lagi pasteurisasi

8/4/2019 lagi pasteurisasi

http://slidepdf.com/reader/full/lagi-pasteurisasi 1/13

Review

Designs of pulsed electric fields treatment chambers for liquid foods

pasteurization process: A review

Kang Huang, Jianping Wang *

College of Biosystems Engineering and Food Science, Zhejiang University, 268 Kaixuan Road, Hangzhou 310029, China

a r t i c l e i n f o

Article history:

Received 16 January 2009Received in revised form 4 June 2009

Accepted 8 June 2009

Available online xxxx

Keywords:

Pulsed electric field

Treatment chamber

Non-thermal process

a b s t r a c t

As a non-thermal pasteurization process, pulsed electric fields (PEF) technology has been receiving wide

attention. This rapid process can provide consumers with microbiologically safe, minimally processed,

fresh-like products. The treatment chamber, which houses electrodes and delivers a high voltage to a

food material, is one of the key components in the PEF pasteurization process. This paper mentions

the current designs of the PEF treatment chambers, reviewing various configurations of static and contin-

uous-flow treatment chambers, the effect of basic design parameters, and the performance of the opti-

mized treatment system based on the existent chambers.

Ó 2009 Elsevier Ltd. All rights reserved.

Contents

1. Introduction . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 00

2. Static treatment chambers. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 00

2.1. U-shaped static treatment chamber. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 00

2.2. Parallel plate static treatment chamber. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 00

2.3. Disk-shaped static treatment chamber . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 00

2.4. Wire–cylinder static treatment chamber. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 00

2.5. Rod–rod static treatment chamber . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 00

2.6. A sealed static treatment chamber. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 00

3. Continuous-flow treatment chambers . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 00

3.1. Electric-field strength . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 00

3.2. Treatment time . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 00

3.3. Treatment temperature. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 00

3.4. The effective area of flow . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 00

3.5. Cooling system . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 00

3.6. Coaxial treatment chambers. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 00

3.7. The flow rate and commercial PEF treatment plant . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 00

4. Conclusions. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 00

Acknowledgements. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 00References . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 00

1. Introduction

In recent years, there has been an increasing consumer demand

for fresh-like food products, especially liquid foods, such as vegeta-

ble juice, fruit juice, and milk, which are rich in antioxidant vita-

mins, for example vitamins C and E, phenolic compounds, and

carotenes (Torregrosa et al., 2006; Burns et al., 2003; John et al.,

2002; McCall and Frei, 1999; Sanchez-Moreno et al., 2003; Wil-

liamson, 1996). Therefore, keeping original flavor and color charac-

teristics as well as a high nutritive value during the food processing

is of growing importance. Traditionally, the inactivation of micro-

organisms is carried out by thermal treatment, but heat produces

alterations to flavor and taste in addition to nutrient loss (Martin

0260-8774/$ - see front matter Ó 2009 Elsevier Ltd. All rights reserved.doi:10.1016/j.jfoodeng.2009.06.013

* Corresponding author. Tel./fax: +86 571 86971713.

E-mail address: [email protected] (J. Wang).

Journal of Food Engineering xxx (2009) xxx–xxx

Contents lists available at ScienceDirect

Journal of Food Engineering

j o u r n a l h o m e p a g e : w w w . e l s e v i e r . c o m / l o c a t e / j f o o d e n g

ARTICLE IN PRESS

Please cite this article in press as: Huang, K., Wang, J. Designs of pulsed electric fields treatment chambers for liquid foods pasteurization process: A review.

Journal of Food Engineering (2009), doi:10.1016/j.jfoodeng.2009.06.013

http://dx.doi.org/10.1016/j.jfoodeng.2009.06.013

mailto:[email protected]

http://www.sciencedirect.com/science/journal/02608774

http://www.elsevier.com/locate/jfoodeng



http://www.elsevier.com/locate/jfoodeng

http://www.sciencedirect.com/science/journal/02608774

mailto:[email protected]




et al., 1997). As an alternative to the conventional methods, PEF has

been studied as a non-thermal food preservation method for food

pasteurization process (Yeom et al., 2000; Hoover, 1997).

In general, PEF treatment systems consist of a pulse generator,

treatment chambers, a fluid-handing system, and monitoring sys-

tems (Min et al., 2007), in which a PEF treatment chamber is used

to house electrodes and deliver a high voltage to the food material

and the chamber, generally, is composed of two electrodes held inposition by insulating material, which forms an enclosure contain-

ing food material. Thus, the design of the treatment chamber is one

of the pivotal factors in the development of the PEF treatment for

non-thermal pasteurization technology (Alkhafaji and Farid,

2007), because it should impart uniform electric field to foods with

a minimum increase of the temperature and the electrodes should

be designed to minimize the effect of electrolysis (Buta and Tau-

scher, 2002).

The PEF technology is desirable for liquid food to increase its

shelf life while maintaining its organoleptic characteristics. In or-

der to meet these requirements, various laboratory and pilot scale

PEF treatment chambers, developed by a number of universities,

research groups and private industries, have been designed, con-

structed, manufactured and used for non-thermal treatment on

microbial inactivation of liquid foods. During the past five decades,

a significant effort has been made to use the technologies on a

commercial scale for pasteurization of food, including some recent

industrial scale PEF treatment systems available, involving both

treatment chambers and power supply equipment (Buta and Tau-

scher, 2002).

The PEF treatment process may be either static or continuous.

While in the static processing, discrete portions of fluid foodstuff

are treated as a unit by subjecting all of the fluid to a PEF treatment

chamber, in which uniform field strength substantially is applied

to all elements of foodstuff to be treated, in the continuous pro-

cessing, the treated foodstuff is flowing into and emitted from

the PEF treatment system in a steady stream by a pump (Dunn

and Pearlman, 1987), and the design of the treatment chamber is

a gradual development from static treatment chambers to contin-uous treatment chambers.

2. Static treatment chambers

2.1. U-shaped static treatment chamber

The earliest chambers, designed in 1960s to treat food in a con-

fined, static volume was first studied by Sale and Hamilton for the

inactivation of microorganism in a static PEF chamber, which con-

tains two carbon electrodes backed with brass blocks hollowed out

for coolant flow with a U-shaped polythene spacer placed between

the electrodes to form the chamber (Fig. 1). Maximum electric field

of 30 kV/cm can be applied due to the electrical breakdown caused

by the air above the food (Alkhafaji, 2006). A maximum of 10 kV

pseudosquare wave pulses with 2–20 ls pulsewidth were tested,

in which with 10 pulses of 20 kV/cm peak field and 20 ls pulse-

width, an Escherichia coli survival rate of less than 1% was obtained

(Sale and Hamilton, 1967a). Using this treatment chamber, the

temperature rise of the suspension was small and did not cause

the lethal effect. Sale and Hamilton proposed that death of the

organisms was not because of the products of electrolysis, but be-

cause of the electric field causing an irreversible loss of the mem-

brane’s function as the semipermeable barrier between the

bacterial cell and its environment, ending in cell death (Sale and

Hamilton, 1967b).

2.2. Parallel plate static treatment chamber

Some of the first designs incorporated parallel plate geometry

using flat electrodes separated by an insulating spacer (Dunn,

2001), where uniform electric-field strength can be achieved by

parallel plate-electrodes with a gap sufficiently smaller than the

electrode surface dimension. One apparent disadvantage in this de-

sign, however, is its inherent field strength limitation due to sur-

face tracking on the fluid or insulator that leads to arcing.

A laboratory scale PEF treatment static test apparatus, designed

by Dunn and Pearlman (1987), as presented in Fig. 2, consisted of

two substantially parallel stainless steel electrodes with a gap of

5 mm and an acrylic Plexiglas electrode spacer. The chamber had

an effective electrode area of 20 cm2 with a height of 2 cm and

an inner diameter of 10 cm, with a small hole in one of the elec-

trodes, through which a liquid foodstuff to be treated was injected

to fill the chamber completely. Applied peak field strength ranged

Fig. 1. Static PEF treatment chamber designed by Sale and Hamilton (1967a,b). (a) Cut-away view showing the alignment of three parts. (b) U-shaped spacer and coolantconnection.

