Measurement of Thermodynamic Constants of Amino Acids, Ployphenols and Caffeine in Green Tea

Abstract

The partition constants of amino acids, polyphenols and caffeine of green tea during extraction were measured at 92.5 and 80.0°C according to M. SPIRO'S two-phase model. The enthalpy changes of these constituents during extraction were calculated.
At equilibrirum, the concentrations of these three constituents in swollen tea leaf were larger than those in solution. When determining the contents of these constituents, if the amounts in swollen tea leaf compared with those in solution are larger than the permissible errors, the amounts in swollen tea leaf are not negligible. It is necessary to calculate the real content with the partition constant and the concentration in solution as the result.
The enthalpy changes of amino acids, polyphenols and caffeine during extraction are 10.7, 9.4 and 17.7 KJ/mol, respectively, It suggests that the extractions of these three constituents are endothermic processes. At higher temperature, the partition constants are larger and it is advantageous to extraction.