Cichoric acid (2R,3R-O-dicaffeoyltartaric acid) (1) is highly susceptible t
o enzymatic degradation during the preparation of Echinacea purpurea produc
ts. Degradation of 1 and other caffeic acid derivatives can be inhibited by
antioxidants added to the extraction solvent or in buffered protein extrac
ts saturated with nitrogen. Inhibitor studies conducted with protein extrac
ts prepared from dried overground parts of E. purpurea revealed that polyph
enol oxidases (PPO) but not peroxidases are responsible for the oxidative d
egradation of exogenous and endogenous caffeic acid derivatives. With a vie
w to stabilizing aqueous extracts with respect to their content of 1, the e
ffects of ascorbic acid and ethanol were tested. Compound 1 was not stable
under conditions where oxidative processes could almost be excluded. It was
found that an esterase hydrolyzing the ester bonds between tartaric acid a
nd caffeic acid is still active under PPO inhibitory conditions. Finally, a
ddition of 40% ethanol and 50 mM ascorbic acid to aqueous extracts of "Echi
naceae purpureae herba" resulted in a constant amount of cichoric acid over
four weeks.