Fig. 2. Cut-away cross-section of the static treatment chamber designed by Dunn

and Pearlman (1987).

2 K. Huang, J. Wang / Journal of Food Engineering xxx (2009) xxx–xxx

ARTICLE IN PRESS







from 5 to 25 kV/cm. Once electric-field strength was greater than

30 kV/cm, sparks were observed.

Similar to the treatment chamber by Sale and Hamilton, the PEF

treatment chamber designed by Grahl and Markl (1996), was com-

prised of two rectangular carbon–brass electrodes separated by a

rectangular Plexiglas frame with a thickness of 0.5 or 1.2 cm. The

effective area of the electrode was 50 cm2 and the maximum volt-

age ranged from 5 to 15 kV. So the maximum electric-field strengthcould reach 30 kV/cm without cooling the electrodes.

Treatment chambers with parallel plate-electrodes provide a

uniform electrical-field distribution along the gap axes and elec-

trode surfaces, but create a field enhancement problem at the edge

of the electrodes.

2.3. Disk-shaped static treatment chamber

It is important that the PEF treatment chamber should be de-

signed to provide a high, relatively spatially uniform electric field

in the treatment zone, while minimizing the capacity or conditions

for electrical breakdown and is also important that the electrode

surface should be designed to minimize field enhancement that in-

creases the local electric field and results in electrical breakdown

(Bushnell et al., 1993). To minimize the potential for electrical

breakdown at the insulator, proposed were principles which are

instrumental to successful processing at high electric-field

strengths (Bushnell et al., 1993). Such principles are (1) removing

the insulator from the region of high electric field, (2) removing

the ‘‘triple point” (i.e., the interface between the electrode, insula-

tor, and liquid or pumpable food) from the high field region, (3)

increasing the length of the insulator, (4) placing the insulator at

an angle to the electric field, and/or (5) reducing electric field

enhancement by appropriate design of the shape of the electrodes.

In accordance with the principle (5) mentioned above, the de-

sign of disk-shaped, round-edged electrodes can reduce electric

field enhancement and the possibility of electric breakdown of

the fluid foods (Dunn and Pearlman, 1987).

Washington State University (WSU) designed a disk-shaped sta-tic chamber (Fig. 3), where two round-edged disk-shaped stainless

steel electrodes polished to mirror surfaces were held in position

by insulting material that also formed an enclosure containing

the food (Qin et al., 1994). Because the disk-shaped, round-edged

electrodes minimized electric field enhancement and reduced the

possibility of dielectric breakdown of the fluid foods and polysulf-

one or Plexiglas was selected as insulating materials. The appear-

ance of space charge in the food would modify the electric field

from the ideal no-space-charge situation. Accordingly, the gap be-

tween the two electrodes and the volume of the chamber were

0.51 cm and 13.8 ml or 0.95 cm and 25.7 ml, and the maximum

electric-field strength reached 75 kV/cm. There was also a cooling

system in this chamber, which was provided by circulating water

at pre-selected temperatures through jackets built into theelectrodes.

To investigate inactivation of E. coli O157:H7 suspended in dia-

lyzed liquid egg products, Amiali et al. (2004) developed a static

treatment chamber, in which the 0.23 ml treatment chamber con-

sisted of two parallel stainless electrodes and polypropylene spacer

with 0.15 cm gap and 1.53 cm2 surface areas (Fig. 4), with a cooling

system used to maintain constant temperature during the PEF

treatment (Amiali et al., 2004). A three log reduction in counts of

E. coli O157:H7 in liquid egg yolk was obtained at 0 °C using PEF

treatment of 15 kV/cm, 500 pulses and 200 ls pulsewidth.

2.4. Wire–cylinder static treatment chamber

As showed in Fig. 5a, a wire–cylinder electrode system was used

in the experiment, where the inner diameter of the cylinder elec-

trode was 20 mm, and the wire diameter was 1 mm, and the length

of the treatment chamber was 110 mm, which could contain

38 cm3 of liquid (Matsumoto et al., 1991). The wire electrode

was held by Plexiglas cap at the top of the center of the cylinder,

with this treatment chamber mounted on the stirrer at the bottom

of the cylinder. It became obvious from a solid liner in Fig. 6 that

destruction performance markedly deteriorated with decrease of

survivability. To improve this performance deterioration, a stirrer

was used to promote the agitation of the liquid, so that once the

liquid in the cylinder was effectively agitated, the survivability lin-

early decreased 10À

4–10À

5 with increase of energy input, but theagitation of the liquid would cause another problem: the electric

field was essentially distributed inside the wire–cylinder electrode.

Because the electric field near the cylinder wall was much lower

than that near the wire electrode, destruction performance in this

area would be low.

2.5. Rod–rod static treatment chamber

A rod–rod treatment chamber, in which a pair of rod electrodes

were screwed to the Teflon chamber and held at the center of the

chamber (Fig. 5b), was made to study the cell destruction by an in-

tense shock wave generated by an underwater arc discharge. With

a diameter of 4 mm for each rod electrodes, and the rod end in the

shape of a semi-sphere, the distance between the two rod elec-trodes was 3 mm. The nylon film was away from the discharge

point by 15 mm, and the inner diameter and the length of the small

vessel for sample liquid were 15 mm respectively (Matsumoto

et al., 1991).

2.6. A sealed static treatment chamber

Application of PEF processing is restricted to food products with

no air bubbles (Ramaswamy et al., 2005), because in the treatment

chambers, the uniformity of the electric field can be easily influ-

enced due to the presence of gas-filled cavities such as gas bubbles

(Gongora-Nieto et al., 2003), and the presence of a gas bubble in-

side the chamber will cause local dielectric breakdown, thus

threatening the uniformity of the PEF treatment across the cham-ber gap, and even successive applications of PEF will result in aFig. 3. Schematic drawing of WSU static treatment chamber (Qin et al., 1994).

Fig. 4. Static treatment chamber designed by Amiali et al. (2004).

K. Huang, J. Wang / Journal of Food Engineering xxx (2009) xxx–xxx 3

ARTICLE IN PRESS







spark (Alkhafaji and Farid, 2007). Based on theories describing

dielectric breakdown in liquid dielectrics (Gallagher and Pearmain,

1983), entrapped gas bubbles in liquid food flowing through thegap of a PEF treatment chamber were considered to be the reason

for local dielectric breakdown and discharge of the system, a lim-

iting factor in PEF technology (Gongora-Nieto et al., 2003). Consid-

ering the potential trigger of dielectric breakdown, the filling port

should facilitate the complete expelling of air during the filling

process.

When the food product experiences a spark in a sealed static

treatment chamber, high pressure develops rapidly and the cham-

ber may break apart. Thus, a degassing unit is desirable to ensure

safety of the operation, eliminating the possibility of dielectric

breakdown within the treated liquid to the minimum during pro-

cessing (Zhang et al., 1995; Alkhafaji and Farid, 2007).

This static treatment chamber held a volume of 60Â 60Â

3 mm3 (Fig. 7). Two parallel electrodes, whose thickness was

1 mm here, were made of stainless steel. High temperature resist-

ing material PTFE (polytetrafluoroethylene) was used for the dis-

charging chamber. In order to prevent the bacteria influencing

the result of the experiment, the static treatment chamber was

completely sealed, and sample liquids were taken using a medicalsyringe. Owing to relatively larger volume of the chamber, wave-

form of high voltage pulse, to a large extent, was affected by the

equivalent circuit parameters of the chamber. The actual pulse

voltage was lower than voltage produced by capacitor discharge.

