2.3. EPR spectra of 4-POBN adducts from cv.
Semperflorens samples
In order to investigate the generation of unstable radicals,
frozen samples of Fragaria vesca cv. Semperflorens were
treated with solutions of the spin trap 4-POBN. This spin
trap is able to react with unstable free radicals to form an
adduct, which is itself a free radical. Radical adducts
generally have much greater stability than the parent radicals,
and additionally their spectral parameters vary with the
chemical nature of the trapped radical. A typical EPR
spectrum of a 4-POBN adduct obtained with strawberry
fruit is shown in Fig. 5. It consists of six peaks as a result of
interaction of the unpaired electron with the 14N (I = 1) of
the nitroxide and the 1H (I = ½) on the α-carbon. The
hyperfine coupling constants are a(1H) = 0.290 mT and
a(14N) = 1.550 mT, which are consistent with the trapped
radical being a •C-centred species [5]. The spectral intensities
(Fig. 6) show no significant differences between any of
the samples. There is thus no influence of droughting or
plant age on the levels of unstable free radicals that can be
trapped from these crushed frozen samples.