SVII-5
ポストハーベストにおける鮮度保持を目指した
プラズマ殺菌技術の開発
Development of inactivation technology using plasma
for freshness-keeping on post-harvest management
太田貴之1，橋爪博司1，伊藤昌文1，竹田圭吾2，石川健治2，堀勝2
T. Ohta1, H. Hashizume1, M. Ito1, K. Takeda2, K. Ishikawa2, M. Hori2
1

名城大 理工，2名古屋大院 工1
Meijo University, 2Nagoya University
1. Introduction
In agricultural fields and plant protection
stations, pesticides are sprayed to protect crops
from various insects and viruses. Fungi, such as
Aspergillus or Penicillium, contaminate foods, suchas cereals, fruits, vegetables, meats. However,residual agricultural chemicals (e.g., thiabendazole,imazalil, and ortho-phenylphenol) are harmful tothe human body and the environment. Moreover,methyl bromide, which is the one of effectively
pesticides, is also sprayed to the crops. Methyl
bromide is an ozone depletion material and had
been forbidden to be used since 2005, based on"Montreal Protocol on Substances that Deplete theOzoneLayer".
However,theusefulsubstitute-technology has not been developed yet.
Conventional inactivation techniques are autoclaves,ovens, and chemicals such as ethylene oxide,hydrogen peroxide, etc. However, their chemicals
cause some harmful problems for the human bodyand environment due to its toxicity. In the cases ofautoclaves and ovens, the heat damages to crops
become a problem. The establishment of
substitute-technology has been required.
Recently,non-equilibrium
atmosphericpressure plasma (NEAPP) has been much attention
for applications in biology, medicine, agriculture
and so on. There are many reports thatmicroorganisms such as fungi, yeast, bacteria,
cancer cell, and so on, were inactivated using cold
plasmas. The cold plasma simultaneously produces
various factors, such as vacuum ultraviolet (VUV)
and UV-C emissions, neutral and charged species,and electric fields, which may synergistically affectto inactivate microorganisms. Several studies
suggested that reactive oxygen species (ROS) may
be the dominant factor on the inactivation of themicroorganisms by plasmas. The bactericidal effectof plasma differs depending on microorganisms
owing to the resistance against the bactericidal
factor. It is essential to study the resistance against
the bactericidal factor produced by the plasma

based on the quantitative diagnostics of the plasma.
We have focused on inactivating the spores ofPenicillium digitatum in gas phase. [1-6] The green
mold of citrus is caused by spores of P. digitatum.
Spores of P. digitatum, which is fungus, aredifferent from other microorganisms for medical
applications because of the resistant structure,composition, and function of their cell wall.
In this study, in order to develop theinactivation technology using plasmas with higheffectiveness for freshness-keeping on post-harvest
management, we quantitatively elucidated theinactivation mechanism of P. digitatum spore basedon the measurement of the number density ofradicals such as ground-state atomic oxygen[O(3Pj=0,1,2)], singlet oxygen molecule [O2(1Δg)] ,and ozone.
2. Experimental
Figure 1 shows a schematic diagram of theexperimental setup containing an oxygen-radicalsource employing a non-equilibrium atmosphericpressure O2/Ar plasma with a vacuum ultraviolet
absorption spectroscopy optical system. The radicalO2+Ar

High AC voltage

Ar purgelamp
MHCLO2/He

Height:10 mm

Radicalsource

VUV
Monochromator

MgF2 window

PMT

Absorption length: 6.5 mm
ExhaustExhaustExhaustFigure 1. schematic diagram of the experimental
setup containing an oxygen-radical source.

