Activity, Purification and Analysis of Condensed Tannins.

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), exhibit a variety of biological effects on ruminants and to the dairy farm nitrogen cycle. Interest in CTs stems from the potential positive impact they could bring to the agricultural industry due to their ability to modulate proteolysis during forage conservation and ruminal digestion, in the prevention bloat, to reduce intestinal parasite burdens, abate methane and ammonia emissions from ruminants and inhibit the activity of soil nitrifying bacteria. The current theory on 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. Examination of CT-protein interactions in in vitro experiments has the ability to shed light on how CT structure affects function in each of these biological effects. However, to perform these studies requires obtaining sufficient quantities of well-characterized CTs of high purity from the plant source under investigation. The purification of CTs from a variety of plant material was conducted through the use of Sephadex LH-20 resin and the structure and purity of these samples were confirmed through two-dimensional nuclear magnetic resonance spectroscopy (2D NMR) and thiolysis. Analysis of some structural features of CT by 2D NMR techniques is straight forward whereas other intricacies of CT structures remain elusive. Alternative methods for CT structural analysis and content will also be summarized. The presentation will conclude with a listing of the questions yet to be answered and obstacles present in the path forward relating in vitro observations to results obtained from in vivo studies.