X-rays light the way to more nutritious flour

Marie Freebody, marie.freebody@photonics.com

Cereals, breads and pasta could be produced from wheat grain containing higher amounts of essential minerals with a little help from x-ray vision. High-intensity x-rays from the world-famous Diamond Light Source synchrotron in Oxford usually are used to observe metal distribution and chemistry in various samples. Now, however, the powerful x-rays are being redirected to carry out fluorescence analysis of wheat varieties.

Shown is a red-green-blue overlay of manganese, zinc and iron distribution in a cross section of wheat grain. Mineral distribution is limited to the bran and germ (observed as the large structure at the bottom of the grain). No minerals are identified in the white flour.

Scientists at Rothamsted Research, an institute of the Biotechnology and Biological Sciences Research Council (BBSRC), hope that their studies of wheat could be used to grow potentially life-saving mineral-enriched flour.

“Iron and zinc deficiency has been estimated by the World Health Organization to affect billions of people worldwide, with deaths totaling over 1 million people every year,” said Dr. Andrew Neal, who leads the BBSRC-funded project. “These deficiencies arise not because of a lack of minerals in soils, but because wheat and other cereals lay down only limited amounts of minerals in grain tissue. By increasing the amount of minerals that plants allocate to the grain, a more nutritious staple diet could be provided, and many of these deaths could be avoided.”

This heat map representation is based upon fluorescence intensity (blue, low; red, high) of minerals in a cross section of wheat grain. Again, the distribution of minerals – manganese (Mn), zinc (Zn), iron (Fe), nickel (Ni) and copper (Cu) – is limited to the bran and germ (observed as the large structure at the bottom of the grain). Images courtesy of Dr. Andrew Neal.

Most of the mineral content of grain is contained in the bran and germ, but when grain is milled to produce white flour, much of the mineral content is lost and therefore missing from our diet. By studying the mineral contents and distribution in grain, the new technique will identify grain varieties that contain increased levels of minerals in the white flour. These new varieties can then be used to develop new commercially available wheat.

At the same time, newly developed varieties that do not contain increased flour-associated minerals can be identified rapidly so that further experimental effort is not wasted on them.

So far, the Rothamsted team has developed techniques of sectioning and visualization that use highly focused x-ray beams to image the distribution of minerals via x-ray fluorescence. This means that distribution data can be collected on a number of minerals simultaneously.

Until now, the only approach was to stain a limited number of minerals one at a time and to observe grains microscopically. “Not only can we now observe many elements in a single grain, we are also able to interrogate the complexation of each mineral,” Neal said. “Mineral complexation is important because it determines the bioavailability – digestibility – in the grain.”

The synchrotron-based approach provides a relatively rapid method of visualizing the mineral distribution within current and new grain varieties. In the imaging process, the synchrotron accelerates and directs electrons at speeds very close to the speed of light to provide high-intensity x-ray beams.

Wheat grains are sectioned and mounted in epoxy resin at a 45° angle to the incident x-rays on an X-Y-Z stage. The sample then is moved in a stepwise manner so that its fluorescence is collected at discrete points, enabling eventual study of the whole sample.

“The fluorescence intensity due to each element in the sample is analyzed by software, and the resulting two-dimensional maps are produced,” Neal said. “We have studied two new grain varieties that contain three times as much iron as current wheat varieties. However, fluorescence mapping has detected that the additional iron is stored in the bran of both varieties but is not transported across the bran into the white flour.”

In the next stage of analysis, Neal and colleagues hope to determine not only which cells are preventing the further transport of iron but also the iron chemistry in the cells. This information will be of great use to plant breeders who can employ the Rothamsted results to develop new varieties in which iron transport into the white flour is not limited.