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Protein precipitation behavior of condensed tannins from Lotus pedunculatus and Trifolium repens with different mean degrees of polymerization

Wayne E. Zeller, Michael L. Sullivan, Irene Mueller-Harvey, John H. Grabber, Aima Ramsay, Chris Drake, Ronald H. Brown
Journal of agricultural and food chemistry 2015 v.63 no.4 pp. 1160-1168
Lotus uliginosus, Trifolium repens, alfalfa, bovine serum albumin, chemical precipitation, flowers, leaf protein, leaves, lysozyme, pH, polymerization, proanthocyanidins
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.