ARS | Publication request: COMPARISON OF TANNINS FROM SORGHUM: DIFFERENCES IN CHEMISTRY, BIOLOGICAL ACTIVITY AND NUTRITIONAL FACTORS

Submitted to: Meeting Abstract
Publication Type: Abstract Only
Publication Acceptance Date: June 5, 2006
Publication Date: September 17, 2006
Citation: Kaufman, R.C., Bean, S., Tuinstra, M. 2006. Comparison of tannins from sorghum: Differences in chemistry, biological activity and nutritional factors [abstract]. AACC International Meeting. Poster Paper No. 229.

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 are known to bind proteins, limiting their digestibility, as well as having excellent antioxidant potential. Studies were done on seven tannin cultivars grown at the Ashland Bottoms Research Farm in 2003 and 2004. Sorghum cultivars were analyzed for tannin content using a modified vanillin-hydrochloric acid method (MV-HCl). The tannin content of the 14 cultivars tested ranged from 2.3 to 67.2 catechin equivalents (mg/g grain); this range can be attributed to both environmental and genetic factors. To examine the precise impact of tannin content and composition on biological activities (protein binding, protein digestibility, and antioxidant capacity), each of the 14 samples were decorticated to remove the outer 20% of the kernel (bran and testa layer). This bran was mixed at five levels with a base endosperm from a non-tannin sorghum. Pepsin protein digestibility of the reconstituted sorghums ranged from 8% to 58% at the highest tannin levels. The bran fractions were studied for their impact on protein binding and antioxidant capacity. Protein binding ranged from 3.11 to 16.33 mg blue-BSA/g bran. Antioxidant activity ranged from 195.41 to 251.28 umol TEAC. High performance size exclusion chromatography (HP-SEC) was performed on the 14 cultivars to provide detail into the molecular size distribution of the tannin polymers and relationship to tannin functionality. Variation in tannin content and composition were related with differences in tannin functionality. These differences may allow for selections of high tannin sorghums having customized biological activities.