They might be called a blessing or a curse – tannins, which are present in certain sorghums, contain health-promoting antioxidant properties, but also provide a bitter taste and decreased protein digestibility. To better understand tannins, their role in sorghum and how they can be altered to improve sorghum’s use as food and feed, a team of scientists led by Kansas State University and U.S. Department of Agriculture researchers, has cloned the tannin gene in sorghum.

Tannins’ high antioxidant, anti-inflammatory and UV-protective functions promote human health, and recent studies show they can be a tool in fighting obesity because they reduce digestibility, said Jianming Yu, associate professor of agronomy at K-State. Tannins in sorghum also provide a natural chemical defense against bird predation and bacterial and fungal attack in the field.

On the other hand, tannins provide a bitter taste to some foods and decrease protein digestibility and feed efficiency in humans and livestock.

The team was led by Yu, along with Tesfaye Tesso, K-State sorghum breeder and associate professor of agronomy, and Scott Bean, scientist with the U.S. Department of Agriculture-Agricultural Research Service (USDA-ARS) and adjunct faculty in K-State’s Department of Agronomy.

The researchers’ study, “Presence of tannins in sorghum grains is conditioned by different natural alleles of Tannin1” (http://www.pnas.org/content/109/26/10281.abstract) was published in the June 26 issue of the Proceedings of the National Academy of Sciences of the United States of America (PNAS).  

Sorghum is an old-world cereal grass that serves as a dietary staple for more than 500 million people in more than 30 countries, Yu said. In 2011, the United States was the No. 1 exporter of sorghum on the world market and the No. 2 producer (behind Nigeria), according to the U.S. Department of Agriculture. In 2011, Kansas produced 110.0 million bushels – 51 percent of the total U.S. crop. Sorghum production in the U.S., primarily for the feed industry, uses non-tannin sorghum hybrids.

Unlike many plants which employ C3 photosynthesis that uses water, carbon dioxide and solar energy to synthesize sugars, sorghum, which performs a modified form called C4 photosynthesis, has adapted to hot environments.

“One key reason to study tannins is to untangle their relationship with cold tolerance, a key agronomic trait to improve sorghum. The work is ongoing,” said sorghum breeder Tesso. An earlier screening work found that a high proportion of cold tolerant sorghum lines contain tannins.