Condensed Tannin Concentraton in Sericea Lespedeza as Influenced by Preservation Method

Accurate analysis of condensed tannins in forage is essential to characterize its effect on digestibility. The concentration of analyzable tannins are determined by the forage preservation method. The effect of forage preservation method on condensed tannins was studied in a randomized‐block field experiment with high‐tannin (HT) and low‐tannin (LT) sericea lespedeza, Lespedeza cuneata (Dumont) G. Don. Plants were harvested and fresh frozen (FF), oven dried (OD), freeze dried (FD), and sun cured (SC). Tannin concentrations were determined with a modified vanillin‐HCl procedure. To improve the vanillin‐HCl assay several parameters were examined, including (i) extraction solvents, (ii) effects of water on color reaction, and (iii) assay with purified tannin vs. catechin equivalents. A 7:3 acetone/water solution extracted the greatest amount of tannin for all drying treatments and sericea entries. Color development was greatly reduced with addition of water to the reaction solution. Use of catechin equivalents approximately doubled the estimation of tannin content compared with the purified tannin assay. Tannin concentrations were higher in HT than LT sericea for all preservation method treatments. Averaged across entries, tannin concentrations were 79, 45, 41, and 37 g kg−1 dry matter (DM) for FD, FF, SC, and OD sericea, respectively. Reduced extractability of tannins may be related to increased polymerization of tannins or complexation with other cellular constituents. Freeze drying is the most efficient method of forage preservation for tannin analysis.