Accordingly, the inactivation of microorganism was less effective

(Fang et al., 2006; Zhang, 2005). Based on this design, Bazhal

et al. (2006) used a batch treatment chamber with a cooling system

to study the efficiency of the combined thermal and PEF inactiva-

tion of E. coli O157:H7. In line with the above viewpoint, relatively

lower electric field intensities, ranging from 9 to 15 kV/cm, were

obtained in this chamber.

In addition, materials of the PEF treatment chamber should be

washable and autoclavable. Usually, satisfactory results will be ob-

tained from some food stuffs at some voltage levels, while theapparatus may be constructed using stainless steel electrodes

and polysulfone insulation (Hofmann, 1984), while in other envi-

ronment more inert electrode materials, such as gold, platinum,

carbon and metal oxides, may provide improved performance

(Bushnell et al., 1993).

Static chambers are mainly suitable for laboratory use, to find

out the relevant factors parameters, while for large scale opera-

tions, continuous chambers are more efficient. Thus in the initial

stage of the researches, the establishment of static treatment

chamber is indispensable.

3. Continuous-flow treatment chambers

Actually, most continuous-flow treatment chambers borrowideas from the static chamber designs, or more exact, a number

Fig. 5. Static treatment system designed by Matsumoto et al. (1991). (a) Wire–cylinder electrode and (b) rod–rod electrode system.

Fig. 6. Effect of agitation on the survivability of S. cerevisiae (Matsumoto et al.,1991).

Fig. 7. Sketch map of static treatment chamber designed by Zhang (2005).


ARTICLE IN PRESS







of continuous-flow treatment chambers were modified from some

similar static treatment chambers, in which PEF treatments per-

formed more effectively using continuous treatment chambers,

due to the great treatment uniformity in the continuous systems

(Martin et al., 1997).

The proper design of the treatment chamber is essential for the

efficiency of the PEF technology (Narsetti et al., 2006), as the effi-

ciency of the microbial inactivation by PEF is determined by three

factors that are classified with treatment parameters, product

parameters, and microbial characteristics, as shown in Table 1

(Min et al., 2007). Of these factors, only treatment parameters

can be modulated in treatment chambers. The main treatment

parameters that influence the inactivation rate of microorganisms

by PEF include electric-field strength, PEF treatment time, pulse-

width, pulse shape, treatment temperature, and inlet temperature

(Knorr et al., 1994; Hulsheger and Niemann, 1980). Generally, asthe intensity of each of these parameters increases in a certain

range, the microbial inactivation by PEF also increases. The at-

tempts, which have been made by studies on the optimization of

the treatment parameters to obtain better performance of the

PEF processing, are classified as below.

3.1. Electric-field strength

Electric-field strength and treatment time are the most impor-

tant treatment parameters affecting the performance of microbial

inactivation by PEF (Castro et al., 1993). Of all the factors influenc-

ing microbial inactivation by PEF, the effect of electric-field

strength is the most obvious. Once the applied electric field ex-

ceeds a critical value for sufficient time, transmembrane potentialis induced which results in cell death (Alkhafaji, 2006). A log–linear

relationship between electric-field strength and microbial inacti-

vation was reported (Hulsheger and Niemann, 1980; Reina et al.,

1998; Bruhn et al., 1997; Qin et al., 1998), obviously indicating that

the efficiency of pulse treatment strongly depends on the field

strength applied, as presented in Fig. 8, left (Heinz et al., 2003).

The higher the field strength at constant energy levels, the higher

is the lethality of the treatment, with the studies on the effect of

PEF treating fluid foodstuff showing that the killing power in-

creases more with electric-field strength than with pulse duration

(Schoenbach et al., 2000).

An interesting design for a treatment chamber which provides

higher electric fields in a small volume without increasing the volt-

age at the electrodes was proposed by Matsumoto et al. (1991) toobtain higher electric-field strength in a ‘‘Converged Electric Field

type” treatment chamber, in which the insulating plate (Teflon)

with small holes was placed between the parallel disc electrodes

(Fig. 9). The inner diameter of the vessel was 20 mm, and the dis-

tance between the disc electrodes was also 20 mm, with the stan-

dard thickness of Teflon plate of 10 mm, but the diameter and

number of the hole being varied. Though the liquid was continu-

ously introduced into the vessel through the hole of the disc elec-

trodes, only the fluid inside the holes of the insulating plate was

subjected to the PEF treatment. Since the cross-section area of

the holes was very small, the electric field lines were mainly con-

centrated at the hole part, where the cell suspension flowed. At the

moment, the fluid at both sides of the small holes actually acted as

electrodes, and the length of the small holes corresponded to the

distance between the two electrodes. The current density at the

electrode–liquid interface was held low to minimize electrolysisand reduce possibility of bubble formation. Compared with the

wire–cylinder static treatment chamber, in the ‘‘Converge Electric

Field type” treatment chamber, performance was improved and

survivability decreased, as showed in Fig. 10, but with a disadvan-

tage that in this design the stagnant zones in the 90° corners of the

cell, where microbes could build up and liquid food might overheat

undesirably, would cause sparking (Alkhafaji, 2006).

Compared with the larger electrode surface, the treatment area

and gap between the electrodes should be small in order to have a

uniform and strong electric field (Qin et al., 1994), accordingly, a

continuous co-field PEF treatment chamber was designed and con-

structed by Sensoy et al. (1997), as shown in Fig. 11, the actual

treatment volume was the small orifice volume. The volume of

Table 1

The factors determining the efficiency of the microbial inhibition by PEF.

Factors Parameters References

Treatment

parameters

Electric-field strength Ortega-Rivas et al.

(1998)

PEF treatment time Odriozola-Serrano

et al. (2006)

Treatment temperature Lebovka et al. (2004)

Pulsewidth Wu et al. (2005)Pulse shape Fox et al. (2007)

Product

parameters

Electric conductivity Vega-Mercado et al.

(1996)

Density Beebe et al. (2002)

Viscosity Ruhlman et al. (2001)

pH Garcia et al. (2005)

Water activity Min et al. (2007)

Microbial

characteristics

Microbial cell size and sharp Wouters et al. (2001)

Gram-positive bacteria or gram-

negative bacteria

Lado and Yousef

(2002)

Growth stage of microorganisms Pothakamury et al.

(1996)

Fig. 8. Inactivation of E. coli HB5a in response to high intensity pulsed electric field

treatment in a continuous-flow system (Heinz and Knorr, 2000).

Fig. 9. Structure and equivalent circuit of converged electric field type treatmentchamber (Matsumoto et al., 1991).


ARTICLE IN PRESS







the orifice and the conical regions were designed so that the volt-

age across the orifice would be high enough for inactivation, with

electric-field strengths of 25–40 kV/cm being tested. The special

conical shaped electrodes and insulators were designed to elimi-

nate gas deposits within the treatment volume, resulting in

increasing the electric-field strength which increases the inactiva-

tion rate logarithmically, consistent with the conclusion by Hul-

sheger and Niemann (1980), Reina et al. (1998), Bruhn et al.

(1997) and Qin et al. (1998). The problem of stagnant zone in the

previous design was prevented, but again, the liquid in the center

of the cell would receive less electric pulses, while the treatment

outside the disc electrode was important.

Similar to the previous design, presented by Alkhafaji and Farid

(2007), another design to concentrate the electric field in a smallregion consisting of a treatment chamber includes two stainless

steel mesh electrodes isolated from each other by an insulator ele-

ment designed to from an orifice where the voltage across the ori-

fice is close to the supplied voltage (Fig. 12), where the liquid food

was introduced from the openings of the two mesh electrodes and

through the orifice between them where the electric field lines

were concentrated. The treatment volume in the chamber was

0.06 cm3, and the unit was designed for flow rate of 2.5 cm3/s, to

provide a residence time of 0.026 s in the treatment zone, so that

the problem of the stagnant zone where microbes could build up

and the liquid food might overheat was minimized in the present

design.

