JAEA-Review-2010-065.pdf:15.99MB - 日本原子力研究開発機構

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Dose-dependency of Electron Spin Relaxations in
Irradiated Fresh Mangoes
M. Kikuchi a) , T. Sakashita a) , T. Funayama a) , M. Ukai b) ,
Y. Shimoyama c) and Y. Kobayashi a)
a) Radiation-Applied Biology Division, QuBS, JAEA, b) Hokkaido University of Education,
c) Muroran Institute of Technology
The irradiation to tropical fruits is used as a quarantine
treatment against fruit flies in the world. Distinguishing
the irradiation is required to endorse the reliability of labels
for consumers. Recently, we have found that the
radiation-induced radicals remain in irradiated fresh
mangoes 9 days after the irradiation 1) . Since lifetime of
radicals is related to where unpaired electrons are in the
surroundings, interactions of the unpaired electrons are
investigated for rough water-rich environments.
To measure ESR spectra of irradiated fresh mangoes, we
employed the freeze-dry method, a gentle treatment for the
biological samples. ESR spectroscopy was performed
with an RE-3X (Jeol) at room temperature using the X-band
microwave frequency (9.44 GHz). To estimate interaction
of the electrons, the relaxation times of T 1 and T 2 were
evaluated by a program code developed by Lund, et al. 2) .
Figure 1 shows progressive saturation behaviors (PSB)
for the main peak of dried specimens prepared from
irradiated water-rich mango fleshes at various microwave
powers. The PSB hits the maximum in the vicinity of
3 mW. The g-value (g = 2.004) and the PSB of the mango
specimens indicated a signal consisted of organic free
radicals.
The relationships between the relaxation times and the
irradiation doses are observed (Fig. 2). Generally,
relaxation time T 1 relates to the energy transfer through the
chemical bonds by the interactions between the electron
spin and the lattice. The relaxation time T2 relates the
interaction between the spins. Therefore, no difference
between irradiated and non-irradiated samples for T 1 values
indicates the existence of the energy transfer pathways
through chemical bonds. Dose-dependency of T 2 in flesh
and skin indicates that longer T2 is induced by weaker
interactions. This interaction should be related to the
inter-electron distance. Moreover, these responses may be
affected by the different water contents in the mango organs,
since torsional motion of biopolymers is easy in the
water-rich surroundings. Therefore, conformational
changes of some biopolymers with radicals were occurred
in the water-rich fruit after the increase of flexibility by
chemical bond breaks (Fig. 3). In seed that is of a
semi-dried, the increase of unpaired electron contents after
-irradiation causes stronger interactions, leading to shorter
T 2.
ESR spectroscopy on freeze-dried powdered specimens
of irradiated fresh mangoes can measure whole radicals
including both mechano-radicals and -induced radicals.
Additional relaxation time analyses might be possible to
JAEA-Review 2010-065
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distinguish the contribution of ESR signals by
radiation-induced radicals from that by whole radicals.
Finding of stable radicals in fresh fruits enables one to
know -induced radicals with novel methodology of T2 3)
dose-dependency .
References
1) M. Kikuchi et al., Spectrochim. Acta A 75 (2010)
310-313.
2) A. Lund et al., Radiat. Res. 172 (2009) 753-760.
3) M. Kikuchi et al., Food Irradiat. Jpn. 44 (2009) 9-13.
T 1 ( s)
140
120
100
80
60
40
40
20
(S)
(K)
(F)
20
0
0 10 20 30 40 50
0
60
Dose (kGy)
Fig. 2 Dose dependency of relaxation times for
irradiated mango fleshes (F), skins (S) and seeds (K).
Dotted and solid lines were fitted by the least square
method using T 1 and T 2 values, respectively.
O
H
20000
15000
10000
5000
CH 2OH
HO
H
H
H
O
OH
H
H
O
H
H
HO
CH 2OH
O
HO
H
O
H
H
0 kGy
4 kGy
12 kGy
25 kGy
50 kGy
0
0.0 2.0 4.0 6.0 8.0
Fig. 1 Progressive saturation curves of freeze-dry
specimens prepared from irradiated mango fleshes.
(F)
(S)
(K)
CH 2OH
HO
H
H
Fig. 3 A model as for a spin-spin interaction in the
cellulose biradical. Black dot corresponds an
unpaired electron in free radical.
140
120
100
80
60
H
O
OH
T 2 (ns)
H