Activity, Purification, and Analysis of Condensed Tannins: Current State of Affairs and Future Endeavors

Abstract

As a class of plant polyphenolic compounds contained in some forages (i.e., sainfoin [Onobrychis viciifolia Scop.], big trefoil [Lotus pedunculatus Cav.], birdsfoot trefoil [Lotus corniculatus L.]), condensed tannins (CTs), also referred to as proanthocyanidins (PAs or PACs), exhibit a variety of biological effects on ruminants. The potential positive impact of CTs on the agricultural industry stems from their ability to modulate proteolysis during forage conservation and ruminal digestion, to prevent bloat, to reduce intestinal parasite burdens, to abate methane and ammonia emissions from ruminants, and to inhibit the activity of soil‐nitrifying bacteria. How CTs exert these effects on ruminants focuses on the interaction of CTs with proteins. The structure‐activity relationship in CT–protein interaction is not well understood but is known to be dependent on the structure and properties of both the CT and the protein. The purpose of this perspective is fivefold. First, we provide the reader with a better understanding of the structural diversity of CTs present in plant material and enable the reader to appreciate that not all CTs are the same. Second, we provide examples of how CT structural diversity affects the interaction of CTs with the protein, which, in turn, dictates the biological response from the animal. Third, we describe the hurdles in obtaining highly pure and well‐characterized CTs from natural sources for use in studies to attempt to elucidate how CTs impart each biological effect. We then describe improved and emerging techniques for CT analysis and, finally, we conclude this perspective with questions to address in future investigations and forward a list of recommendations for CT researchers to follow.

Benefits of Condensed Tannins in Forage Legumes Fed to Ruminants: Importance of Structure, Concentration, and Diet Composition

“…Current thinking suggests that these secondary metabolites provide plants with a plasticity that can support their development and interaction with the environment (Bidel et al, 2010;Neilson et al, 2013;Mouradov and Spangenberg, 2014). It is important to appreciate that a multitude of different CT compounds exist (Khanbabaee and van Ree, 2001;Hümmer and Schreier, 2008;Salminen and Karonen, 2011;Zeller, 2019), and that their synthesis in the plant kingdom has not converged on a single structure. For example, Chen et al (2014) showed that the temperatures experienced by the mother plant elicit CT pathways that can pass information to the next generation.…”

“…We emphasize that the widely used elution of plant extracts with 70% aqueous acetone from Sephadex LH-20 columns for tannin "purification" can lead to CT concentrations as low as ~13 g CTs 100 g −1 "purified sample" (Williams et al, 2014b). Thiolysis or phloroglucinolysis (analytical degradation of CTs with thiols or phloroglucinol) can be used to determine the composition of CTs by depolymerization, enabling characterization of the flavan-3-ol subunits (Zeller, 2019). (Gea et al, 2011;Pérez-Jiménez and Lluís Torres 2011;Cheynier et al, 2015;Hixson et al, 2016;our unpublished data).…”

“…Procyanidins are composed of catechin or epicatechin and prodelphinidins of gallocatechin or epigallocatechin subunits (for further details, seeZeller, 2019). Procyanidins are composed of catechin or epicatechin and prodelphinidins of gallocatechin or epigallocatechin subunits (for further details, seeZeller, 2019).…”

“…Example of a condensed tannin (CT) molecule that consists of four flavan-3-ol subunits (= monomeric building blocks). Procyanidins are composed of catechin or epicatechin and prodelphinidins of gallocatechin or epigallocatechin subunits (for further details, see Zeller, 2019). a few CT-containing feeds with ruminant animals (e.g., sheep, goats, and cattle;Mueller-Harvey, 2006;Waghorn, 2008).…”

The Value of Condensed Tannins in Forages: Overview of the Symposium

“…Wayne Zeller from the US Dairy Forage Research Center in Madison, WI, reported on the activity, purification, and analysis of CT (Zeller, 2019). Wayne Zeller from the US Dairy Forage Research Center in Madison, WI, reported on the activity, purification, and analysis of CT (Zeller, 2019).…”