Pulse Electric Field-Assisted Extraction

Full text

Enhancing Extraction
Processes in the
Food Industry
Edited by
Nikolai Lebovka
Eugene Vorobiev
Farid Chemat

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v
Contents
List of Figures ..........................................................................................................vii
List of Tables ..........................................................................................................xvii
Series Preface ..........................................................................................................xxi
Preface.................................................................................................................. xxiii
Acknowledgments ..................................................................................................xxv
Series Editor .........................................................................................................xxvii
Editors ...................................................................................................................xxix
Contributors ..........................................................................................................xxxi
Abbreviations .......................................................................................................xxxv
Chapter 1 Introduction to Extraction in Food Processing ....................................1
Philip J. Lloyd and Jessy van Wyk
Chapter 2 Pulse Electric Field-Assisted Extraction ............................................25
Eugene Vorobiev and Nikolai I. Lebovka
Chapter 3 Microwave-Assisted Extraction .........................................................85
María Dolores Luque de Castro and Feliciano Priego-Capote
Chapter 4 Ultrasonically Assisted Diffusion Processes ...................................123
Zbigniew J. Dolatowski and Dariusz M. Stasiak
Chapter 5 Pulsed Electrical Discharges: Principles and Application to
Extraction of Biocompounds ........................................................... 145
Nadia Boussetta, Thierry Reess, EugeneVorobiev, and
Jean- Louis Lanoisellé
Chapter 6 Combined Extraction Techniques .................................................... 173
Farid Chemat and Giancarlo Cravotto
Chapter 7 Supercritical Fluid Extraction in Food Processing .......................... 195
Rakesh K. Singh and Ramesh Y. Avula
Chapter 8 Pressurized Hot Water Extraction and Processing ...........................223
Charlotta Turner and Elena Ibañez

vi Contents
Chapter 9 Instant Controlled Pressure Drop Technology in Plant
Extraction Processes ........................................................................255
Karim Salim Allaf, Colette Besombes, Baya Berka,
MagdalenaKristiawan, Vaclav Sobolik, and
TamaraSabrineVicenta Allaf
Chapter 10 High Pressure–Assisted Extraction: Method, Technique, and
Application .......................................................................................303
Krishna Murthy Nagendra Prasad, AminIsmail, John Shi, and
Yue Ming Jiang
Chapter 11 Extrusion-Assisted Extraction: Alginate Extraction from
Macroalgae by Extrusion Process ....................................................323
Peggy Vauchel, Abdellah Arhaliass, JackLegrand,
RégisBaron,
and Raymond Kaas
Chapter 12 Gas-Assisted Mechanical Expression of Oilseeds ........................... 341
Paul Willems and André B. de Haan
Chapter 13 Mechanochemically Assisted Extraction ......................................... 361
Oleg I. Lomovsky and Igor O. Lomovsky
Chapter 14 Reverse Micellar Extraction of Bioactive Compounds for
FoodProducts ...................................................................................399
A. B. Hemavathi, H. Umesh Hebbar, and
KarumanchiS.M.S.Raghavarao
Chapter 15 Aqueous Two-Phase Extraction of Enzymes for Food Processing ........437
M. C. Madhusudhan, M. C. Lakshmi, and
KarumanchiS.M.S.Raghavarao
Chapter 16 Enzyme-Assisted Aqueous Extraction of Oilseeds .......................... 477
Stephanie Jung, JulianaMariaLeiteNobrega de Moura,
KerryAlan Campbell, and Lawrence A. Johnson

