23P016-O
Treatment characteristics of amino acid and sterilization mechanism
Using RF oxygen plasma
高周波酸素プラズマによるアミノ酸の処理特性と滅菌機序の解明
Akari Nakahigashi1), Nobuya Hayashi1), Kouzou Kanda2) and Kazusato Ohshima2)
中東朱里1), 林 信哉1)，神田康三2)，大島一里2)
1)

Faculty of Science and Electronic Engineering, Saga University, 1, honjohmachi, sagashi 840-8502, Japan
佐賀大学工学系研究科 〒840-8502 佐賀市本庄町12)
Faculty of agriculture, Saga University, 1, honjohmachi, sagashi 840-8502, Japan
佐賀大学農学部 〒840-8502 佐賀市本庄町1

Spore of microorganism is quite resistant to heat, high pressure and chemical agent, and therefore its treatment isimportant. In order to investigate sterilization factors and mechanism of the plasma treatment for medical equipmentusing oxygen plasma, interaction between oxygen plasma and Bacillus subtilis var. Natto or metionine that is major
composition of spore coat is investigated.

1. Introduction
On medical equipment sterilization, treatment ofbacillus and virus attached surface of medical
equipment is significantly important. Since, spore
coat of Gram-positive bacteria contains amino acidabundantly, it is necessary to investigate thedecomposition characteristics of amino acid inspore bacillus for sterilization. It is difficult tosterilize spore coat, therefore conventional
sterilization uses heat, strong acid and radial ray,although those methods cannot be applied to nonheat-proof and non chemical-proof, materials [1].
Recent years, methods of sterilization of medical
equipment and foods are developed using plasma[2]. However, inactivation mechanism of bacillus

and virus using plasmas is not clarified yet. In thisstudy, metionine that is sulfur containing
proteinogenic amino acids located spore coat andBacillus subtilis var.natto are exposed to oxygen
plasma. The treatment characteristics of amino acidand the sterilization mechanism are determinedusing RF oxygen plasma.
2. Experimental apparatus
The chamber made of stainless is evacuated andoxygen gas is introduced at several Pa. The oxygen
plasma is produced using the RF CCP antenna. The
RF power is 60W and the treatment time is 2 h. The
samples to be treated are metionine and Bacillus

100
2000

777nm
844nm

1800

1400
1200
1000
800
600
400

7060
50
40302010200
080
Decomposition rate (%)

Intensity (arb.units)

1600

C-HS-CH3
amid 190204060Pressure (Pa)

80

100

Fig.1 Dependency of light emission intensityfrom oxygen radicals on the gas pressure.

00

204060Pressure (Pa)

80

100

Fig.2 Decomposition rate of major bonds ofmetionine varying the pressure.

BeforeAfter

1.6amid I

C-H

BeforeAfter

1.8

Absorbance (arb.units)

Absobance (arb.units)

2.0

2.4
2.2
2.0
1.8
1.6
1.4
1.2
1.0
0.8
0.6
0.4
0.2
0.0
-0.2

S-CH3

amid I

1.4
1.2

C-H

1.0
0.8

S-CH3

0.6
0.4
0.2
0.012001250

13001350

14001450

1500-1

Wavenumber (cm )Fig.3 FTIR spectra of plasma treatment
Bacillus subtilis var. natto at the pressureof 20Pa.

subtilis var. natto. These materials are put on CaF2
plate and dried completely, and set on the center ofchamber and exposed to oxygen plasma. The
density of metionine and Bacillus subtilis var. natto
is 19mg/cm2 const and distance of sample to CCP
antenna is 6cm [2]. After treatment, these samples
are measured FTIR spectroscopy.
3. Result and discussion
3.1 Treatment of metionine
Figure2 shows decomposition rate of metionine
estimated from major peak in FTIR spectra ofsample before and after the plasma irradiation. At
the pressure of 20Pa, C-H bond (at 951cm-1) isdecomposed 70% at maximum, and decomposition
rates of S-CH3 bond (at 1316cm-1) and amidⅠ(at1617cm-1) was 46%, 45% respectively.
While, at the pressure of 100Pa, the decomposition
rates of C-H bonds and S-CH3 bonds are lower thanthose of 20Pa, 60Pa, and decomposition rate ofamid I is larger at 60Pa than 20Pa. Furthermore, it
is obvious that oxygen radicals dissociate andcombine to another bond and produces sulfur oxide(SOx), like a sulfo acid and cisteine acid at
1045cm-1, 1149cm-1 and 1183cm-1 a maximum at
100Pa. Moreover, the decomposition rate of amid
Ⅰat the pressure of 60Pa is the lowest, 30% and of
C-H bonds, S-CH3 bonds are 47%, 34%
respectively.
3.2 Treatment of Bacillus subtilis var. natto
Figure3 shows Bacillus subtilis var. natto exposed
oxygen plasma at the pressure of 20Pa. Major peakC-H bonds (at 1250cm-1), S-CH3 bonds-0.2
12001250

1300135014001450

1500-1

Wavenumber (cm )Fig.4 FTIR spectra of plasma treatment
Bacillus subtilis var. natto at the pressureof 100Pa.

(at1275cm-1) and amid I (at 1443cm-1) cannot
dissociate at the pressure of 20Pa. Figure4 shows
the sample of Bacillus subtilis var. natto at thepressure of 100Pa. Major peak of C-H bonds,
S-CH3 bonds and NH bonds. Those decomposition
rates are 41%, 31% and 28%, respectively.
On the treatment of Bacillus subtilis var. natto,
surface on its spore coats would be laked by oxygenions and radicals. Then spore coats lost the function
ofspore.
Therefore,decomposition
ofsulfur-containing proteinogenic amino acids are oneof the candidates of spore inactivation.
4. Conclusion
Decomposition characteristics of amino acid andbacillus spore are studied using the RF oxygen
plasma, and sterilization mechanism of spore isinvestigated.
・Metionine is decomposed 70% (C-H bonds), 46%(S-CH3 bonds) and 45% (amid I) at the pressureof 20Pa and generated sulfur oxide at 100Pa. At
100Pa decomposition rate of C-H bonds, S-CH3bons and amid I are 28%, 12% and 34%,respectively.
・Bacillus subtilis var. natto is decomposed 41%(C-H bonds), 30% (S-CH3 bonds) and 28% (amidI), each at the pressure of 100Pa. Oxygen ionsetch on the surface of bacillus on the CaF2 plate.
References[1] N. Hayashi, W. Guan, S. Tsutsui, T. Tomari and Y.
Hanada: J. J. Appl. Phys. 45 (2006) 8358-8363.
[2] N. Hayashi, A. Nakahigashi, H. Riu and M.
Goto: J. J. Appl. Phys. 49 (2010) 08JH02