22G07
Chemical reaction of unsaturated fatty acidinduced by atmospheric-pressure plasma
大気圧低温プラズマを照射した不飽和脂肪酸の反応について
Satoshi Fukui１, Atsushi Tani１, Satoshi Ikawa2 and Katsuhisa Kitano3
福井	  智1, 谷	  篤史1，井川	  聡2，北野	  勝久3１

Department of Earth and Space Science, Graduate School of Science, Osaka University
1-1 Machikaneyama, Toyonaka, Osaka 560-0043, Japan
大阪大学大学院理学研究科宇宙地球科学専攻	  〒560-0043	  大阪府豊中市待兼山1-1
2
Technology Research Institute of Osaka Prefecture
2-7-1 Ayumino, Izumi, Osaka 594-1157, Japan
大阪府立産業技術総合研究所	  〒594-1157	  大阪府和泉市あゆみ野 2-7-1
3
Center for atomic and Molecular Technologies, Graduate School of Engineering, Osaka University
2-1 Yamadaoka, Suita, Osaka 565-0871, Japan
大阪大学大学院工学研究科原子分子イオン制御理工学センター	  〒565-0871	  大阪府吹田市山田丘 2-1
Atmospheric-pressure plasma has been used for attractive applications, for example, in sterilization andpolymerization, but the effect of the plasma on organic materials is not clear enough. We have investigatedoxidation reaction of linoleic acid, one of unsaturated fatty acids by the atmospheric-pressure plasma jet.
Formation of malondialdehyde (MDA) through oxidation of linoleic acid was observed in helium andoxygen mixed atmosphere. We suppose that some active oxygen species produced by the plasma jet
oxidize unsaturated fatty acid if oxygen is included in atmosphere.

1. Introduction
Recently, technologies of atmospheric-pressure
nonthermal plasma have been developed intensively
and its applications attract remarkable attention.
Atmospheric-pressureplasmacanproduce
valuable chemically active species, and this typeof plasma is desirably applied to soft materials
like polymeric biomaterial and human body as
medical device [1].
It is required to clarify the effect of
atmospheric-pressure plasma on organic materials.
In this study, we focus on lipid as one ofbiomacromolecules. Unsaturated fatty acid in
lipid is oxidized to lipid peroxide by some oxidant
stress. After successive decomposition reactions oflipid peroxide, malondialdehyde (MDA) is formed.
Ohkawa et al. reported that thiobarbituric acid(TBA) reacted with MDA and produced redpigment [2]. The amount of red pigment, i.e. opticalabsorbance at 532 nm is an indicator of oxidation
degree of unsaturated fatty acid.
In this experiment, the plasma jet was exposed tolinoleic acid, one of unsaturated fatty acids in theatmospheric-controlled chamber to investigate
oxidation reaction by TBA tests.
2. Experimental Setup and Methods
A schematic view and a photograph of theplasma jet and the chamber are shown in Fig. 1. A
glass tube on the top of the chamber was used forHea)

Glass tubeb)

Electrode
10 kV
ExhaustO2

ExhaustExhaustPlasmaGlass
Lipid
GroundFig. 1 A schematic view (a) and a photograph (b)of the atmospheric-pressure plasma jet and thechamber. Gas flows are indicated with red arrows
for He + O2 mixed atmosphere and blue arrows forpure He atmosphere.

a supply of helium gas. Two ambient gases in thechamber were tested. In helium and oxygen
mixed (He + O 2) atmosphere, oxygen gas wassupplied from the side port of the chamber andthe other port was used for exhaust, as shownwith red arrows in Fig. 1-a. In pure helium
atmosphere, both side ports were used for exhaust(blue arrows in Fig. 1-a). The flow rates were
controlled with mass flow controllers (KOFLOC,8500MC); 3 L/min for helium and 0.5 L/min foroxygen.
The chamber was composed of a glass cup
sealed by O-ring. After purging the ambient gas

