M. Geoffroy et al., RADICAL INTERMEDIATES AND ANTIOXIDANTS - AN ESR STUDY OF RADICALS FORMED ON CARNOSIC ACID IN THE PRESENCE OF OXIDIZED LIPIDS, Free radical research, 21(4), 1994, pp. 247-258
Carnosic acid, an antioxidant extracted from rosemary, is shown to pro
duce radicals when in contact with oxidized methyl oleate in the absen
ce of air above 50 degrees C. Two radical species are formed: the firs
t one, stable up to similar to 110 degrees C, is an hydroxy-phenoxy ra
dical whose ESR spectrum was analyzed by studying its temperature depe
ndence and its sensitivity to deuterium/proton exchange. The second sp
ecies was observed above 110 degrees C, its ESR spectrum was identical
to the spectrum obtained when carnosol, another antioxidant extracted
from rosemary, was heated at the same temperature in the presence of
oxidized lipid. This observation is probably due to the transformation
of carnosic acid into carnosol; the analysis of the corresponding ESR
spectrum suggests the formation of a keto phenoxy radical exhibiting
a great delocalization of the unpaired electron.