Study on Mechanism of Creaming Down by (-)-Epigallocatechin-3-O-Gallate and Caffeine

<p>When a hot tea beverage cools down, it becomes turbid and brown-white particles settle out. This phenomenon is called a “creaming” or “creaming down reaction”. Previously, Ina et al. reported that creaming down eventually occurs when an aqueous caffeine solution is poured into an aqueous EGCg solution. We therefore attempted to crystallize a crude precipitate formed by creaming, which was made from an aqueous solution of EGCg and caffeine. An aqueous solution of equimolecular amounts containing gallated catechin (-)-epigallocatechin-3-O-gallate (EGCg) and caffeine afforded a crude precipitate by creaming, which crystallized slowly for about three months at 10℃ to give a colorless block crystal. The crystal was determined to be a 2:2 complex of EGCg and caffeine by X-ray crystallographic analysis. The 2:2 complex was formed with the cooperative effect of three intermolecular interactions, π-π and CH-π interactions, and intermolecular hydrogen bonds. Upon formation of the 2:2 complex, a caffeine molecule was captured by a hydrophobic space formed by the aromatic rings A, B, and B’ rings of two EGCg molecules. It was therefore thought that the crude precipitate by creaming occurred from the aqueous solution of EGCg and caffeine due to its high hydrophobicity. </p><p>To confirm the findings, stereochemical structure and intermolecular interaction of complex of EGCg and nicotinamide, which is also one of tea ingredients, were investigated. An aqueous solution containing equimolecular amounts of EGCg and nicotinamide afforded a 2:2 complex of EGCg and nicotinamide. Just like 2:2 complex of EGCg and caffeine, nicotinamide molecules were captured by a hydrophobic space formed by three aromatic rings, A, B, and B’ rings of EGCg in the 2:2 complex of EGCg and nicotinamide. It was considered that EGCg captured various heterocyclic compounds in its aromatic rings, A, B, and B’ rings in aqueous solution. Then the capturing ability of EGCg for various heterocyclic compounds has been investigated.</p>