ARS | Publication request: Improved Characterization of Sorghum Tannins Using Size-Exclusion Chromatography

Submitted to: Cereal Chemistry
Publication Type: Peer Reviewed Journal
Publication Acceptance Date: May 3, 2009
Publication Date: July 1, 2009
Citation: Kaufman, R.C., Tilley, M., Bean, S., Tuinstra, M.R. 2010. Improved Characterization of Sorghum Tannins Using Size-Exclusion Chromatography. Cereal Chemistry. 86(4):369-371.

Interpretive Summary: Tannins are polymers of phenol ring containing molecules that have antioxidant properties which are found in many types of plants. Some sorghum lines produce tannin in their grain at a level higher than that found in blueberries. The tannin composition may play a significant role on influencing the tannin functionality. There is a wide range of tannin levels found in the tannin producing sorghum lines and it is useful to identify and quantify the tannin content. Several methods have been developed for characterization of tannins from different plants using a variety of techniques. Most of the methods are very time and resource consuming, however some provide a rapid separation of the tannin polymers using a relatively easy procedure. High performance size exclusion chromatography (HP-SEC) was used to characterize tannins from seven sorghum cultivars grown over two years to provide detail into the molecular size distribution of the tannin polymers. Area under all of the tannin peaks was highly correlated (r = 0.95) to the tannin content of the sorghum bran fractions in high and low tannin sorghum lines.

Technical Abstract: Tannins are large polyphenolic polymers consisting of flavan-3-ol subunits that are deposited in the pigmented testa layer of sorghum kernels. Tannins have been characterized in several different species of plants using a multitude of techniques. Most of the methods are very time and resource consuming, however some provide a rapid separation of the tannin polymers using a relatively easy procedure. High performance size exclusion chromatography (HP-SEC) was used to characterize tannins from seven sorghum cultivars grown over two years to provide detail into the molecular size distribution of the tannin polymers. Substantial differences were seen in the peak area % of several peaks across the seven cultivars. The total peak area was strongly correlated (r = 0.95) to the tannin content of the sorghum bran fractions. An estimation of the DP for certain peaks were shown based on comparison to previous studies. The tannins ranged from a DP of 2 to 22. The tannin composition may play a significant role on influencing the tannin functionality. These differences may allow for selection of sorghums with differing compositions to fit different applications.