Acetone Enhances the Direct Analysis of Total Condensed Tannins in Forage Legumes by the Butanol-HCl Assay.

Depending on concentration, condensed tannins (CT) in forages can enhance, impede or have no effect on protein utilization and performance of ruminants. Defining optimal CT levels has been elusive, partly because current methods for estimating total soluble plus insoluble CT are laborious or inaccurate. In this study, various co-solvents were evaluated for enhancing CT recovery and quantitation during rapid direct analysis of plant tissues by the widely used butanol-HCl method. Among the co-solvents evaluated, acetone proved most effective for consistently increasing anthrocyanidin yields from CT standards and particularly plant tissues. When used in conjunction with appropriate CT standards, amending butanol-HCl with 400 mL/L acetone increased tissue CT estimates from 13.3 to 34.2 g/kg in Lotus corniculatus and from 21.4 to 69.4 g/kg in Lotus uliginosus. Adding additional acetone to L. corniculatus reduced anthrocyanidin yields from standards without affecting tissue yields. Conversely, additional acetone increased anthrocyanidin yields from L. uliginosus tissue without affecting standards. Amending butanol-HCl with acetone did not alter CT estimates for neutral-detergent fiber (NDF). Thus acetone may partly act by enhancing CT accessibility during butanol-HCl hydrolysis, consistent with the widespread use of aqueous acetone for isolating soluble CT from plant tissue. Among other variables examined, running L. uliginosus standards with tannin-free tissue or NDF from Medicago sativa slightly reduced anthrocyanidin yields as did running assays of tissues from either Lotus with a smaller volume of reagent. Thus, conditions for CT assays should be optimized for each type of plant material.