2.4. EPR spectra of freeze-dried fruit samples
The free radical EPR signal from all of the freeze-dried
samples consist of a single peak with g = 2.0053 ± 0.0002
and line width 0.7804 ± 0.0347 mT. This latter value is
considerably smaller than that for the frozen samples. The
variations of the spectral intensities with time of harvest
(Fig. 7) show that droughting had a detectable influence on
the free radical contents of freeze-dried fruits of cv. Elsanta
and cv. Semperflorens, whereas there was no significant
difference between the stressed and control cv. Symphony
samples at each harvest.
The free radical contents in the freeze-dried samples
were an order of magnitude higher than those in the
equivalent frozen samples (expressed on a dry weight
basis). Thus, even a mild processing treatment such as
freeze-drying results in massive free radical production. The
free radical levels in the control samples of cv. Elsanta and
cv. Semperflorens showed a small but progressive decrease
with successive harvests (i.e. with increasing age of the
plants).With the stressed plants there was an increase in free
radical concentrations over the first three harvests, followed
by a decrease in the later stages of the experiment. With cv.
Symphony, the free radical contents of the stressed and
control samples were essentially identical at each harvest,
and the trends between harvests were similar to those of the
stressed samples from the other varieties.
When the free radical content of the freeze-dried fruit is
compared with the water content of the fresh fruit, there is
an approximately inverse linear relationship (Fig. 8). Thus,
the greatest level of free radical production on freeze-drying
occurs in the fruit with the lowest water content.