Characterization of creaming precipitate of tea catechins and caffeine in aqueous solution.

The content of a crude precipitate formed by creaming, which was made from a catechin mixture and caffeine, was investigated by an integral volume of H-2 proton signals of tea catechins in the (1)H-NMR spectrum. Gallated catechins formed a crude precipitate more predominantly than non-gallated catechins. The 2,3-cis-non-gallated catechin (-)-epicatechin (EC) formed a 1:1 complex with caffeine, and 2,3-cis-gallated catechin (-)-epicatechin gallate (ECg) formed a 2:4 complex with caffeine. The π-π complexation site of EC with caffeine was only the A ring, whereas that of ECg included all aromatic rings, A, B, and B'. It was thought that the hydrophobicity of the 2:4 complex of ECg and caffeine was stronger than that of the 1:1 complex of EC and caffeine, with the result that the 2:4 complex of ECg and caffeine precipitated by creaming more predominantly than the 1:1 complex of EC and caffeine in aqueous solution.