ARS | Publication request: Acetone enhances the direct analysis of total condensed tannins in plant tissues by the butanol-HCl-iron assay

Submitted to: American Chemical Society Abstracts
Publication Type: Abstract Only
Publication Acceptance Date: December 20, 2012
Publication Date: N/A

Technical Abstract: The butanol-HCl spectrophotometric assay is widely used to quantify extractable and insoluble forms of condensed tannin (CT, syn. proanthocyanidin) in foods, feeds, and foliage of herbaceous and woody plants. However, this method underestimates total CT content when applied directly to plant material. Through examination of a range of possible co-solvents for the HCl-butanol assay, acetone was identified as a co-solvent which increases anthocyanidin color yields from two forage Lotus species that differ in CT composition. An optimized acetone-butanol-HCl assay with iron (III) gave linear responses with CT standards isolated from Lotus and increased estimates of total CT in herbage and leaves by up to 3.2-fold over the conventional method run without acetone. The use of thiolysis to determine the purity of CT standards further improved quantitation. Comparison of gel-state 13C and 1H–13C HSQC NMR spectra of insoluble residues collected after standard butanol-HCl and the optimized acetone-butanol-HCl hydrolyses revealed that acetone increased anthocyanidin yields by facilitating complete solubilization of CT from plant tissue.