Formation of Radicals and Chemiluminescence during the Autoxidation of Tea Catechins.

Abstract

Four catechins, ( -)-epicatechin (EC), ( -)-epigallocatechin (EG), ( -)-epicatechin gallate (ECg) and (-)-epigallocatechin gallate (EGg), extracted from tea were investigated with respect to the formation of radicals and chemiluminescence during autoxidation. An alkaline solution (0.05 n NaOH) of these catechins indicated ESRabsorption accompanying a browning reaction. The spectra of EG and EGgshowed a double triplet at the early stage of autoxidation, but the intensity of each decreased rapidly and the shape of the spectra changed with time, suggesting that most of the radicals disappeared and some changed into others. The spectrum of ECg showed a triplet of relatively strong intensity but decreasing slowly. EC exhibited a very weak spectrum due to EG and EGg being present as impurities. From these results, it was concluded that radicals were easily formed on the aromatic ring to which three hydroxyl groups are attached. The chemiluminescence of EG and EGgwas strong and decreased rapidly, but was weak with ECgand negligible with EC. The structures of the radicals are proposed, and the relationship between the radicals and the chemiluminescence is discussed.