01Bp01
時空間制御された電場・プラズマ場での水・タンパク質・生体の状態変化
Property Change of Biological Components (Water, Protein and Living
Organisms) in Temporally and Spatially Controlled Electric Field and Plasma
高木浩一1,2)
TAKAKI Koichi1,2)
1)

岩手大学，2)次世代アグリイノベーション研究センター
1)
Iwate University, 2)Agri-Innovation Center

1. Introduction
In bio-applications of pulsed power, the novel
control of plasma and intense pulsed electric field(PEF) with spatially and temporally is important toadapt whole bio-scale as shown in Fig. 1. Especially,
the nano- or sub-nanoseconds pulse is required tosatisfy the limit of relaxation or charging time ofwater molecule and protein. The pulsed power
generator is designed to match temporally changed
impedance of bio-specimen by choosing optimum
system (pulse forming line, H-bridge circuit,inductive and capacitive energy storage circuit) andsemiconductor switches such as SiC-FET [1, 2]. In
this article, the effect of applying voltage and plasma
on property of biological components such as water,protein and living organisms is described.
従来型
従来型
新型
新型

21.510150.500-5-0.5-10-100102030

Plant
Food...

Tissue,cell...

Pulsed power

<1 nm
H

0.38nmCellmemblane
Voltage[kV]

Protein,enzyme...

Cellularchemical
reaction3

Voltage2

Current

AminoacidO
Water
molecule
<1ns

<1μs

<10μs>10μs

Ultra-HS
PFL

nanoS
IES

microS
CES

High-rep
SiC-FETH

10-10𝐽0 exp

𝑅

Conventional-1
40Time, ns<20nm

where, r is the freezing speed [℃/s] ， ni is thenucleation number for each temperature band, and∆Ti is the band width of temperature (=1 K).
The nucleation rate increase with increasing acEFfrequency. The nuclation rate R is expressed using
Arrhenius equation as follows;

12Time [s]3502. Water Nucleation in AC Electric Field
A water nucleation is the process in freezingwater containing materials such as gel-type foods,
vegetables, meets and fishes. Recently, the freezing
process with applying an AC electric field (acEF) istrying to be utilized in some companies forcontrolling ice nucleation in the freezing process.
Figure 2 shows ice nucleation rate of distilledwater for different frequencies of acEF [3]. The(2),/-2

Relaxation timeFig. 1 Relation between bio-scale and relaxation (orcharging) time required as pulsed power specification.

∆𝐺∗kB 𝑇

where, J0 is the frequency factor, ∆G* is theactivation energy, and kB is Boltzmann constant.
Figure 2 shows that the slope of the lines is
independent of acEF frequency and the nucleation
rate shifts in parallel with increasing the frequency.
The result indicates that the acEF mainly affects thenucleation frequency factor J0.

Log10R<10μmOutput Voltage, kV>1mm15Output Current, kA

Bio scale (molecular size)

20distilled water is used as samples, and is placed
between the parallel plate electrodes in a freezer. Thetemperature inside the freezer is fixed at -15 ℃. The
sinusoidal wave voltage is applied to the electrode togenerate acEF. The acEF strength is fixed at 50 kV/m.
A thermistor is used to measure the temperature. Theice nucleation rate R is obtained using the equation;𝑟𝑛𝑅 𝑇𝑛(1),∑ 𝑛∆𝑇
2-3-4-1050 Hz
500 Hz1 kHzControl-8-6-4-2
Temperature [°C]0Fig. 2 Nucleation rate of distilled water for different
frequencies at 50 kV/m applied electric field.

increasing strength of electric field at same input
energy. This result indicates that the strength ofelectric field strongly affects the efficiency of protein
conformational change, resulting in enzyme
inactivation.
4. Pulsed Electric Stimulation for Fruiting
The pulsed high-voltage can be used as
stimulation for fruiting promotion. The mushroom
fruiting bodies are also promoted by the pulsed
voltage application as electrical stimulation. The
basically process is as follows; the mushroom
hyphae are accelerated with Coulomb force owing tothe strong electrical field. As the result, some hyphae
are scratched and cut by the movement. Thesehyphae cutting or scratching are worked as trigger totransfer from vegetative growth to reproduction
growth. This process can be confirmed using
metabolism analysis. Figure 5 shows the hyphae
activity analysis using hydrophobin release, which ismainly observed before the fruit body formation innature [5]. The hydrophobin release decreases forthree hours after stimulation. However, thehydrophobin release from the vegetative hyphae
increases 2.3 times one day after the stimulation.
70

Hyd2 release

3. Conformational Change of Protein
Enzymes are large-size proteins which works as
biological catalysts. The enzymes are frequently
utilized in food industry such as fermentation in
brewing process and making dairy products. Pulsed
electric field (PEF) technology is a basically nonthermal food treatment method that involves the useof short electricity pulses for microbial andenzymatic inactivation through the protein
conformational change.
Figure 3 shows the residual activity of-amylasefor various electric field strengths at same input
energy of 720 J [4]. The residual activity ofamylase decreases with increasing strength ofelectric field at same input energy. The strength ofelectric field is strongly related to efficiency ofprotein conformational change. Therefore, thestrength of electric field is dominant parameter in
PEF treatment for enzyme inactivation.
Figure 4 shows the tertiary structure change by
PEF treatment [4]. The fluorescence spectra of amylase at 280 nm wavelength of excitation light isused to monitor the tertiary structure change forvarious strength of pulsed electric field at same inputenergy of 720 J. The tertiary structure (mainlytryptophan) of-amylase also decreases with60

outside50inside403020100
control3 hours 1 day 2 days 3 days 7 days
Days after pulse electric field stimulation

Fig. 3 Residual activity of-amylase as a function ofelectric field strength at same input energy of 720 J.
6000

Intensity

5000
4000

Control
5 kV/cm
12.5 kV/cm

3000
2000

Acknowledgments
This work was supported by Grant-in-Aid
Scientific Research (S) Grant: 19H05611.
References

1000
0Fig. 5 Hydrophobin release for various periods after100 kV pulsed high-voltage stimulation at two different
parts of the hyphae. The label “outside” indicates
actively cell separation (vegetative) hyphae and the“inside” is inactive hyphae.

300400
Wavelength [nm]Fig. 4 Fluorescence spectra of amylase at 280 nm
wavelength of excitation light emission after PEF
treatment for various PEF strength at 720 J input energy.

[1] K. Takaki et al., J. Phys. D: Appl. Phys. 52, 473001(2019).
[2] K. Takahashi et al., IEEJ Trans. FM. 139, 413 (2019).
[3] K. Kaga et al., Proc. IEEJ FM Conf., 3-B-a2-5 (2019).
[4] K. Takahashi et al., Int. J. Plasma Environ. Sci.
Technol. (in submission).
[5] K. Takaki et al., Microorganisms, 2, 58 (2014).