Determination of theaflavins in tea solution using the flavognost complexation method
Several aspects of the flavognost method for determining theaflavins (TF) in tea solutions have been quantitatively investigated. Double extraction experiments showed that the partition coefficient of TF between water and isobutyl methyl ketone (IBMK) is 4.15 and approximately independent of temperature. The efficiency of the extraction step using 2 volumes of IBMK to 1 volume of tea infusion is then equal to 89%. A structure has been proposed for the green complex formed between the extracted TF and flavognost in a 25% VNIBMK - 75% WVethanol mixture, and the equilibrium constant for its formation at 25 "C was found to be 0.073. The normal analytical procedure thus leaves 45% of TF uncomplexed. As only 85% of the TF in a sample of tea solution eventually appears in the form of the green flavognost complex, it is important not to vary the standard analytical procedure.