25
2
Pulse Electric Field-
Assisted Extraction
Eugene Vorobiev and Nikolai I. Lebovka
CONTENTS
2.1 Introduction ....................................................................................................26
2.2 PEF-Induced Effects .......................................................................................28
2.2.1 Basics of Electroporation ....................................................................28
2.2.1.1 Transmembrane Potential ....................................................28
2.2.1.2 Effects of Cell Size and Electrical Conductivity Contrast...29
2.2.1.3 Resealing of Cells and Mass Transfer Process .................... 31
2.2.2 Quantication of PEF-Induced Disintegration ...................................32
2.2.2.1 Microscopic Study ...............................................................32
2.2.2.2 Electrical Conductivity ........................................................32
2.2.2.3 Diffusion Coefcient ...........................................................34
2.2.2.4 Textural Characteristics .......................................................34
2.2.2.5 Acoustic Measurements .......................................................35
2.2.2.6 Correlations between Z Values Estimated by Different
Techniques ...........................................................................36
2.2.3 Kinetics of Damage ............................................................................36
2.2.3.1 Characteristic Damage Time ..............................................38
2.2.3.2 Synergy of Simultaneous Electrical and Thermal
Treatments ............................................................................38
2.2.4 Inuence of Pulse Control ..................................................................40
2.2.4.1 Waveforms of PEF Pulses ....................................................40
2.2.4.2 Pause between Pulses........................................................... 41
2.2.4.3 Pulse Duration ..................................................................... 42
2.2.5 Power Consumption ............................................................................42
2.3 PEF-Assisted Extraction .................................................................................45
2.3.1 Vegetable and Fruit Tissues ............................................................... 45
2.3.1.1 Potato ...................................................................................45
2.3.1.2 Sugar Beet ............................................................................46
2.3.1.3 Sugar Cane ...........................................................................50
2.3.1.4 Red Beet ...............................................................................50
2.3.1.5 Carrot ................................................................................... 51
2.3.1.6 Apple .................................................................................... 52
2.3.1.7 Grapes ..................................................................................55

26 Enhancing Extraction Processes in the Food Industry
2.1 INTRODUCTION
Pulsed electric elds (PEFs) are now attracting strong interest in food engineering
research. This minimally invasive method allows avoidance of undesirable changes
in a biological material, which are typical for other techniques such as thermal,
chemical, and enzymatic ones (Knorr et al. 2001; Vorobiev et al. 2005; Toep et al.
2005; Vorobiev and Lebovka 2006, 2008, 2010; Toep and Knorr 2006; Raso and
Heinz 2006; Toep et al. 2007a,b; Ravishankar 2008; Donsì et al. 2010; Lebovka and
Vorobiev 2010; Sack et al. 2010; Toep and Heinz 2010). A supplementary advan-
tage of PEF treatment for food applications is its potential to kill microorganisms
(Barbosa-Cánovas et al. 1998, 2000; Barbosa-Cánovas and Cano 2004; Altunakar et
al. 2007; Vega-Mercado et al. 2007; Tewari and Juneja 2007).
Many useful examples of PEF application for enhancing pressing, drying, extrac-
tion, and diffusion in the processing of materials of biological origin have already
been demonstrated (Figure 2.1). PEF-assisted techniques display unusual synergetic
2.3.1.8 Oil- and Fat-Rich Plants .......................................................55
2.3.1.9 Other Vegetable and Fruit Tissues .......................................56
2.3.2 Biosuspensions ....................................................................................57
2.3.2.1 Cell Disruption Techniques .................................................57
2.3.2.2 PEF Application for Killing and Disruption of
Microorganisms ...................................................................58
2.3.2.3 Yeasts ...................................................................................59
2.3.2.4 Escherichia coli ...................................................................60
2.4 PEF Pilot-Scale Experiments and Applications ............................................. 62
2.4.1 Some Examples of Related Recent Patents ........................................62
2.4.2 Pasteurization and Regulation of Microbial Stability ........................62
2.4.3 Extraction ............................................................................................64
2.4.4 Food Safety Aspects ...........................................................................67
2.5 Conclusions ..................................................................................................... 67
Acknowledgments ....................................................................................................67
References ................................................................................................................67
PEF
Cell
Selective
extraction
Drying
Pressing
Diffusion
Freezing
Osmotic
treatment
FIGURE 2.1 The PEF-assisted technique.