3.2. Treatment time

As the PEF treatment time increases, the inactivation rate of mi-

crobes was rapid incipiently, and then gently, gradually flattening,

finally, no significant change even treated with more time ( Jayaram

et al., 1992), with the microbial killing highest during the first 10–

20 pulses and gradually decreasing (Alkhafaji and Farid, 2007). Thetreatment time is calculated by multiplying the number of pulses

applied by the pulsewidth, because the pulsewidth and/or the

number of pulses increase, the PEF treatment time will also in-

crease, which results in an increased microbial inactivation. Never-

theless, it is necessary to avoid increasing pulsewidth to a fault,

because it will cause food temperature to rise to an undesirable le-

vel, so, the pulsewidth must be controlled in the range that does

not cause overheat (Zhang et al., 1995).

Dunn and Pearlman (1987) described a PEF unit in which a con-

tinuous-flow effectively ‘switches’ on and off the electric field

(Fig. 13), where fluid foodstuff was subjected to a sequential plu-

rality of high electric field pulses. The chamber included a plurality

of cylindrical shape electrode reservoir zones, which were electri-

cally isolated from each other by intervening dielectric separatingelements so that only the current will pass through the fluid food-

stuff itself. Typical operating conditions for the system were elec-

tric-field strengths from 5 to 25 kV/cm with square or

exponentially decaying pulse shapes, typical duration between 1

and 100 ms, and repetition rates between 0.1 and 100 Hz. As indi-

cated, it is important that a substantially uniform electric field be

provided throughout the liquid foodstuff treatment zone. Other-

wise, current filaments or the formation of ‘‘streamer” arcs may de-

velop within the treatment zone, but the present design could not

provide uniform treatment so that the product had the trend to

produce current filaments or arcs.

Washington State University (WSU) PEF research group de-

signed, constructed and tested a bench scale continuous-flow

chamber, which was modified from the above-mentioned WSUstatic treatment chamber. To increase the residence time of the li-

Fig. 11. Side view of the treatment chamber designed by Sensoy et al. (1997).

Fig. 12. Cross sectional view of the PEF treatment chamber designed by Alkhafaji

and Farid (2007).

Fig. 10. Electrode type and survivability of S. cerevisiae (Matsumoto et al., 1991).


ARTICLE IN PRESS







quid food inside the treatment chamber, baffled flow channels

were added inside the chamber, providing a tortuous path of liquidfood in the treatment zone (Fig. 14). Cooling of the chamber was

provided by circulating water at a selected temperature through

jackets built in the two stainless steel electrodes. The designed

operating conditions were chamber volume 20 or 8 cm3; electrode

gap 0.95 or 0.51 cm; PEF strength 35 or 70 kV/cm; pulsewidth 2–

15 ls; pulse repetition rate of 1 Hz; and food flow rate of 1200

or 600 cm3/min.

3.3. Treatment temperature

The treatment temperature also plays an important role in

microbial inactivation (Floury et al., 2006). Application of PEF at

mild temperatures has been suggested as a way to enhance the

effectiveness of PEF as a preservation method (Sepulveda et al.,2005), but the effect of the temperature on inactivation is compli-

cated. On the one hand, higher temperature will induce damage in

organoleptic qualities of food, while on the other hand, numerous

researches have been made, finding that increasing the inlet tem-

perature (from 22 to 50 °C) would lead high killing rate (Sensoy

et al., 1997; Reina et al., 1998; Calderon-Miranda et al., 1999). Pre-

ferred temperature for the treatment chamber and electrodes are

in the range of approximately 0–65 °C, preferably 10–45 °C, even

more preferably 15–25 °C (Qin et al., 2000). Moreover, it was sug-

gested that PEF treatment be combined with thermal treatment

(Hulsheger et al., 1981; Mertens and Knorr, 1992; Lebovka et al.,

2004), because if the food temperature was raised before a PEF

treatment, the food product would get less thermal load in this

way compared with the product undergoing a PEF treatment with-out preheating (Heinz et al., 2003). Using synergistic effects of ele-

vated treatment temperature on microbial inactivation, the energy

input could also be reduced from above 100 to less than 40 kJ/kg,

leading to a drastic reduction in operation costs (Heinz et al.,

2003). Zhang et al. (1995) found that increasing the inlet tempera-

ture from 7 to 20 °C significantly increased the PEF inactivation of

E. coli in simulated milk ultra filtrate, but the additional increase in

temperature from 20 to 33 °C did not result in an increase in PEF

inactivation. Thus, the inlet temperature plays a second role in

microbial inactivation (Floury et al., 2006).

Mcdonald et al. (2000) developed two continuous-flow Cool-PureTM PEF systems, namely the pilot PEF system (CPSI) and the

Fig. 13. A continuous current, high electric field treatment chamber (Dunn and Pearlman, 1987). (a) Chamber and (b) electric field versus time or position as fluid switching.

Fig. 14. WSU continuous treatment chamber with baffles. (a) Cross-section view. (b) Top view (Zhang et al., 1995).

Fig. 15. Line drawing of the CPSI chamber and the LP treatment chamber

(Mcdonald et al., 2000).


ARTICLE IN PRESS







PurePulse Laboratory Prototype PEF system (LP), as presented in

Fig. 15. In both the CPSI and LP systems, product was heated and

cooled using tube-in-tube heat exchangers, in which directly be-

fore the product was pumped into the PEF treatment chamber, it

was heated to 30 °C, and the cooling heat exchangers after the

PEF treatment chamber decreased product temperature to be-

tween 4 and 7 °C, with the product reaching the cooling heat

exchangers about 13 s after treatment.

Overall, the PEF treatment combining heat processing has sig-

nificant and sometimes damaging effects upon the taste, color,

and other properties of the resultant food products (Qin et al.,

2000). Since thermal damage to freshly squeeze fruit juice is min-

imal at temperature below 50 °C (Innings, 1998), process condi-

tions should be maintained at or below this temperature.

In the PEF treatment system designed by Yin et al. (1997), an

extension of the number of treatment chambers in series was men-

tioned (Fig. 16). The heat exchangers, as shown in Fig. 17, are in

physical connection with PEF treatment devices, so that the three

heat exchangers were located before each treatment chamber

respectively, and different combinations involving more or lessheat exchangers and PEF treatment devices were possible, where

the heat exchangers primarily served as temperature regulators

for the PEF treatment system. Intermediate cooling was applied

to remove the heat deposited in the product after each treatment,

so that the temperature increment across each individual treat-

ment chamber in this system was of less importance. However,

the non-uniformity of the electrical-field distribution remained

(Mastwijk and Bartels, 2001).

3.4. The effective area of flow

Morshuis et al. (2002) outlined an apparatus for preserving food

products in a pulsed electric field comprising a treatment chamber

with an inlet for food products to be treated and an outlet for trea-ted food products as well as a larger effective area of flow (Fig. 18).

Consisting of a circular tube, the treatment chamber was fabricated

from an electrically nonconductive material and was provided with

a group of electrodes which were distributed, spaced regularly

with respect to one another, over a first section of the inside of

the chamber, and with another group of electrodes which were dis-

tributed, spaced as the same as the first group, over a second of the

inside of the chamber. All the electrodes, insulated from each

other, extended parallel to the longitudinal center line of the treat-

ment chamber. As shown in Fig. 18, the electrodes had a crescent-

shaped (half-moon) cross-section, of which one side had a radius of

curvature which was equal to the radius of the internal perimeter

of the treatment chamber, said side forming part of the internal

perimeter of the chamber. The treatment chamber therefore hada smooth inner surface, thus without perturbing on the flow of a

product to be treated. In this treatment chamber design, the elec-

trodes were installed in such a way that the field lines of the elec-

tric field ran parallel to one another and potential controller was of

such a design that the electric field in the effective area of flow was

uniform, without the risk existing in a known apparatus, that

undesirable contaminants, for example microbes would accumu-

late in the corners of the container (Geren, 1984).

