|NAUMANN, HARLEY - University Of Missouri|
|SEPELA, REBECKA - Miami University - Ohio|
|REZAIRE, AIRE - Miami University - Ohio|
|MASIH, SONIA - Miami University - Ohio|
|ROBE, JAMISON - University Of Wisconsin|
|HAGERMAN, ANN - Miami University - Ohio|
Submitted to: Molecules
Publication Type: Peer Reviewed Journal
Publication Acceptance Date: 8/21/2018
Publication Date: 8/23/2018
Citation: Naumann, H., Sepela, R., Rezaire, A., Masih, S.E., Zeller, W.E., Reinhardt, L.A., Robe, J.T., Sullivan, M.L., Hagerman, A.E. 2018. Relationships between structures of condensed tannins from Texas legumes and methane production during in vitro rumen digestion. Molecules. 2018, 23, 2123. https://doi.org/10.3390/molecules23092123.
Interpretive Summary: Condensed tannins belong to a group of molecules called polyphenols which naturally occur in some plant species. The presence of condensed tannins in forages, or added to total mixed rations, have been shown to reduce the production of methane during ruminant digestion. In addition to inhibiting production of this potent greenhouse gas, a significant amount of energy is required for the production of methane by ruminant. Inhibition of methane production conserves this energy which then can be used by the animal, increasing energy use efficiency. Although significant research has been conducted in this area, thus far, there is no known correlation of condensed tannin structure with its ability to inhibit methane production in ruminant animals. In this study, purified condensed tannins from nine warm-season perennial legumes were examined by advanced analytical techniques in order to determine the composition and structure of the condensed tannins. No strong correlation was observed between methane production and the protein precipitation capabilities of the condensed using three different proteins (bovine serum albumin, lysozyme and alfalfa leaf protein) at the pH of the rumen. The modulation of methane production could not be correlated to condensed tannin structure (hydroxylation pattern, stereochemistry and extent of modification by gallic acid). However, a strong non-linear correlation was observed for the inhibition of methane production versus the antioxidant activity in plant sample in a series of structure typically observed in forage condensed tannins. The findings from these laboratory experiments suggest that the antioxidant activity of the forages (from condensed tannins and non-condensed tannin antioxidants) may play a primary role in mitigation of methane production in ruminants and provide a unique approach to the study of the mechanism of methane production during ruminant digestion. Assessing the antioxidant activity of forages and feedstuffs consumed by ruminants could provide a predictive model for methane production during ruminant digestion.
Technical Abstract: Previous studies showed that a series of purified condensed tannins (CTs) from warm-season perennial legumes exhibited high variability in their modulation of methane production during in vitro rumen digestion. The molecular weight differences between these CTs did not provide correlation with either the in vitro CH4 production or the ability to precipitate bovine serum albumin. In an effort to delineate other structure-activity relationships from these methane abatement experiments, the structures of purified CTs from these legumes were assessed with a combination of methanolysis, quantitative thiolysis, high resolution 1H-13C HSQC NMR spectroscopy and ultrahigh resolution MALDI-TOF MS. The composition of these CTs is very diverse: procyanidin/prodelphinidin (PC/PD) ratios ranged from 98/2 to 2/98; cis/trans ratios ranged from 98/2 to 33/66; mean degrees of polymerization ranged from 6 to 39; and % galloylation ranged from 0 to 75%. No strong correlation was observed between methane production and the protein precipitation capabilities of the CT towards three different proteins (BSA, lysozyme and alfalfa leaf protein) at ruminal pH. However, a strong non-linear correlation was observed for the inhibition of methane production versus the antioxidant activity in plant sample containing typical PC- and PD-type CTs. The modulation of methane production could not be correlated to CT structure (PC/PD or cis/trans ratios and extent of galloylation). The most active plant in methane abatement was Acacia angustissima, which contained CT that presented an unusual challenge as it was resistant to standard thiolytic degradation conditions and exhibited an atypical set of cross-peak signals in the 2D NMR. The MALDI analysis supported a 5-deoxy flavan-3-ol-based structure for the CT from this plant.