Tannin Analysis in Sorghum Grains
Sorghum (Sorghum bicolor (L.) Moench) contains a wide variety of phenolic compounds and their levels and types depend on the genotype. Sorghums with a pigmented testa contain condensed tannins, which are concentrated in the pigmented testa. In this chapter, three methods of tannin analysis are described: (1) Chlorox bleach test; (2) modified vanillin-HCl assay; and (3) normal-phase high-performance liquid chromatography (NP-HPLC) with fluorescence detection. The Chlorox bleach test is a rapid and inexpensive method that identifies non-tannin and tannin sorghums. The modified vanillin-HCl assay is a colorimetric assay that provides relative tannin values among sorghum samples. The normal-phase HPLC with fluorescence detection separates and quantifies condensed tannins according to their degree of polymerization and confirms the presence or absence of tannins.
Key wordsSorghum Condensed tannins Chlorox bleach test Vanillin-HCl assay Normal-phase HPLC Fluorescence detection
Special thanks to Dr. Tom Herald, USDA-ARS, Center for Grain and Animal Health Research, Manhattan, KS, for providing the sorghum samples for the Chlorox bleach test procedure.
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