Structural features of condensed tannins and their impact on bioactivities

• Main Author: Ropiak, Honorata M.
• Published: University of Reading 2017
• Online Access: https://ethos.bl.uk/OrderDetails.do?uin=uk.bl.ethos.749292

Condensed tannins (CT) are bioactive plant compounds found in various fruits, vegetables, medicinal plants and forages. In the right concentration, CT have a beneficial impact on human and animal nutrition, health and welfare. In recent years, there has been a focus on their anti-parasitic effects against gastrointestinal nematodes. These effects are believed to be caused by CT-protein interactions, which are widely studied to better understand dietary protein utilisation by ruminants. To study their bioactivity, CT from medicinal plants and herbal products were isolated, quantified and analysed for their key characteristics: galloylation and A-type content, procyanidin/prodelphinidin ratios, cis-/trans-flavan-3-ol ratios and the mean degree of polymerisation, which gives an indication of the average molecular weight. For the first time this analysis was done for a large panel of contrasting CT. From this panel, the interaction of CT with model proteins bovine serum albumin (BSA) and gelatin was studied. It was demonstrated that CT average size was strongly correlated with the aggregation of BSA and gelatin. Interactions of CT with BSA were driven by the presence of procyanidins and to lesser extent by the presence of cis-flavan-3-ols. The secondary protein structure was most significantly changed by the presence of prodelphidinins in CT. Structure-bioactivity of CT was investigated against motility of adult Caenorhabditis elegans, which is a model of gastrointestinal parasitic nematodes. It was observed that the prodelphidin content was correlated with the inhibition of nematode motility. CT fractions insoluble in aqueous solutions had a very high nematocidal effect. The highest damage to the cuticle was caused by prodelphidinin-containing CT and galloylated procyanidins. Galloylated procyanidins and cinnamaldehyde, a common feed additive, show a significant synergistic effect.