3.5. Cooling system

The change in temperature during the PEF processing should be

monitored and controlled to achieve a non-thermal operation, be-cause the unavoidable difference between the inlet and outlet tem-

Fig. 16. A schematic illustration of the PEF system for extending the shelf life of liquid products ( Yin et al., 1997).

Fig. 17. Heat exchangers of pilot plant scale PEF system manufactured by OSU

(<http://fst.osu.edu/pef> ).

Fig. 18. PEF treatment chamber (Morshuis et al., 2002).


ARTICLE IN PRESS



http://fst.osu.edu/pef






perature is due to heat dissipation in the product as a result of oh-

mic heating (Alkhafaji and Farid, 2007).

High voltage pulses produced by capacitor discharge contain a

finite amount of energy (Q pulse) that reaches the treatment cham-

ber, as defined (Sepulveda et al., 2005):

Q pulse ¼RCh

RT

CV 2

2ð1Þ

where C is the capacitance of the discharging capacitor, V is the

charging voltage, RCh is the electrical resistance of the treatment

chamber and RT is the total electrical resistance of the system

through which the capacitor is being discharged. Repetitive applica-

tion of high voltage pulses causes heating of the treated product

(DT ) as energy is released into the treated product as defined ( Sep-

ulveda et al., 2005):

DT ¼ fQ pulseF qC p

ð2Þ

where f is the pulsing frequency, F is the flow rate of the liquid prod-

uct pumped through the treatment chamber, q is the density of the

treated product, and C p is its specific heat.

To maintain the fluid within the designed temperature rangeduring the PEF treatment processing, a cooling system is desirable,

which, by a heat exchange, was located either in the treatment

chamber itself, or between treatment chambers in the case of sys-

tems with more than one treatment chamber usually employed

(Evrendilek and Zhang, 2005;. Sepulveda et al., 2005; Cserhalmi

et al., 2006; Torregrosa et al., 2006).

For example, a coaxial PEF treatment chamber was developed to

treat fluid products (Pizzichemi and Occhialini, 2007), concerning

which a drawing is shown in Fig. 19, and with a movable internal

electrode, the PEF treatment chamber could allow us to adapt to

many values of resistivities. Moreover, particular attention was gi-

ven to the design of an appropriate cooling system, in order to con-

trol the temperature inside the chamber, and to the sealing of the

treatment zone.

3.6. Coaxial treatment chambers

The aim of the PEF treatment chamber design is to achieve a rel-

atively uniform high voltage electric field in the treatment region.

Because of the shape of the electrodes, an uneven distribution of

electric field could occur, which may cause local electric field

enhancement (Ge, 2005).

For medium-size volumes, coaxial treatment chambers can beeasily manufactured and give well-defined electric field distribu-

tion (Hofmann, 1989). The field strength between coaxial elec-

trodes is:

E ¼V

r ln R2R1

ð3Þ

where r is the radius at which electric field is measured. R1 and R2

are the radius of the inner and outer electrode surface, respectively.

Although the electric field in coaxial chambers is not completely

uniform, this kind of treatment chamber received extensive atten-

tion due to its simple configuration and homogeneous fluid flow.

Generally, the coaxial treatment chamber consisted of two

cylindrical electrodes made of stainless steel, of which the inner

electrode was connected to a high voltages supply and the outerelectrode to the ground, and the spacer between the inner and

the outer electrodes allowed liquid food to flow through (Esplugas

et al., 2001).

In coaxial treatment chambers, the uniformity of the electric

field can be easily altered due to protuberances on the chamber

electrodes or due to the presence of gas-filled cavities such as

gas bubbles. Based on theories proposed by Gallagher and Pear-

main (1983), the gas bubbles in liquid food would cause local dis-

Fig. 19. PEF coaxial chamber designed by Pizzichemi and Occhialini (2007).Fig. 20. Electric field region between high voltage electrode and groundedelectrode in the coaxial treatment chamber (Qin et al., 1997).


ARTICLE IN PRESS







charge and dielectric breakdown, and dielectric breakdown can

further limit the effectiveness of process and lead to increased pro-

cessing steps, processing time, processing energy needed in an ef-

fort to successfully inactivate microbes or enzymes contained in

the food being treated (Qin et al., 2000).

A continuous treatment chamber based on a modified coaxial

cylinder arrangement was designed and manufactured (Qin et al.,

1997), as illustrated in Fig. 20a, in which liquid food was continu-ously introduced into a treatment zone between two coaxial elec-

trodes with an optimized configuration. Electric field optimization

technology was used to modify the configuration of the electrodes

(Misaki et al., 1982). The final electrode configuration in the treat-

ment region is illustrated in Fig. 20b, where the shaded area repre-

sents a dielectric material (Plexiglas) used to form the liquid flow

path (Qin et al., 1998). The protruded surface located at the outer

electrode enhanced the electric field within the treatment zone

and reduced the field intensity outside the treatment zone. Both

the inner high voltage electrode and the outer grounded electrode

contained circulating cooling fluid for controlling the temperature

of electrodes (Qin et al., 1995, 1998). In the treatment region, the

electrical potential drop was nearly uniform and a strong electric

field was generated. What’s more, the coaxial treatment chamber

may operate normally without dielectric breakdown even at an

electric field exceeding 70 kV/cm. Another advantage of this design

was that the optimized configuration would reduce the risk of elec-

trical discharge through the food product being treated signifi-

cantly. Remarkably resulting in reducing field strength between

the electrodes, however, it created a risk that microbes in the food

product might not be inactivated adequately as they pass through

the treatment zone (Qin et al., 2000).

The intent of food pasteurization with PEF is to induce the

dielectric breakdown of the cell membrane, rather than the dielec-

tric breakdown of the fluid food, or termed spark-over, which

should be prevented in the PEF pasteurization (Zhang et al., 1995).

To treat food products of high electric conductivity specially, a

further preferred treatment chamber was built, different from the

previous one with respect to the surface of the inner and outer elec-trodes in the treatment zone, where instead of the parallel annular

faces used in previous chamber, the treatment faces of electrodes

were specially contoured to provide a treatment zone in which

the electrical-field strength varied between relatively higher values

and relatively lower values. The relatively higher electric field was

associated with the points of the primary treatment zone where

the complementary electrode faces were closely spaced. The rela-

tively lower electric field was associated with the points of the pri-

mary treatment zone where the complementary electrode faces

were relatively further spaced. As shown in Fig. 21, the treatment

zone complementary electrode faces were provided with a longitu-

dinally scalloped face shape, so that the convoluted face shapes of

each side were in complementary registration with the further

extension of each face in axial alignment. The electrode configura-tion increased the effective electrical resistance across the treat-

ment chamber without reducing the processed fluid path length

through the treatment zone, consequently reducing the power load

on thecircuitry used to drive the electrodes. Additionally, theundu-

lating electrodes surfaces induced additional agitation in the fluid

being processed, believed to have beneficial effects on microbial

inactivation (Qin et al., 2000).

Bushnell et al. (1993) designed a coaxial treatment chamber to

provide a high, relatively spatiallyuniform electric field in thetreat-

ment zone, minimizing its capacity for electrical breakdown. To

accomplish this objective, the insulator separating electrodes of

appropriate electrical polarity was removed from the high field re-

gion to avoid breakdown produced by electrical tracking or flash-

over along the insulator surface. The electrode surfaces were

designed to minimize field enhancement, aiming to avoid the elec-

tric field locally increasing and electrical breakdown. The design

used an appropriate geometry to assure that all the pumpable food

could pass through the electric field treatment zone before exiting

the treatment chamber. It is also important that in this design, ex-

cept for the inclusion of an inlet or outlet port, one end of the coax-

ial arrangement was closed, so that field fringing is reduced, which

could be further reduced with the proper choice of materials. How-

ever, the major disadvantage of the chamber was the limited width

of the annulus through which the liquid could flow and the rela-

tively large electrode surfaces (Mastwijk and Bartels, 2001).