4. Summary
In order to investigate the effect of reactive
oxygen species on inactivation of P. digitatum
spores, we measured the radical densities of O(3Pj)
and O2(1Δg), both of which have high oxidation
reactivity, using VUV absorption spectroscopy.
Considering that the inactivation rate of P.
digitatum spores decreased as a function ofexposure distance, we elucidated that O(3Pj) is themain factor responsible for inactivation of P.
digitatum spores rather than O2(1Δg).
5. References[1]S. Iseki, T. Ohta, A. Aomatsu, M. Ito, H. Kano, Y.
Higashiyama and M. Hori: Appl. Phys. Lett., 96(2010) 153704.
[2]S. Iseki, H. Hashizume, F. Jia, K. Takeda, K.

Figure 2 the result of the inactivation of P. digitatum
spores on Citrus unshiu with or without the oxygen
radical treatment.
1E+161016

31000
10

1E+151015

210100

1E+141014

11010

1E+131013

1012
1E+1200

3P ) density
O(系列1j1O
系列22( Δg) density

D-value
系列355101520101520
Exposure distance (mm)D-value (min)3. Results
Figure 2 shows the result of the inactivation ofP. digitatum spores on Citrus unshiu with orwithout the oxygen radical treatment.
Figure 3 shows the relationship between
D-value and the results of O(3Pj) and O2(1Δg)
densities. O2(1Δg) density were constant from 10mm to 20 mm of exposure distances, while O(3Pj)
density decreased dependent on exposure distance.
These results indicates that the inactivation
efficiencies are related to O(3Pj) density rather thanthose of O2(1Δg). We suggested that O(3Pj) is themain factor in oxygen radicals to inactivate P.
digitatum spores and that O2(1Δg) is less effective.

Ishikawa, T. Ohta, M. Ito and M. Hori: Appl. Phys.
Express, 4 (2011) 116201.
[3]M. Ito and T. Ohta M. Hori: J. the Korean Phys.
Soc., 60, (2012) 937.
[4]H. Hashizume, T. Ohta, J. Fengdong, K. Takeda,K. Ishikawa, M. Hori, M. Ito: Appl. Phys. Lett., 103(2013) 153708.
[5]H. Hashizume, T. Ohta, T. Mori, S. Iseki, M.
Hori, and M. Ito: Jpn. J. Appl. Phys., 52 (2013)056202.
[6]K. Ishikawa, H. Mizuno, H. Tanaka, K. Tamiya,H. Hashizume, T. Ohta, M. Ito, S. Iseki, K. Takeda,
H. Kondo, M. Sekine, and M. Hori: Appl. Phys.
Lett., 101, (2012) 013704.
[7]M. Iwasaki, H. Inui, Y. Matsudaira, H. Kano, N.
Yoshida, M. Ito and M. Hori: Appl. Phys. Lett., 92(2008) 081503.
[8]H. Inui, K. Takeda, H. Kondo, K. Ishikawa, M.
Sekine, H. Kano, N. Yoshida and M. Hori: Appl.
Phys. Express, 3 (2010) 126101.

Radical density (cm-3)

source was developed based on the high-density
NEAPP, which generates high-density electrons ofabout 1016 cm-3.[7, 8] The charged species andoptical radiation from the plasma were blocked by
the exit aperture of the radical source, so thatsamples are exposed to only neutral species. The
chamber containing the radical source was purgedwith Ar gas to eliminate the influence of
atmospheric gases. Measurements and exposures ofradicals to spores were performed at 10 to 20 mm
downstream from the radical head. Flow rate ratioO2/(O2+Ar) was also varied from 0 to 1.2 % at total
flow rate of 5 slm.
The absolute densities of O(3Pj) and O2(1Δg)
were measured by VUVAS using a microdischarge
hollow-cathode lamp (MHCL) and a deutrium lamp,
respectively. VUV light from the light source
passed though the MgF2 window and wasintroduced into the chamber. VUV light passing
through the absorption region was focused on theslit of a VUV monochromator with the MgF2 lensand detected by a photomultiplier tube.

1010-1100.12525Figure 3 number densities of O(3Pj) and O2(1Δg), andD-value as a function of exposure distance.