27Pulse Electric Field-Assisted Extraction
effects and present the possibility of “cold diffusion,” “cold drying,” and improved
osmotic and freezing treatment.
The PEF technology is not simple in application, and has a long history. The main
historical landmarks in the eld are summarized in Table 2.1. The most important
of them are the discovery of bioelectricity by Luigi Galvani in 1791 and the dis-
covery of electroporation in the 1960s–1970s (see, e.g., Weaver and Chizmadzhev
1996; Pavlin et al. 2008; Pakhomov et al. 2010; Saulis 2010). Many efforts were
also aimed at industrial implementations of alternative current (AC), direct current
(DC), and PEF treatments. They started at the beginning of the past century by
application of the said methods for microbial killing, canning, ohmic heating, and
others (Stone 1909; Beattie 1914; Anderson and Finkelshtein 1919; Prescott 1927;
Fettermann 1928; Getchell 1935). Different electrical apparatus for treatment of uid
foods were patented (Jones 1897; Anglim 1923; Ball 1937). Later on, Flaumenbaum
(1949) and Zagorulko (1958) reported applications of DC and AC electric elds for
treatment of prunes, apples, grapes, and sugar beets. They demonstrated acceleration
of extraction by electrical breakage of cellular membranes. This phenomenon was
called electroplasmolysis.
TABLE 2.1
Main Historical Landmarks in the Progress of PEF Applications
Development Authors and Data Comment
Discovery of bioelectricity Luigi Galvani (1791)
Microbial killing Prochownick and Spaeth (1890) DC and AC
Different practical applications of DC and AC
for microbial killing and ohmic heating
Different authors (1900–1940); for
a review, see, e.g., de Alwis and
Fryer (1990)
DC and AC
Increase in juice yield from fruits Flaumenbaum (1949) (220 V, 50 Hz)
Electroplasmolysis, extraction of juice from
sugar beets
Zagorulko (1958) DC and AC
Electrophysiological model of biotissues,
derivation of transmembrane potential
Schwan (1957), Foster and Schwan
(1989)
Disintegration of biomaterials, killing of
bacteria
Doevenspeck (1961), Sale and
Hamilton (1967)
PEF
Reversible electrical breakdown of
biomembranes, discovery of electroporation
Stampi (1958), Neumann and
Rosenheck (1972)
PEF
Earlier industrial applications (canning and
wine production; treatment of apples, sugar
beets, etc.)
Different authors (1965–1980); for
a review, see Rogov and Gorbatov
(1974)
DC and AC
Current applications of PEF for microbial
killing and disintegration of plant tissues
Different authors (1965–1980); for
a review, see Vorobiev and
Lebovka (2010), Donsì et al.
(2010), Lebovka and Vorobiev
(2010), Sack et al. (2010),
Barbosa-Cánovas and Cano
(2004), Jaeger and Knorr (2010)
PEF

28 Enhancing Extraction Processes in the Food Industry
The most important steps were made in the 1960s–1970s when the rst applica-
tions of PEF were reported (Doevenspeck 1961; Sale and Hamilton 1967), the rst
industrial AC setups were implemented (Flaumenbaum 1968; Kogan 1968; Matov
and Reshetko 1968; Rogov and Gorbatov 1974, 1988), and the concept of membrane
electroporation was theoretically worked out (Weaver and Chizmadzhev 1996;
Pavlin et al. 2008; Pakhomov et al. 2010; Saulis 2010).
Starting from the early 1990s, many new practical PEF-assisted techniques have
been tested, and their usability for microbial killing, food preservation, and accelera-
tion of drying, pressing, diffusion, and selective extraction has been demonstrated
(Gulyi et al. 1994; Knorr et al. 1994; Toep et al. 2007a; Ravishankar et al. 2008;
Vorobiev and Lebovka 2008). Since then, new types of higher-voltage PEF genera-
tors, new designs of treatment chambers, and new pilot schemes have been devel-
oped (Barbosa-Cánovas et al. 1998; Vorobiev and Lebovka 2008).
This chapter reviews the current state of the art in food engineering, existing
fundamental knowledge on the mechanism of PEF-induced effects in biomaterials,
impact of PEF on functional food ingredients, recent experiments in the eld, practi-
cal applications of PEF and their examples for different food materials, and perspec-
tives on the industrial applications of PEF-assisted extraction techniques.
2.2 PEF-INDUCED EFFECTS
2.2.1 Basics of ElEctroporation
The impact of PEF on biomaterials is reected by the loss of membrane barrier func-
tions. A membrane envelope around the cell restricts the exchange of inter- and intra-
cellular media. The application of an electric eld induces the formation of pores
inside the membrane and increases its permeability. Traditionally this phenomenon
is called “electroporation” or “electropermeabilization” (Weaver and Chizmadzhev
1996; Pakhomov et al. 2010).
2.2.1.1 Transmembrane Potential
The degree of electroporation depends on the potential difference across a mem-
brane, or the transmembrane potential, u
m
. Electroporation requires some threshold
value of u
m
, typically 0.5–1.5 V. Depending on treatment conditions, the value of u
m
,
and PEF exposure time (t
PEF
), a temporary (reversible) or irreversible loss of barrier
function may occur. It is assumed that electroporation involves membrane charging,
membrane polarization (charging time t
c
> 1 μs), expansion of pore radii, and aggre-
gation of pores (during the rst 100 μs). On turning off the electric eld, pore reseal-
ing and memory effects (lasting from seconds to hours) may be observed (Teissié et
al. 2005; Pavlin et al. 2008). A number of theoretical models have been proposed
for the description of the electroporation of membranes at the micro level. These
theories considered different mechanisms, such as electromechanical, electrohydro-
dynamic, electroosmotic, and the development of viscoelastic instabilities. However,
the mechanism of membrane electroporation is not yet fully understood, and there
are a lot of discrepancies between theoretical and experimental results (Weaver and
Chizmadzhev 1996; Pakhomov et al. 2010).

