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Improving Soybean Digestibility

MADISON, Wisc. — Soybean is one of the most important economic crops in the U.S., an essential component of a number of commercial products, including soybean meal used as animal feed. The development of these feed products has had some obstacles due to the carbohydrates that make up the soybean, but new research may have discovered a way to improve the use of soy as a feedstock. Results of the study were published in the November 2008 issue of The Plant Genome.

The usefulness of the meal is determined, in part, by the carbohydrate component, which is comprised of three major sugars: sucrose, raffinose, and stachyose. Of the three, only sucrose is nutritionally useful and can be fully digested by monogastric animals. Removing raffinose and stachyose from soybean meal has been reported to increase the energy of the diet by as much as 20%.

"Although targeted at improved digestibility in animal feeds, removing these compounds from soybean meal could also improve consumer products, such as soymilk," said Kristin Bilyeu, USDA-Agricultural Research Service and lead researcher.

Researchers Bilyeu and Emily Dierking, members of the Interdisciplinary Plant Group at the University of Missouri, believe that the nutritive value of soybean meal can be increased by disrupting the activity of raffinose synthase to reduce the levels of raffinose and stachyose. The reduced activity of this enzyme allows sucrose to accumulate in the seed; the accumulation of additional sucrose along with the decrease in raffinose and stachyose will increase the metabolizable component of the meal at the expense of non-nutritional components.

"This project demonstrates a translation of information from model systems and basic research to crops to the finished seed composition," said Bilyeu.

The researchers show that the candidate raffinose synthase gene RS2 completely associates with the seed raffinose phenotype through a segregating population. They conclude that identification of a soybean raffinose-synthase candidate gene which completely associate with the low raffinose and stachyose phenotype will enable increased breeding efficiency of this desirable trait into soybean varieties.