New Clues to Wheat Hardness

Scientists are a step closer to understanding the chemistry behind the hardness of wheat kernels, thanks to work at the Western Wheat Quality Laboratory in Pullman, Washington.

"Hardness is perhaps the single most important trait relating the grain to its end use," says ARS chemist Craig Morris, who heads the laboratory. "Many properties of wheat flour that are important to manufacturers, such as water absorption, depend on the initial hardness or softness of the grain."

Bakers use hard wheat for bread and soft wheat for cakes, cookies, and some noodles.

But the division between hard wheat and soft is not always clear cut, Morris says. Pacific Northwest growers, for example, produce soft white wheat that's popular in Asia. But some companies in the United States have said the same soft wheat is too hard.

To resolve such discrepancies, Morris says that researchers need to understand hardness on a fundamental level. Morris' latest discovery may help. He milled wheat into flour and separated the starch from gluten and other compounds.

Morris found that starch from soft wheat always contains polar lipids—a specific type of fat—attached to the surface of the starch molecules. Few or none of these lipids attach to hard wheat starch.

"This gives us a biochemical marker to identify soft and hard wheats. If the polar lipids are attached, the starch is from soft wheat," he says.

Polar lipids are the second such discovery. A team of researchers from the United Kingdom found in 1986 that a group of proteins called friabilins were also perfectly associated with soft but not hard wheat. Morris' research indicates that the two findings are related. The friabilin proteins seem to bind to the lipids rather than to the starch itself.

"When we determine what role these two compounds play in creating soft wheat, we should be better able to develop custom-tailored wheat," he says. -- By Kathryn Barry Stelljes, ARS.

Craig F. Morris is at the USDA-ARS Western Wheat Quality Laboratory, Washington State University, Johnson Hall, Room 209, Pullman, WA 99164-6420; phone (509) 335-4062.