The generation of free radicals by cell disruption in different biological materials was investigated in the presence of spin traps by Electron Paramagnetic Resonance (EPR). Pro-oxidative activity of carrot and herb samples was observed with the spin traps PBN and 4-POBN.
Carbon-centred radicals were detected with DMPO derivatives, TRAZON and PEPO, .OH radicals were also trapped with DEPMPO and DPPMPO as spin traps. Specific identification of the free radical from mushroom as the N-t-butylhydronitroxide radical was possible with this range of spin traps. Oxidation of four specific phenolic compounds (kaempferol, luteolin, rosmarinic acid, carnosic acid) under different conditions resulted in different EPR spectra which were interpreted. Various structural suggestions have been formulated. The chosen oxidation conditions were relatively mild but all components could be easily oxidised, consistent with their excellent abilities to scavenge free radicals by donating hydrogen atoms. The stability of the detected radicals was quite long with at least 6 min. lifetime. The structures of kaempferol and CA changed by oxidation and their metabolites may be of relevance in the antioxidant mechanism. In contrast, the structures of RA and luteolin remained intact, and they are likely to be able to be redox-cycled. Information gained in this work could serve as basis for further investigations of food preparation or even the chewing process.
Furthermore the radical formation of relevant phenolic compounds was detected under physiologically relevant conditions at pH 7 and the formation of stable free radicals may be relevant to questions relating to their use as health products or pro-oxidative and toxic substances.