Quantum Beam Science Research

5-14 Which Liver-Sashimi was Treated by Radiation?
ᴪ Development of a Method to Distinguish Disinfected Liver ᴪγ-irradiated raw bovine livers

Inserting livers
into ESR tubes

Freezing inliquid nitrogen

ESR measurements
in liquid nitrogen

Fig.5-35 Schematic of electron spin resonance (ESR) measurements
Raw bovine livers were irradiated with 1.0, 2.6, 5.2, and 7.8 kGy γ-rays at 0 °C. The irradiated samples were inserted
into ESR tubes, frozen at −196 °C with liquid nitrogen, and measured on an ESR at their frozen temperature.

Side peak intensities (a.u.)

250

0 kGy
1.0 kGy
2.6 kGy
5.2 kGy
7.8 kGy

Right side peak0
Left side peak−2048300⎧⎨⎩

Signal intensities (a.u.)

2048

Main peak

200

Right side peak

150
100
50

Left side peak

0310

320
330
340
Magnetic field (mT)

350

360

02
46Absorbed dose (kGy)8

Fig.5-36 Changes of ESR spectra of irradiated raw bovine livers
ESR spectra of raw bovine livers irradiated with different doses
are depicted on this plot. Arrows indicate the dose-responsiblepeaks after irradiation. A large peak in the center is called themain peak, and the two small peaks to the left and right of themain peak are called side peaks.

Fig.5-37 Dose responses of side peaks on bovine
livers
The intensities of the right and left side peaks wereplotted against absorbed doses. The peak intensities on
the plot increased linearly according to increasing doseat each different slope.

To prevent foodborne illness in Japan, after the outside ofraw meat had been roasted and then the cooked parts were
trimmed off, the steak tartare must be prepared from only theinside meat in restaurants. However, since pathogenic bacteriasuch as some E. coli were found inside raw bovine livers
where no disinfection method is effective, the sale of any
raw bovine liver to eat as “liver-sashimi” has been prohibitedsince July 1, 2012. Providing for the radiation exposure that isused to sterilize bacteria out of a sealed food package without
heating, detection methods have been developed to distinguish
raw livers that have been disinfected by radiation.
At ﬁrst, the irradiated raw bovine livers were subjected to theELISA method, which was developed as for irradiated groundmeats. The ELISA method could distinguish irradiated livers
when such irradiation was done in the chilled condition (0 °C),
but not at all could be detected when irradiation was done in thefrozen condition (‒80 °C).
The ELISA method can detect an oxidative lesion in DNA thatreacts with active species (radicals) caused by ionizing radiation.
Therefore, the radical migration to DNA might be inhibited inthe frozen condition. Next, we tried to detect the radical itself.
Basically, unpaired electrons of radicals can be measured using
electron spin resonance (ESR) spectroscopy. This apparatus

utilizes an electromagnetic wave similar to a microwave oven.
Therefore, the method has a weak point in that the electron
cannot resonate when the water within the samples absorbs
the microwave. However, we have demonstrated that ESR
can measure radicals in the flesh of fresh fruits irradiated as adisinfestation treatment for the plant quarantine. Thus, we thoughtthat it might be possible to measure radicals in livers using ESR.
After raw bovine livers were irradiated in the chilledcondition, they were measured at liquid-nitrogen temperature
to suppress microwave absorption by stopping the motionof the water molecules during ESR measurement (Fig.5-35).
According to the results, we found a main peak and two side
peaks in the livers (Fig.5-36), and the side-peak intensities
increased according to the increasing doses (Fig.5-37). Since
the measuring errors were involved in experimental values, weassumed that the side-peak intensities of the raw bovine livers
irradiated at approximately 3 kGy could be clearly distinguishedfrom those that were not irradiated. Therefore, it is suggested
that raw bovine liver treated by irradiation beyond 3 kGy can be
distinguished using the ESR method.
Since the ESR method can be used to investigate the raw
bovine livers being irradiated for disinfection, we believe that thistechnique can help consumers to choose reliable liver-sashimi.

Reference
Kikuchi, M. et al., ESR Signal Changes Recorded in γ-Irradiated Bovine Livers, Shokuhin Shosha (Food Irradiation, Japan), vol.50, no.1, 2015, p.9-12(in Japanese).

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JAEA R&D Review 2016-17