gluten protein is formed when water is added to wheat flour. As the water is mixed in, the two main types of protein in wheat flour – gliadins and glutenins – start to interact and form bonds, called cross-links, with each other. The resulting cross-linked protein network is gluten. Glutenin helps give gluten its elasticity, while gliadin helps give gluten its extensibility (stretchability). With more mixing or kneading of the dough, more cross-links form, which further changes the structure of the protein network and affects the dough’s behaviour when made into a food product.

“The goal of the project is to gain an understanding of the diversity in Ontario winter wheats right now, and then to use that diversity to understand the protein conformation and gluten quality in Ontario wheat,” notes Bock.

Protein conformation refers to the three-dimensional structure of the proteins. “Typically, proteins have a specific structure to them. For example, the protein structure of hemoglobin in humans is very consistent for the most part,” Bock says. “But wheat is a very heterogeneous biological system and the protein structures in wheat, especially in wheat gluten, can vary quite dramatically because the genetics are so diverse and the types of processing we use to manipulate that structure are quite different.”

Wheat types and varieties have differing protein characteristics. For instance, soft wheats tend to have a lower protein content, form weaker gluten, and have a higher proportion of gliadin, which allows cookie dough to spread. In comparison, hard wheats tend to have a higher protein content, form stronger gluten, and have a higher proportion of glutenin, so they have the elasticity needed for yeast breads.

Bock’s four-year project involves soft red and hard red winter wheats, the two most commonly grown winter wheats in Ontario. It is being funded through the AgriInnovation Program under the Growing Forward 2 platform, with funds from Agriculture and Agri-Food Canada and the Ontario Cereal Industry Research Council.

The project has four objectives. The first is to assess the diversity of proteins that exists in Ontario wheats. Work on this objective is already under way.

The second objective is to examine how the commercial flours made from Ontario wheats perform in various quality tests. Bock says, “Typically, research projects look at the flour from an individual variety of wheat. But from a commercial standpoint, multiple varieties are blended together before the wheat is milled into a flour. To keep this project as commercially relevant as possible, this objective is not to just look at the flour quality from a variety, but to look at the flour quality and behaviour during processing of commercial flour blends from these Ontario wheats.”

The third objective is to develop a safer  alternative to chlorination of cake flour. “Chlorination has some significant personnel safety issues and some environmental safety issues associated with it. So chlorination is eventually going to be phased out,” explains Bock. “When that happens we need to be ready with a suitable alternative to give the same type of flour that we know and love for the cakes that we make.”

According to Bock, chlorination interacts with the starch and the protein in flour and changes the way they behave. The result is a flour especially suited for making cakes.

“Chlorination essentially oxidizes the starch granule and gives it some unique properties. It’s the starch granule when it gelatinizes during baking that will give the cake its structure,” she says.

“And chlorination changes the gluten proteins in such a way that they can’t come together and form a network. People will often say ‘the proteins are rendered non-functional.’ But the proteins are still there, and they still provide thickening to a batter that keeps the starch granules from settling before you get it in the oven to bake it.”

In this objective, Bock will be trying to recreate these starch and protein changes in a non-chlorinated flour.

The project’s fourth objective is to examine wheat and flour aging. Aging affects various characteristics of wheat grain and flour, including the gluten, so adequate aging is important for flour quality and baking performance. This objective will focus on predicting and controlling aging so wheat processors will be able to more reliably get the quality they need.

Bock says, “When wheat is harvested, it doesn’t stop changing – that’s really only the beginning of changes in the wheat grain and then the milled flour over time. That is not always very well understood and can cause some problems for processors.”

Wheat needs to be stored for a time before milling, but the exact length of time can vary. “We call this period the sweating period.

The wheat is changing substantially during that time. If you try to mill it during those weeks, it’s very difficult and you don’t get the same quality of flour out of it. The wheat grain has to mature to a certain extent to give consistent milling properties,” she notes.

“Then, once you mill a grain, it is exposed to oxygen and the atmosphere, and the oxygen reacts with the proteins, causing changes in the protein fraction.”

She adds, “Eventually the grain before milling and the flour after milling each reach a point where further changes are very minimal and the b ehaviour and the quality remain consistent for quite some time. However, [the flour] eventually drops out of that equilibrium phase. You reach a point when the flour’s behaviour is not consistent anymore. So you can’t reliably use it and expect to see the same product after it has aged for too long.”

Value chain benefits
Bock aims to tie together all the information resulting from the project’s four components to develop “a rough working model of what the gluten network and gluten behaviour looks like in Ontario winter wheats. We can use that model to guide our decisions about aiming specific varieties for specific types of processes and products.”

“By looking at the diversity that is already in Ontario wheats and then coupling that with all the other activities, we aim to give wheat breeders an opportunity to see where is the diversity and how can you use that in a more targeted breeding strategy. Because ultimately, you want to breed wheat varieties with good disease resistance, good insect pest resistance, and good yields – and that end-users are going to value and use,” explains Bock.

“We’re hoping that eventually certain varieties can be targeted for certain types of products. It’s not necessarily an identity-preserved type of system, but the end-users will see added value in those varieties that are most suitable for their product. With Ontario being one of the major soft wheat producing regions in North America, this will provide benefit and value to the entire market value chain from the breeders all the way through to the end-users.”

 


November 13, 2014
By Carolyn King

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