To solve the above problem, Mastwijk and Bartels (2001) devel-

oped the treatment chamber (Fig. 22) with cylindrical cross-sec-

tions and consisting of four modules using three annular

electrodes. Another difficulty of non-uniform distribution of theelectrical-field in the treatment zone mentioned in the treatment

chamber designed by Yin et al. (1997) was also overcome. In this

design, although the electric field distribution of a single module

was not uniform, an array of properly coupled modules considered

a uniform field was obtained over the volume of each module. The

disadvantage of this design was a slightly non-uniformity of the

electric field distribution of the first and the last cell owing to

the fact that translation symmetry in the electrode array was

absent.

3.7. The flow rate and commercial PEF treatment plant

For commercial PEF treatment plant, as one of the major factors

affecting PEF system design, flow rate of fluid foodstuff determines

Fig. 21. Across sectional view of modified coaxial treatment chambers (Qin et al.,2000). Fig. 22. Modular design of PEF treatment chamber (Mastwijk and Bartels, 2001).


ARTICLE IN PRESS







several major PEF system characteristics, such as the pipe diame-

ter, the average power required for a given fluid and protocol,

and it should be increased while the field strength is maintained.

Only in that way will the PEF treatment protocols transit from lab-

oratory and pilot scale to commercial scale operations. For exam-

ple, doubling the pipe diameter allows four times the flow at a

given pressure, but requires twice the peak voltage to maintain

the same field strength.

A laboratory system typically processes liters per hour (or less),

and a pilot plant typically operates at ten to hundreds of liters per

hour, while commercial systems, however, must be capable of pro-

cessing thousands to tens of thousands of liters per hour (Kempkes

et al., 2008). As shown in Table 2, Ohio State University (OSU) has

designed three series of PEF units that differ primarily in theirfluid-handling capacity.

Larger pipe diameters support higher flow rates, which, how-

ever, require proportionally higher pulse voltages to maintain the

same field strength. Diversified Technologies Inc. (DTI) is one of

the manufacturers that sell PEF systems. It has developed solid-

state high voltage pulsed power systems, which providing the reli-

ability and the process consistency required for commercial PEF

systems, which have treatment chamber of a co-field flow chamber

design, developed and patented by Ohio State University (OSU). As

shown in Fig. 23, this design provided an optimal balance between

the flow and field requirements, capable of maintaining consistent

field strengths, the gap over which the field is applied must be pro-

portional to the pipe diameter. This design is best utilized at 5 cm

pipe diameters and below, which translates to 200 kV pulses (at40 kV/cm) (Kempkes et al., 2008).

For sterilizing and pasteurizing foods, packaging, and other pur-

poses, advanced systems are developed and commercialized by

Maxwell’s PurePulse Technologies Inc. subsidiary, whose Cool-

PureTM PEF system is used for reduced-temperature pasteurization

of liquid food such as milk, orange juice, wine, and beer, as well

as cheese, treatment costs usually at less than $0.04 per liter. Both

CPSI and LP were developed by PurePulse, whose treatment veloc-

ity was 10 and 200 L/h, respectively. To obtain a high-capacity sys-

tem, PurePulse is working with US military organizations and other

industry groups to further research and develop advanced preser-

vation applications for this technology.

In the United States, the Natick Soldier Center, part of the US

Army Soldier Systems Center (Natick), in cooperation with indus-

try and academia, is capable of producing high-quality meals with

long shelf life. They mainly work at the study of treatment process

and treatment efficiency. Electric Power Research Institute Inc.

(EPRI) and Institute of Food Technologists (IFT) also set up research

groups to promote the PEF researches and provide the conveniencefor obtaining information.

To meet the strict microbiological requirement of Pure Food and

Drug Administration (FDA), Genesis Juice Corporation successfully

pioneered PEF patented technology into the commercially treat-

ment in 2004. The PEF treatment preserved the color, the flavor

and the concentration of nutrients. Genesis used an OSU-5 running

at about 200 L/h (Clark, 2006). PEF offered a five-log reduction of

most pathogens, and the shelf life of the products was said to be

4 weeks.

However, the electrodes of existing commercial PEF systems

need replacement about every 100 h of operation (Clark, 2006).

DTI, OSU, and others are investigating electrodes with longer life-

times. Besides, vegetable juices such as carrot with particles have

difficulty in passing through the small clearances of the treatmentchambers.

4. Conclusions

Presented in this paper, various designs of the PEF treatment

chambers are described first commenting that static chambers are

suitable for mainly laboratory use, but for commercial scale opera-

tions, continuous chambers are more efficient. For the sake of effi-

cient treatment, a large number of the basic design parameters

should be considered, such as electric-field strength, treatment

time, treatment temperature, electric field distribution etc. Based

on the previous designed treatment chambers, optimizations of

the treatment parameters have been made to achieve better perfor-

mance of the PEF processing. However, PEF treatment is not the an-swer for every food, as currently most of the treatment chambers

are only used for fluid food products. And the lethal effect of PEF

treatment is not effective on all microbes and enzyme, currently

only effective on the familiar microorganism such as E. coli and S.

cerevisiae. Besides, current PEF equipment costs arehigh, in part be-

cause of the relatively small market for the electrical equipment,

making the PEF technology only a limited success. There remain

significant engineering challenges, which is why numerous re-

search groups are still exerting themselves in this area.

Acknowledgements

The authors gratefully acknowledge the financial support pro-

vided by National High Technology Research and DevelopmentProgram (2007AA100405).

Fig. 23. Commercial co-field flow treatment chamber manufactured by DTI and

OSU, with four treatment cells. Pipe diameter is approximately 1.5 cm ( Kempkeset al., 2008).

Table 2

The different fluid-handling capacity of three PEF units designed by OSU ( <http://fst.osu.edu/pef>).

PEF system Bench top PEF system (OSU-4) Pilot plant scale PEF system (OSU-5) Commercial scale PEF system (OSU-6)

Pipe diameter (mm) 3 10 10–12

Flow rate (L/h) 3.6–36 80–200 400–2000


ARTICLE IN PRESS









References

Alkhafaji, S.R., Farid, M., 2007. An investigation on pulsed electric fields technologyusing new treatment chamber design. Innovative Food Science and EmergingTechnologies 8 (2), 205–212.

Alkhafaji, S.R., 2006. An investigation on the non-thermal pasteurization usingpulsed electric fields. The University of Auckland, New Zealand.

Amiali, M., Ngadi, M.O., Raghavan, V.G.S., Smith, J.P., 2004. Inactivation of Escherichia coli O157:H7 in liquid dialyzed egg using pulsed electric fields.

Food and Bioproducts Processing 82 (C2), 151–156.Bazhal, M.I., Ngadi, M.O., Raghavan, G.S.V., Smith, J.P., 2006. Inactivation of Escherichia coli O157:H7 in liquid whole egg using combined pulsed electricfield and thermal treatments. LWT 39, 419–425.

Beebe, S.J., Fox, P.M., Rec, L.J., Somers, K., Stark, R.H., Schoenbach, K.H., 2002.Nanosecond pulsed electric field (nsPEF) effects on cells and tissues: apoptosisinduction and tumor growth inhibition. IEEE Transactions on Plasma Science 30(1), 286–292.

Bruhn, R.E., Pedrow, P.D., Olsen, R.G., Barbosa-Canovas, G.V., Swanson, B.G., 1997.Electrical environment surrounding microbes exposed to pulsed electric fields.IEEE Transaction on Dielectrics and Electrical Insulation 4 (6), 806–812.

