THE KINETICS OF EXTRACTION OF INDIVIDUAL FLAVANOLS AND CAFFEINE FROM A JAPANESE GREEN TEA (SEN-CHA-UJI-TSUYU) AS A FUNCTION OF TEMPERATURE

Rates of infusion for the four major tea flavanols from a Japanese green tea have been measured for the first time. The results indicate that the ungallated epicatechin and epigallocatechin infuse faster than the gallated flavanols epicatechin gallate and epigallocatechin gallate. The infusion rate is shown to be related to the inverse of the square root of the mass of the molecule. This gives support to the idea that the rate-determining step of the infusion process is a diffusive one. The temperature-dependence of the infusion of the four flavanols yields activation energies of 30 and 50 kJ/mol. In addition, rates of infusion of caffeine from the green tea and its temperature-dependence were investigated. These results indicate that the caffeine infusion rate and the activation energy are significantly larger than for the four flavanols and also larger than for caffeine infusion from black teas. This latter aspect is discussed in terms of differences in manufacturing techniques between black and green tea.