Color reaction of hydrolyzable tannins with Bradford reagent, Coomassie brilliant blue

Bradford protein-binding dye, Coomassie brilliant blue G-250, formed intens ively blue-colored complexes with hydrolyzable tannins. The tannin-dye aggr egates displayed a broad absorption maximum around 700 nm, with a shoulder at 620 nm. Pronounced reactivities were observed with tetra- to nonagalloyl glucoses. Gallic acid, beta-glucogallin and digalloylglucose were inactive and trigalloylglucose gave only a weak reaction. Moderate color formation ( 65% relative to pentagalloylglucose) was observed for the ellagitannin, tel limagrandin II. Monomeric and dimeric proanthocyanidins gave only traces of color. These complexation characteristics parallel the binding of hydrolyz able tannins to proteins. (C) 1999 Elsevier Science Ltd. All rights reserve d.