Activity, purification, and analysis of condensed tannins: current state of affairs and future endeavors

Authors: Zeller, Wayne

Submitted to: Crop Science
Publication Type: Peer Reviewed Journal
Publication Acceptance Date: 3/19/2019
Publication Date: 5/16/2019
Citation: Zeller, W.E. 2019. Activity, purification, and analysis of condensed tannins: current state of affairs and future endeavors. Crop Science. https://doi.org/10.2135/cropsci2018.05.0323.
DOI: https://doi.org/10.2135/cropsci2018.05.0323

Interpretive Summary: Condensed tannins (CTs) are a class of compounds contained in some plants that exhibit a variety of biological effects on ruminant animals such as dairy cows. Their positive effects include an ability to inhibit forage protein breakdown during the ensiling process and also during digestion in the rumen. Consumption of CT-containing plants is also known to help prevent bloat, help control the level of intestinal parasites, and reduce methane and ammonia emissions from ruminants. How CTs exert these effects on ruminants is focused 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. Examination of CT-protein interactions in laboratory experiments has the ability to shed light on how CT structure affects function in each of these effects. However, to perform these studies requires obtaining sufficient quantities of well-characterized CTs of high purity from the plant source under investigation. This paper describes the efforts being taken to accomplish this goal, as well as the new and improved techniques being developed to characterize the CTs. The paper concludes with questions yet to be answered and current obstacles in relating the observations seen in a lab to results obtained from animal studies.

Technical Abstract: As a class of plant polyphenolic compounds contained in some forages (i.e., sanfoin, big trefoil, birdfoot trefoil), 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, abate methane and ammonia emissions from ruminants, and inhibit the activity of soil-nitrifying bacteria. How CTs exert these effects on ruminants is focused 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. Examination of CT-protein interactions in in vitro experiments may shed light on how CT structure affects function. However, performance of these studies requires obtaining sufficient quantities of well-characterized CTs of high purity from the plant source under investigation. This paper discusses the steps being taken to accomplish this goal. New and improved analytical techniques that are being developed to characterize CTs are also outlined. The paper concludes with questions yet to be answered and current obstacles in relating in vitro observations to results obtained from in vivo studies.