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WEST LAFAYETTE, Ind., July 20, 2000 -- Sorghum equals or exceeds many other cereal grains in essential proteins. Unfortunately, too many of the nutrients pass through the body unabsorbed.
Purdue University food science professor Bruce Hamaker has found that each protein body in a single sorghum seed is surrounded by a tough inner protein wall. It takes stomach enzymes longer to break down the wall to reach the nutritional proteins in sorghum than it does to reach the proteins in similar grains, such as corn.
Hamaker's study revealed that in a special sorghum variety, the protein body wall is structured differently, allowing enzymes to digest protein more quickly. Hamaker's findings, which could lead to sorghum crops with greater dietary benefits, were published in the May 9 issue of Proceedings of the National Academy of Sciences. His work also earned Hamaker the 2000 Purdue University Agricultural Research Award.
Sorghum is commonly used as animal feed in the United States, but it more often is consumed by people in other parts of the world. The grain can be an ingredient in snack foods and baking and brewing products, and it sometimes is used as a meat extender. Sorghum contains slightly more calories than corn but fewer grams of fat.
The digestibility problem has mystified agriculturists for years.
"We've recognized this the last 20 years and not known what to do with it," Hamaker said. "If this had been corn, you'd probably have had 20 laboratories working on it."
Associate Dean of Agriculture Randy Woodson said Hamaker's research is adding to what was a small body of knowledge on sorghum digestibility. "There's not been a lot of research done in that area," Woodson said. "Bruce's research has led to the improved nutritional quality of grains, which could have major consumer applications down the road."
Among the cereal grains, sorghum ranks fifth in total world production, behind wheat, corn, rice and barley. Nearly 600 million bushels were harvested in the United States in 1999, from fields in the Southwest and parts of the Midwest. Africa and India also are major sorghum producers.
While sorghum is an excellent source of protein, its shortcomings are well documented. Studies have shown that humans digest only 46 percent of the sorghum they consume, compared with 81 percent of the protein in wheat and 73 percent in corn.
Hamaker's research led him to an uncommon sorghum variety that is 87 percent digestible in laboratory tests. Hamaker said he had a hunch sorghum protein itself played a role in the digestion puzzle. "All along we suspected the protein bodies," Hamaker said, "but we still don't know all we need to know."
Research like Hamaker's is vital to the sorghum industry, said Ray Watson, executive director of the Texas Grain Sorghum Producers, one of the largest sorghum trade groups in the nation. "Our goal is to get into as many markets as we can," Watson said. "And if we can increase the feed grain segment, that's good."
Sorghum is a secondary crop for many growers, Watson said. Many farmers plant sorghum when weather isn't favorable for cotton or wheat. Sorghum thrives in dry climates, he said.
"If we can get the price of sorghum up, we can make sorghum a primary crop," Watson said.
In the coming years, sorghum could find its way onto many Americans' kitchen tables. The absence of gluten, an elastic protein that gives wheat flour its cohesiveness, makes sorghum-based pastas and cereals natural choices for those who are gluten-intolerant.
About one in 250 people is gluten-intolerant, said Jeff Dahlberg, research director for the National Grain Sorghum Producers. That means the condition affects approximately 1 million Americans alone. "Sorghum could take the place of rice or corn for these people," Dahlberg said.
Much of the sorghum research taking place in the United States is sponsored by the International Sorghum/Millet Collaborative Research Support Program. Purdue joined the federally sponsored program -- better known as INTSORMIL -- in the late 1970s. Hamaker has been involved in INTSORMIL research since 1992.
John Axtell, the Lynn Distinguished Professor of Agronomy at Purdue, closely collaborates with Hamaker on sorghum research.
JSL/Ag Hamaker.sorghum
STORY AND PHOTO CAN BE FOUND AT: http://news.uns.purdue.edu/html4ever/0004.Hamaker.sorghum.html
Writer: Steve Leer
Sources: Bruce Hamaker 765-494-5668; hamakerb@foodsci.purdue.edu
Randy Woodson 765-494-8362; wrw@aes.purdue.edu
Other sources:
Ray Watson 806-749-3478; texas@sorghumgrowers.com
Jeff Dahlberg 806-749-3478; jeff@sorghumgrowers.com
Related Web site: National Grain Sorghum Producers: http://www.sorghumgrowers.com
A publication-quality photograph is available at the News Service Web site at http://news.uns.purdue.edu and at the ftp site at ftp://ftp.purdue.edu/pub/uns/. Photo ID: Hamaker.sorghum
ABSTRACT A highly digestible sorghum mutant cultivar exhibits a unique folded structure of endosperm protein bodies
Bruce R. Hamaker, Maria P. Oria, John D. Axtell and Chia-Ping Huang, Purdue University
The endosperm of a sorghum mutant cultivar, with high in vitro uncooked and cooked protein digestibilities, was examined by transmission electron microscopy and alpha-, beta- and gamma-kafirins (storage proteins) were localized within its protein bodies. Transmission electron microscopy micrographs revealed that these protein bodies had a unique microstructure related to high protein digestibility. They were irregular in shape and had numerous invaginations, often reaching to the central area of the protein body. Protein bodies from normal cultivars, such as P721N studied here, with much lower uncooked and cooked digestibilities are spherical and contain no invaginations. Immunocytochemistry results showed that the relative location of alpha- and beta-kafirins within the protein bodies of the highly digestible genotype were similar to the normal cultivar, P721N. Gamma-kafirin, however, was concentrated in dark-staining regions at the base of the folds instead of at the protein body periphery, as is typical of normal cultivars. The resulting easy accessibility of digestive enzymes to alpha-kafirin, the major storage protein, in addition to the increased surface area of the protein bodies of the highly digestible cultivar appear to account for its high in vitro protein digestibility.
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Proceedings of the National Academy of Sciences