Nanoparticles in plant extracts--factors which influence the formation of nanoparticles in black tea infusions.

The influence of different factors on the formation of nanoparticles in freshly brewed tea extracts was investigated. A black tea infusion was observed during cooling using photon correlation spectroscopy (PCS). The mean particle size and the number of the nanoparticles increase with decreasing temperature. In the presence of caffeine more particles are formed within the infusion. To study the influence of slight structural differences between methylxanthines, the effect of the addition of caffeine to solutions of freshly prepared decaffeinated tea was compared to that of theophylline and theobromine. In the case of theophylline fewer nanoparticles were formed. Molecular modelling calculations were performed to evaluate the most probable geometries for caffeine-polyphenol complexes. A parallel position and a congruent orientation of the 6-membered ring of caffeine and the aromatic galloyl group is the most probable geometry.