Burns, J., Frase, P.D., Bramley, P.M., 2003. Identification and quantification of carotenoids, tocopherols and chlorophylls in commonly consumed fruits andvegetables. Phytochemistry 62 (6), 939–947.

Bushnell, A.H., Dunn, J.E., Clark, R.W., Pearlman, J.S., 1993. High Pulsed VoltageSystems for Extending the Shelf Life of Pumpable Food Products. US Patent5,235,905.

Buta, P., Tauscher, B., 2002. Emerging technologies: chemical aspects. Food ResearchInternational 35 (2–3), 279–284.

Calderon-Miranda, M.L., Barbosa-Canovas, G.V., Swanson, B.G., 1999. Inactivation of Listeria innocua in liquid whole egg by pulsed electric fields and nisin.International Journal of Food Microbiology 51 (1), 19–31.

Castro, A.J., Barbosa-Canovas, G.V., Swanson, B.G., 1993. Microbial inactivation of foods by pulsed electric fields. Journal of Food Processing and Preservation 17(1), 47–73.

Clark, J.P., 2006. Pulsed electric field processing. Food Technology 1, 66–67.Cserhalmi, Z.S., Sass-Kiss, A., Toth-Markus, M., Lechner, N., 2006. Study of pulsed

electric field treated citrus juices. Innovative Food Science and EmergingTechnologies 7 (1), 49–54.

Dunn, J.E., Pearlman, J.S., 1987. Methods and Apparatus for Extending the Shelf Lifeof Fluid Food Products. US Patent 4,695,472.

Dunn, J., 2001. Pulsed electric field processing: an overview. In: Barbosa-Canovas,G.V., Zhang, Q.H. (Eds.), Pulsed Electric Fields in Food Processing. TechnomicPublishing Company Press.

Esplugas, S., Pagan, R., Barbosa-Canovas, G.V., Swanson, B.G., 2001. EngineeringAspects of the Continuous Treatment of Fluid Foods by Pulsed Electric Fields.Pulsed Electric Fields in Food Processing. Technomic Publishing CompanyPress.

Evrendilek, G.A., Zhang, Q.H., 2005. Effects of pulse polarity and pulse delaying timeon pulsed electric fields-induced pasteurization of E. coli O157:H7. Journal of Food Engineering 68 (2), 271–276.

Fang, J.L., Piao, Z.L., Zhang, X.H., 2006. Study on high-voltage pulsed electric fieldssterilization mechanism experiment. The Journal of American Science 2 (2), 39–43.

Floury, J., Grosset, N., Lesne, E., Jeantet, R., 2006. Continuous processing of skim milkby a combination of pulsed electric fields and conventional heat treatments:does a synergetic effect on microbial inactivation exist? Lait 86, 203–211.

Fox, M.B., Esveld, D.C., Boom, R.M., 2007. Conceptual design of a mass parallelizedPEF microreactor. Trends in Food and Technology 18, 484–491.

Gallagher, T.J., Pearmain, A.J., 1983. High Voltage: Measurement, Testing andDesign. John Wiley and Sons, Chichester.

Garcia, D., Gomez, N., Raso, J., Pagan, R., 2005. Bacterial resistance after pulsedelectric fields depending on the treatment medium pH. Innovative Food Scienceand Engineering Technologies 6 (4), 388–395.

Ge, S.H., 2005. The application of high-voltage pulse electric field in foodsterilization. Physics and Engineering 15 (1), 42–44.

Geren, D.K., 1984. Sterilization Apparatus. US Patent 4,457,221.Gongora-Nieto, M.M., Pedrow, P.D., Swanson, B.G., Barbosa-Canovas, G.V., 2003.Impact of air bubbles in a dielectric liquid when subjected to high fieldstrengths. Innovative Food Science and Emerging Technologies 4 (1), 57–67.

Grahl, T., Markl, H., 1996. Killing of micro-organisms by pulsed electric field.Applied Microbiology and Biotechnology 45, 148–157.

Heinz, V., Knorr, D., 2000. Effect of pH, ethanol addition and high hydrostaticpressure on the inactivation of Bacillus subtilis by pulsed electric fields.Innovative Food Science and Emerging Technologies 1 (2), 151–159.

Heinz, V., Toepfl, S., Knorr, D., 2003. Impact of temperature on lethality and energyefficiency of apple juice pasteurizations by pulsed electric fields treatment.Innovative Food Science and Emerging Technologies 4 (2), 167–175.

Hofmann, G.A., 1984. Microflora Reduction in Liquids with Pulsed Electric Fields.Internal Technical Report. Biotechnologies and Experimental Research Inc., SanDiego.

Hofmann, G.A., 1989. Cells in electric fields, physical and practical electronic aspectsof electro-cell fusion and electroporation. In: Neuman, E., Sowers, A.E., Jordan,C.A. (Eds.), Electroporation and Electrofusion in Cell Biology. Plenum Press.

Hoover, D.G., 1997. Minimally processed fruits and vegetables: reducing microbial

load by nonthermal physical treatments. Food Technology 51 (6), 66–71.

Hulsheger, H., Niemann, E.G., 1980. Lethal effects of high voltage pulses on E. coliK12. Radiation and Environmental Biophysics 18 (4), 281–288.

Hulsheger, H., Pottel, J., Niemann, E., 1981. Killing of bacteria with electric pulses of high fields strength. Radiation and Environment Biophysics 20 (1), 53–65.

Innings, F., 1998. Personal communication. TetraPak Processing, Lund, Sweden. Jayaram, S., Castle, G.S.P., Margaritis, A., 1992. Kinetics of sterilization of

Lactobacillus brevis cells by the application of high voltage pulses.Biotechnology and Bioengineering 4 (11), 1412–1420.

John, J.H., Ziebland, S., Yudkin, P., Roe, L.S., Neil, H.A.W., 2002. Effects of fruit andvegetable consumption on plasma antioxidant concentrations and blood

pressure: a randomized controlled trial. The Lancet 359 (9322), 1969–1974.Kempkes, M., Gaudreau, M., Hawkey, T., Petry, J., 2008. Scaleup of PEF systems for

food and waste streams. In: Pulsed Power Conference 2007, 16th IEEEInternational, vol. 2. pp. 1064–1067..

Knorr, D., Geulen, M., Grahl, T., Sitzman, W., 1994. Food application of high electricfield pulses. Trends in Food Science and Technology 5 (3), 71–75.

Lado, B.H., Yousef, A.E., 2002. Alternative food-preservation technologies: efficacyand mechanisms. Microbes and Infection 4 (4), 433–440.

Lebovka, N.I., Praporscic, I., Vorobiev, E., 2004. Combined treatment of apples bypulsed electric fields and by heating at moderate temperature. Journal of FoodEngineering 65 (2), 211–217.

Martin, O., Qin, B.L., Chang, F.J., Barbosa-Canovas, G.V., Swanson, B.G., 1997.Inactivation of Escherichia coli in skim milk by high intensity pulsed electricfields. Journal of Food Process Engineering 20 (4), 317–336.

Mastwijk, H.C., Bartels, P.V., 2001. Integrated Modular Design of a Pulsed ElectricalField Treatment Chamber. US Patent 6,178,880.

Matsumoto, Y., Shioji, N., Satake, T., Sakuma, A., 1991. Inactivation of microorganisms by pulsed high voltage application. Industry ApplicationsSociety Annual Meeting, pp. 652–659.

McCall, M.R., Frei, B., 1999. Can antioxidant vitamins materially reduce oxidativedamage in humans? Free Radical Biology and Medicine 26 (7–8), 1034–1053.

McDonald, C.J., Lloyd, S.W., Vitale, M.A., Petersson, K., Innings, F., 2000. Effects of pulsed electric fields on microorganisms in orange juice using electric fieldstrengths of 30 and 50 kV/cm. Journal of Food Science 65 (6), 984–989.

