SELECTION OF A METHOD OF CONDENSED TANNIN ANALYSIS FOR STUDIES WITH RUMEN BACTERIA

Four colorimetric methods, vanillin-HCl, Prussian blue, 1-butanol-HCl, and H2SO4, were tested for their suitability for measurement of condensed tannins in media used for the culture of rumen bacteria. Of the four, only the H2SO4 procedure was suitable for quantifying condensed tannins in culture media at concentrations used in studies with rumen bacteria. Water reduced the extent of chromophore development in both the vanillin-HCl and 1-butanol-HCl methods. Components in the culture medium resulted in substantial color development in the absence of condensed tannins in both the vanillin-HCl and Prussian blue methods. In contrast, the H2SO4 method was not subject to a loss in chromophore yield from water or to interference from medium components. The chromophore formed was stable, and the assay enabled microgram quantities of condensed tannins to be measured in microbial medium. Condensed tannins in condensed tannin-bovine serum albumin complexes were readily quantified by the H2SO4 method. Thus, the potential exists for the H2SO4 method to quantify condensed tannins in both condensed tannin-bacterial cell and condensed tannin-bacterial enzyme complexes.