S8-4
高電場プラズマを用いた生鮮植物の長期保存
Prolonged Preservation of Fresh Plants using High Electric Field Plasma
西田 靖 1,3)，劉沖明 2)，岩﨑憲一 3)
Y. Nishida1,3), C.M. Liu2) and K. Iwasaki3)
1)
1)
2)

成功大プラズマ研, 2)龍華科技大化工, 大高商事（株）
3)

Institute of Space and Plasma Sciences, National Cheng Kung University, Taiwan

Department of Chemical and Material Engineering, Lunghwa University of Science and Technology, Taiwan
3)

Daiko-Shoji Co. Ltd.

Abstract: “High Electric-Field Plasma (HEFP)” technique inexample. In this situation new serious problems havean atmospheric pressure has been developed to control andtaken place so far, such as change of color of crops, andkeep the environmental atmosphere in clean state; such as

poisonous for human body. When UV light is employedsterilization, much longer sustenance of fresh states of suchinstead of discharge system, same kinds of problems haveplants as vegetables, fruits and flowers, and deodorization ofarisen such as color change of the stored materials, ozone

atmospheric air. Here the HEFP system means that there areproduction and seriously harmful to the human body with

no apparent discharges between electrodes and the electric

direct irradiation, in addition to the quite low energy

field inside the system is as high as 3  4  10 V/m in theconversion efficiency from electricity to the UV light.

6atmospheric pressure. This high field plasma can decompose

We have developed new technique [1] named “Highharmful or poisonous materials for the fresh plants. This also

Electric-Field Plasma (HEFP)” system shown in Fig.1. In

kills bacteria. We have developed special refrigerator which

this system no apparent discharges such as corona or

has precise controlling system of temperature and humidity,

silent discharges within the electrodes appear, and theequipped with HEFP system. In the new refrigerator, usage

electric fields between electrodes keep as high enough asof harmful or poisonous materials such as ozone, OH

3  4  10 6 V/m in the atmosphere pressure. In the present

radicals or UV light are suppressed. In this refrigerator thefresh plants are preserved much longer duration without
increasing bacteria or mold on their surface, compared withconventional method employed so far.

1. Introduction
In the contemporary world many of the living life isfaced

toenvironmental

hazardous

circumstances,including air pollution, increasing CO 2 concentration,water pollution or stain and many others. For human life,
it is important issues to supply the fresh foods stably.
Therefore, it is necessary to develop preservation systemof fresh plants for a long duration without consuming
much energy. The plasma phenomena are employed as
one of the possible tools for solving these problems.
For decomposing and sterilization of toxic gases using
electrical discharges in atmospheric pressure harmful
ozone are generated if corona discharge is employed, forFig.1. Typical example of I-V characteristic in the discharge
system. The definition of HEFP area corresponds to “B-D”
area in the “Townsend regime”.

technique, pulsed high voltages with sharp rise time areapplied to the controlling electrodes and quite small
amount of current less than about 50 μA flows with apresent system, but no apparent discharges occur. In thissystem ozone generation was suppressed as small amountas possible, almost no production, and UV lightgeneration is also suppressed. Thus, apparent effects fromozone or UV light did not appear. This technique isunder well controlled conditions in temperature and humidity.

applicable for decomposing harmful or poisonous

The temperature can be adjusted within 1C accuracy and thechemical materials for the fresh plants and also for killing

humidity is 5 % to the set values. The high field system is set

bacteria or mold in the air. Therefore, this technique has

insideability to be applied for the contaminated gas cleaning

circulating duct. Insystems.

order to monitor

It is popularly known that plants are breathing to put

theairthe ethylene gas

off the ethylene gas even if they are taken out from thecontents

inthetrees or from the farming ground. As ethylene gas has

refrigerator, a probe

strong ripe effects on the fresh plants including

for ethylene gas

vegetables, fruits and flowers, it is necessary to remove

detector is inserted.

ethylene gas from the preservation spots in order to keep

When the plastic

Fig.2. Advanced Refrigerator equippedwith High-Electric Field Plasma generator
and humidifiercrops in fresh conditions for a long duration. Furthermore,boxes are used, these boxes are left in the experimental room

for a long preservation of the fresh plants, thewith room temperature of about 24 - 25 C through thesurrounding temperature and humidity are also anotherexperimental duration. The sizes of the boxes are 68 (W) cm x 49

key factors and well controlled system of these(D) cm x 39 (H) cm, and the top of the box is covered and tightly

parameters is required.

sealed while the experiments are undertaken. Therefore, ethylene

The

presentstudy

includescarbonhydrategas amount and humidity within each box are kept as they

decomposition for long preservation of fresh plants andare. In one box, only sample bananas on a weight scale were set,sterilization of bacteria in the surrounding area or on the

but in other boxes the HEFP system in addition to sample

surface of the plants, by using high field plasma systembananas on a scale were sealed together. Here, one of the highequipped in a special refrigerator. This refrigerator has

field systems was home-made, but the other one was made byshown quite effective results to keep fresh plants as theyIDX Co. in Japan by our specifications.

are for long durations, more than 4~5 times longer thanOur HEFP producing system is shown schematically in Fig. 3.

the case used conventional one, although these durations

The electrode size depends

depend on the kinds of plants.

on the refrigerator size and

2. Experimental apparatus

The present experiments were conducted with two different
types of experimental apparatus: (1) well controlled refrigerator
on temperature and humidity and (2) the clean view plastic boxes
with no precise artificial control of temperature and humidityinside of the boxes left in the experimental room. In theexperiments performed so far many kinds of fresh fruits,
vegetables and flowers were tested, but in most of the cases only
the data on the change of outside shape were photographed, andno precise data such as weight change, ethylene gas discharging
rate and condition of bacteria avoidance were taken. However wehave tried to take precise data using limited kinds of fruits and theresults will be introduced.
The schematic structure of the refrigerator is shown in Fig.2.
The typical sizes used in the present experiments are 2 m (W) x 2m (D) x 2 m (H). The air is circulating within the refrigerator

several types are employed.
The outer electrodes are
made of grounded copper

Fig.3. High Electric-Field Plasma
system.

mesh, while an inner electrode is made of copper wire foldedwith 3 cm separation. The gap distance between electrodes isabout 1.0 mm. Between electrodes high voltage pulse with risetime of 0.5 μs and pulse width of 1.0 μs is applied. The pulse
height is 2.0 kV in peak and the peak current is about20  30 μA with repetition of ~ 150 Hz. These conditions,however, are variable depending on the conditions and sample
materials. Precise experimental results will be shown in theconference.
Reference1). C.M. Liu, Y. Nishida, K. Iwasaki, and K. Ting, IEEE Trans. on
Plasma Sci., 39, No.2, pp. 717-724. (2011).