Comparison of protein precipitation ability of structurally diverse procyanidin-rich condensed tannins in two buffer systems.

The protein precipitation (PP) of bovine serum albumin (BSA), lysozyme (LYS), and alfalfa leaf protein (ALF) by four procyanidin-rich condensed tannin (CT) samples in both 2-[N-morpholino]ethanesulfonic acid (MES) and a modified Goering-Van Soest (GVS) buffer is described. Purified CT samples examined include Vitis vinifera seed (mean degree of polymerization [mDP] 4.1, 16.5 % galloylated), Tilia sp. flowers (B-type linkages, mDP 5.9), Vaccinium macrocarpon berries (mDP 8.7, 31.7% A-type linkages) and Trifolium pratense flowers (B-type linkages, mDP 12.3) and were characterized by 2D NMR (>90% purity). In general, CTs precipitated ALF >LYS≥BSA. PP in GVS buffer was 1 to 2.25 times greater than in MES buffer (25 °C). The GVS buffer system better reflects the results/conclusions from the literature on the impact mDP, galloylation and A-type linkages have on PP. Determinations of PP using the MES buffer at 37 °C indicated that some of these differences may be attributed to the temperature GVS buffer determinations are conducted. In vitro PP studies using the GVS buffer may offer better guidance when selecting CT-containing forages and amendments for ruminant feeding studies.