Kinetics and equilibria of tea fusion - Part 6: The effects of salts and of pH on the concentrations and partition constants of theaflavins and caffeine in Kapchorua Pekoe Fannings
The concentrations of theaflavins and of caffeine in sieved Kapchorua Pekoe Fannings (600–710 μm) have been determined at 80°C with a range of aqueous salt and buffer solutions of ionic strength 0·11 mol dm−3 and of pH 1·9 to 8·3. The caffeine concentration in the infusions and in the leaf, and its partition constant between swollen leaf and solution, was little affected by the presence of electrolytes or pH changes. The concentration of theaflavins in the infusions was not changed by the addition of salts but was considerably greater in acid media and also, temporarily, in borate buffers. The acid effect was corroborated by experiments with a Ceylon Broken Orange Pekoe blend. The most significant finding was that the concentration of theaflavins in the Kapchorua leaf rose markedly with falling pH while its partition constant decreased. These results show that hydrogen ions liberate extra theaflavin by breaking down the leaf structure and/or the bonding of some theaflavin within the leaf. The effect has significant commercial implications since the market price of tea leaf correlates with its theaflavin content.