Extraction of condensed tannins from cervid feed and feces and quantification using a radial diffusion assay

A radial diffusion assay was employed to quantify condensed tannins (CT) in feed and feces of mule deer (Odocoileus hemionus) and white-tailed deer (O. virginianus). This biological assay measures the precipitation of bovine serum albumin (BSA), with the area of the precipitation ring being proportional to the amount of extracted CT applied to the well. CT extracted from the bark of white spruce (Picea glauca) was used as the standard. CT were extracted with 70% (v/v) aqueous acetone and precipitated with 50% (v/v) aqueous methanol or 70% (v/v) aqueous acetone. Functional range of CT weights for suitable ring measurement was 0.5-4.0 mg, and equilibrium was achieved within an incubation period of 24 hr. Methanol (50%) was a more effective precipitation solvent than acetone (70%) having 13 +/- 4% greater specific activity (P < 0.05) and superior capabilities for predicting CT content. Precipitation rings were evaluated on images magnified on a photocopier. Ring diameters measured on a 200% enlarged photocopy provided the most precise estimate of ring area (R2 = 0.98). This convenient method reduced analysis times and enhanced accuracy and precision of tannin quantification. Analytical consequences and future research requirements are considered.