Getting rid of gray discoloring in foods such as fresh noodles, breads, and refrigerated biscuits is now possible, thanks to a new white hard wheat breeding line developed by USDA scientists in Lincoln.

Plant geneticist Robert Graybosch, research leader at the USDA Agricultural Research Service’s (ARS) Grain, Forage, and Bioenergy Research Unit in Lincoln, developed a wheat that has no polyphenol oxidase—an enzyme present in all plants that causes discoloring. The enzyme causes browning in sliced apples, black spots in cut avocados, and dark marks on banana peels.

Robert Graybosch

Key Facts

• Polyphenol oxidase is a natural enzyme in plants.
• It turns cut apples brown and some wheat products gray.
• ARS scientists developed a wheat with almost no polyphenol oxidase.

“A lot of U.S. white wheats still have high levels of polyphenol oxidase,” Graybosch says. “To have a successful white wheat for both the export market and the domestic market, milling companies want low or no polyphenol oxidase.”

Graybosch, who has a joint appointment as an adjunct professor in the UNL Department of Agronomy and Horticulture,  has been studying the polyphenol oxidase trait in wheat for the last 15 years, investigating numerous samples of white wheat. Collaborating with the University of Nebraska–Lincoln and Montana State University, in 2000 Graybosch screened more than 3,000 wheat lines for polyphenol oxidase and then mated wheats with different forms of the genes that produced this enzyme.

The new wheat line, 070R1074, was developed by crossing two Australian wheats entered into the ARS National Small Grains Collection in the 1930s. 

“For 70 years, these two Australian wheats have been in the germplasm collection with this trait of interest and economic importance that the milling industry and exporters need and want,” Graybosch said. “This demonstrates the value of this diversified wheat collection. You don’t always know what you have until you do something with it.”

In their research, Graybosch and his colleagues discovered naturally occurring genetic mutations in the new wheat line, which resulted in nearly complete loss of polyphenol oxidase activity.

The newly developed line used to charaterize the gene and enzyme activity is a spring wheat and not suitable for cultivation in Nebraska, where winter wheat is grown.

"We are working to introgress the trait into winter wheat backgrounds, and have the first winter wheats for selection in the field at the ARDC near Mead," Graybosch said.

Although some low-polyphenol oxidase hard winter white wheats have already been developed, many U.S. white wheats still have high levels of polyphenol oxidase, according to Graybosch. High polyphenol oxidase levels make U.S. producers less competitive in domestic and export markets.

In Asia, hard white wheat is popular for making products such as fresh noodles, and white whole grain breads are gaining favor in the United States. To be competitive, U.S. milling companies need wheats with low or no polyphenol oxidase. 

Read more about this work in the April 2016 issue of AgResearch, an online magazine about USDA Research. ARS is USDA’s principal intramural scientific research agency.