|MUELLER-HARVEY, IRENE - University Of Reading|
|RAMSAY, AIMA - University Of Reading|
|DRAKE, CHRISTOPHER - University Of Reading|
|BROWN, RONALD - University Of Reading|
Submitted to: Journal of Agricultural and Food Chemistry
Publication Type: Peer Reviewed Journal
Publication Acceptance Date: 11/3/2014
Publication Date: 1/8/2015
Publication URL: https://handle.nal.usda.gov/10113/60308
Citation: Zeller, W.E., Sullivan, M.L., Mueller-Harvey, I., Grabber, J.H., Ramsay, A., Drake, C., Brown, R.H. 2015. Protein precipitation behavior of condensed tannins from Lotus pedunculatus and Trifolium repens with different mean degrees of polymerization. Journal of Agricultural and Food Chemistry. 63:1160-1168.
Interpretive Summary: Condensed tannins are a class of plant components present in a variety of forages including big trefoil, birdsfoot trefoil, and sainfoin. Forages and other plants containing condensed tannins (CTs) have been shown to have an impact on livestock health and productivity including: decrease of protein degradation during the ensiling process, production of a higher level of utilizable escape protein into the hindgut of ruminants, reduction of methane (a greenhouse gas) production during rumination, and reduction of nitrogen waste in manure. These results are purportedly due to protein precipitation induced by the CTs, and they have been shown to be dependent on the size of the CT. Sets of CTs were purified from big trefoil and white clover flowers. From this set, we selected fractions within each species with similar composition and lengths giving us two pairs of CTs: big trefoil (large and medium) and white clover flowers (large and medium) where the average lengths of large and medium CTs were matched. These CTs were tested for their protein precipitation ability against three different proteins. In all cases, the larger CTs were more efficient than the medium CTs in precipitation of protein at rumen pH (~6.5), confirming that CT size plays an important role in protein precipitation and thus plays a strong role in its biological effects. Another result of this study was the development of a new approach to screening CT fractions for purity using nuclear magnetic resonance spectroscopy. These results will help plant breeders with selection for tannin content and structure. They will also help identify plant varieties that are good candidates for genetic modification.
Technical Abstract: The precipitation of bovine serum albumin (BSA), lysozyme (LYS), and alfalfa leaf protein (ALF) by two large- and two medium-sized condensed tannin (CT) fractions of similar flavan-3-ol subunit composition is described. CT fractions isolated from white clover flowers and big trefoil leaves exhibited high purity profiles by 1D/2D NMR and purities >90% (determined by thiolysis). At pH 6.5, large CTs with a mean degree of polymerization (mDP) of ~18 exhibited similar protein precipitation behaviors and were significantly more effective than medium CTs (mDP ~9). Medium CTs exhibited similar capacities to precipitate ALF or BSA, but showed small but significant differences in their capacity to precipitate LYS. All CTs precipitated ALF more effectively than BSA or LYS. Aggregation of CT-protein complexes likely aided precipitation of ALF and BSA, but not LYS. This study, one of the first to use CTs of confirmed high purity, demonstrated that mDP of CTs influences protein precipitation efficacy.