Mertens, B., Knorr, D., 1992. Developments of nonthermal processes for foodpreservation. Food technology 46 (5), 124–133.

Min, S., Evrendilek, G.A., Zhang, H.Q., 2007. Pulsed electric fields: processing system,microbial and enzyme inhibition, and shelf life extension of foods. IEEETransactions on Plasma Science 35 (1), 59–73.

Misaki, T., Tsuboi, H., Itaka, K., Hara, T., 1982. Computation of three-dimensionalelectric field problems by a surface charge method and its application tooptimum insulator design. IEEE Transactions on Power Apparatus and Systems101 (3), 627–634.

Morshuis, P.H.F., Van Den Bosch, H.F.M., De Haan, S.W.H., Ferreira, J.A., 2002.Treatment Apparatus Method for Preserving Pumpable Food Products in aPulsed Electric Field. US Patent 6,393,975.

Narsetti, R., Curry, R.D., McDonald, K.F., Clevenger, T.E., Nichols, L.M., 2006.

Microbial inactivation in water using pulsed electric fields and magneticpulse compressor technology. IEEE Transaction on Plasma Science 34 (4), 1386–1393.

Odriozola-Serrano, I., Bendicho-Porta, S., Martin-Belloso, O., 2006. Comparativestudy on shelf life of whole milk processed by high-intensity pulsed electricfield or heat treatment. American Dairy Science Association, vol. 89. pp. 905–911.

Ortega-Rivas, E., Zarate-Rodriguez, E., Barbosa-Canovas, G.V., 1998. Apple juicepasteurization using ultrafiltration and pulsed electric fields. Institution of Chemical Engineers 76, 193–198.

Pizzichemi, M., Occhialini, P.D.G., 2007. Application of pulsed electric fields to foodtreatment. Nuclear Physics B – Proceeding Supplements 172, 314–316.

Pothakamury, U.K., Vega, H., Zhang, Q., Barbosa-Canovas, G.V., Swanson, B.G., 1996.Effect of growth stage and processing temperature on the inactivation of E.Coliby pulsed electric fields. Journal of Food Protection 59 (11), 1167–1171.

Qin, B.L., Barbosa-Canovas, G.V., Swanson, B.G., Pedrow, P.D., Olsen, R.G., 1998.Inactivation microorganisms using a pulsed electric field continuous treatmentsystem. IEEE Transactions on Industry Applications 34 (1), 43–50.

Qin, B.L., Barbosa-Canovas, G.V., Swanson, B.G., Pedrow, P.D., Olsen, R.G., Zhang,

Q.H., 1997. Continuous flow electrical treatment of flowable food products. USPatent 5,662,031.

Qin, B.L., Barbosa-Canovas, G.V., Swanson, B.G., Pedrow, P.D., Olsen, R.G., Zhang,Q.H., 2000. Continuous Flow Electrical Treatment of Flowable Food Products. USPatent 6,019,031.

Qin, B.L., Chang, F.J., Barbosa-Canovas, G.V., Swanson, B.G., 1995. Nonthermalinactivation of Saccharomyces cerevisiae in apple juice using pulsed electricfields. Food Science and Technology 28 (6), 564–568.

Qin, B.L., Zhang, Q.H., Barbosa-Canovas, G.V., Swanson, B.G., Pedrow, P.D., 1994.Inactivation of microorganism by pulsed electric fields of different voltagewaveforms. IEEE Transactions on Dielectrics and Electrical Insulation 1 (6),1047–1057.

Ramaswamy, R., Jin, T., Balasubramaniam, V.M., Zhang, H., 2005. Pulsed electric fieldprocessing: fact sheet for food processors. Meeting Abstract..

Reina, L.D., Jin, Z.T., Zhang, Q.H., 1998. Inactivation of Listeria monocytogenes in milkby pulsed electric field. Journal of Food Protection 61 (9), 1203–1206.

Ruhlman, K.T., Jin, Z.T., Zhang, Q.H., 2001. Physical properties of liquid foods forpulsed electric field treatment. In: Barbosa-Canovas, G.V., Zhang, Q.H., Tabilo-

Munizaga, G. (Eds.), Pulsed Electric Field in Food Processing: FundamentalAspects and Application. Technomic, PA, pp. 45–56.


ARTICLE IN PRESS







Sale, A.J.H., Hamilton, W.A., 1967a. Effects of high electric fields on microorganisms:I. Killing of bacteria and yeasts. Biochimica et Biophysica Acta 148 (3), 781–788.

Sale, A.J.H., Hamilton, W.A., 1967b. Effects of high electric fields on microorganisms:II. Mechanism of action of the lethal effect. Biochimica et Biophysica Acta 148(3), 789–800.

Sanchez-Moreno, C., Plaza, L., de Ancos, B., Cano, M.P., 2003. Quantitative bioactivecompounds assessment and their relative contribution to the antioxidantcapacity of commercial orange juice. Journal of the Science of Food andAgriculture 83 (5), 430–439.

Schoenbach, K.H., Joshi, R.P., Stark, R.H., Dobbs, F.C., Beebe, S.J., 2000. Bacterialdecontamination of liquids with pulsed electric fields. IEEE Transaction onDielectrics and Electrical Insulation 7 (5), 637–645.

Sensoy, I., Zhang, Q.H., Sastry, S.K., 1997. Inactivation kinetics of Salmonella dublinby pulsed electric field. Journal of Food Process Engineering 20 (5), 367–381.

Sepulveda, D.R., Gongora-Nieto, M.M., San-Martin, M.F., Barbosa-Canovas, G.V.,2005. Influence of treatment temperature on the inactivation of Listeria innocuaby pulsed electric fields. Lebensmittel-Wissenschaft und – Technologie 38 (2),167–172.

Torregrosa, F., Esteve, M.J., Frigola, A., Cortes, C., 2006. Ascorbic acid stability duringrefrigerated storage of orange–carrot juice treated by high pulsed electric fieldand comparison with pasteurized juice. Journal of Food Engineering 73 (4),339–345.

Vega-Mercado, H., Pothamury, U.R., Chang, F.J., Barbosa-Canovas, G.V., Swanson,B.G., 1996. Inactivation of Escherichia coli by combining pH, ionic strength andpulsed electric fields hurdles. Food Research International 29 (2), 117–121.

Williamson, G., 1996. Protective effects of fruits and vegetables in the diet. Nutritionand Food Science 1, 6–10.

Wouters, P.C., Bos, A.P., Uecket, J., 2001. Membrane permeabilization in relation toinactivation kinetics of Lactobacillus species due to pulsed electric fields.Applied and Environmental Microbiology 67 (7), 3092–3101.

Wu, Y., Mittal, G.S., Griffiths, M.W., 2005. Effect of pulsed electric field on theinactivation of microorganisms in grape juice with and without antimicrobials.

Biosystems Engineering 90 (1), 1–7.Yeom, H.W., Streaker, C.B., Zhang, Q.H., Min, D.B., 2000. Effects of pulsed electric

fields on the quality of orange juice and comparison with heat pasteurization. Journal of Agricultural and Food Chemistry 48 (10), 4597–4605.

Yin, Y.G., Zhang, Q.H., Sastry, S.K., 1997. High Voltage Pulsed Electric FieldTreatment Chamber for the Preservation of Liquid Food Products. US Patent5,690,978.

Zhang, X.H., 2005. Pulsed electric fields sterilization mechanism and experimentalequipment research. The Engineering College of the Northeast AgriculturalUniversity, Harbin.

Zhang, Q.H., Barbosa-Canovas, G.V., Swanson, B.G., 1995. Engineering aspects of pulsed electric field pasteurization. Journal of Food Engineering 25 (2), 261–281.


ARTICLE IN PRESS

lagi pasteurisasi

Documents