3. Results and Discussion
Absorbance spectra of the red pigment in thelinoleic acid exposed by the plasma jet in heliumand oxygen mixed (He + O2) atmosphere increase
with the exposure time of the plasma in Fig. 2. As
shown in Fig. 3, absorbance at 532 nm changes
with the exposure time in the plasma with andwithout O2 mixture. According to literature [2],oxidation degree is evaluated from absorbance at532 nm. In Fig. 3, absorbance at 532 nm in He + O2atmosphere increased with the exposure time, while
there was little change in absorbance in pure Heatmosphere.
Since the plasma jet oxidizes unsaturated fatty
acid and produces MDA in He + O2 atmosphere,
but the plasma jet does not oxidize unsaturated fatty
acid in pure He atmosphere, unsaturated fatty acidis oxidized effectively by some active oxygen
species with the plasma jet exposure. Therefore, it
is supposed that lipid which is mainly consisted of
unsaturated fatty acid should be oxidized by theplasma jet if oxygen is included in atmosphere.
4. Conclusion
Investigation on the oxidation reaction of linoleic

1.4
without plasma
with 10 min plasma
with 20 min plasma
with 30 min plasma

1.2

Absorbance

10.8
0.6
0.40.20450500

550600wave length (nm)650700Fig. 2 Absorbance spectra of red pigment produced byreaction of the linoleic acid samples with TBA. The linoleic
acid was exposed by the atmospheric-pressure plasma jet inhelium and oxygen mixed (He + O2) atmosphere.
1.4
He
He + O22

1.2
Absorbance at 532 nm

in the chamber with the gas flows for 3 min, theplasma jet was exposed to 500 µL of linoleic acidin the cup. High voltage (~10 kV) with low
frequency (~10 kHz) was applied to thesingle-sided electrode [3].
In preparation of TBA test, the following fivesolutions were mixed with 50.0 µL of eachlinoleic acid sample; (1) 400 µL of 2 mM
ethylenediaminetetraacetic acid (EDTA) aqueoussolution, (2) 100 µL of 8.1% sodium dodecyl
sulfate (SDS) aqueous solution, (3) 750 µL of0.1 M acetic acid solution, (4) 750 µL of 0.8%
TBA aqueous solution, and (5) 25.0 µL of 0.8%
dibutylhydroxytoluene (BHT) acetic acid solution.
The mixed solutions were heated at 95˚C for
60 min and cooled with ice. After 500 µL ofwater and 2.50 mL of n-butanol:pyridine (15:1,v/v) were added to the solutions, they werecentrifuged at 3000 rpm for 10 min. The organic
phase extracted from the solutions was measured
with UV-VIS spectrophotometer (JASCO, V-630).
In oxidation of unsaturated fatty acid, not only
MDA but also other aldehydes are released. Otheraldehydes have an influence on TBA tests because
the reaction is promoted with a small amount ofiron ions [4]. EDTA solution inhibits the reaction
aldehydes with TBA, so EDTA was used in thisstudy to evaluate the amount of MDA, i.e. toinvestigate oxidation degree of linoleic acid.

10.8
0.6
0.4
0.2
005

1015

202530Plasma exposure time (min)Fig.3 Changes of absorbance at 532 nm in theexposure time of the plasma jet (n = 3).

acid exposed by the plasma jet indicates thatoxidation reaction is promoted in unsaturated fatty
acid with active oxygen species by plasma-induced
chemical reaction in liquid if oxygen is in ambient
atmosphere.
Finally, affect of plasma irradiation to human forhemostasis, disinfection, wound healing etc. in theresearch area of plasma medicine should be
evaluated for the optimization of positive effect andthe safety of negative effect. It is important subject
to figure out the reaction of plasmas tobiomolecules considering plasma-induced chemical
processing in solution.
Reference[1] 北野勝久、現代化学，7 月号，25，(2009).
[2] H. Ohkawa et al, J. Lipid Res., 19, 1053-1058, (1978)[3] 北野勝久、応用物理学会誌，77(4)， 383，(2008)[4] H. Kosugi et al, J. Am. Oil Chem. Soc., 68, 51-55.
(1991)