Antioxidant activity of cichoric acid and alkamides from Echinacea purpurea, alone and in combination

The antioxidant activity of extracts of the stems, leaves, and roots of Echinacea purpurea was compared with the antioxidant activity of purified cichoric acid and alkamides, both constituents of Echinacea purpurea. The antioxidant activity was determined using different methods: effect on oxygen consumption rate of a peroxidating lipid emulsion, and scavenging of radicals, i.e. 2,2-diphenyl-1-picrylhydrazyl (DPPH), measured by two different techniques. The efficacy of the extracts in the reaction with DPPH correlated well with the amount of cichoric acid present in the various extracts. The alkamides alone showed no antioxidant activity in any of the tests. Alkamides present in the extract increased, however, the antioxidative effect of cichoric acid in the peroxidating lipid emulsion. The activity was further compared with that of rosmarinic acid, a well-characterised antioxidant, and the extracts as well as cichoric acid were found to be efficient scavengers of radicals with an activity comparable to that of rosmarinic acid. Cichoric acid was found to have a stoichiometric factor of 4.0 in scavenging DPPH and to react in a second-order reaction with DPPH with a rate constant of 40 l/mol/s at 25 °C in methanol.