29Pulse Electric Field-Assisted Extraction
For a spherical cell in the external eld, the induced transmembrane potential
u
m
is a function of the cell radius R, eld strength E, and position of the observation
point on the surface of a membrane (Schwan 1957):
u
m
= 1.5REe cos θ(1 – exp(–t/τ
C
)) (2.1)
Here θ is the angle between the external eld E and radius vector R, e is the electro-
poration factor that is dependent on geometry and electrophysical properties of cells,
and τ
C
(≈1–10 μs) is the time constant reecting the process of charging the mem-
brane capacity C (Figure 2.2) (Pavlin et al. 2008). Note that for anisotropic cells, the
value of u
m
is a function not only of electric eld intensity and cell size but also of
the cell shape and orientation.
2.2.1.2 Effects of Cell Size and Electrical Conductivity Contrast
The value of u
m
is directly proportional to the cell radius R, while the drop of poten-
tial is highest at the cell poles and decreases toward zero at θ = ±π/2. Thus, larger
cells become damaged before smaller ones, and the probability of damage is at max-
imum at the cell poles.
Typically the width of membrane d (≈5 nm) is very small as compared with the
cell radius R (R ≈ 50 μm for plant cells and R < 10 μm for microbial cells). The
electric eld strength inside the membranes can be estimated as E
m
= u
m
/d ≈ ER/d ~
10
4
E. The experimentally estimated threshold value E
t
required for a noticeable elec-
troporation is of the order of 100 V/cm for plant cells (Vorobiev and Lebovka 2006)
and 10 kV/cm for small microbial cells (R ≈ 1–10 μm) (Barbosa-Cánovas et al. 1998).
In practice, the degree of electropermeabilization also depends on the properties of
materials and details of the pulse protocol (Vorobiev and Lebovka 2006). A consid-
erable damage to plant tissues can be observed at E = 500–1000 V/cm and treatment
+
−
σ
d
σ
E
Cell
2C
2C
2R
Electrode
Electrode
r
σ
m
θ
FIGURE 2.2 Electrophysical schema of a cell. Here R is the radius of the cell; d is the mem-
brane width; θ is the angle between the external eld E and radius vector r at the surface of
membrane; C is the membrane capacitance; and σ
m
, σ, and σ
d
are the electrical conductivities
of the membrane, extracellular medium, and cytoplasm, respectively.

30 Enhancing Extraction Processes in the Food Industry
time within 10
−4
–10
−1
s. For microbial killing, higher eld strengths (E = 20–50 kV/
cm) and shorter treatment times (10
−5
–10
−4
s) are required.
The general expression for electroporation factor e is rather complex (Kotnik et
al. 1998)
e = (3d/R)σ
d
σ/[(σ
m
+ 2σ)(σ
m
+ 0.5σ
d
) – (1 – 3d/R)(σ – σ
m
)(σ
d
– σ
m
)] (2.2)
where d is the membrane width (≈5 nm) and σ
m
, σ, and σ
d
are the electrical conduc-
tivities of the membrane, external medium, and cytoplasm, respectively.
At σ
m
<< σ, σ
m
<< σ
d
, Equation 2.2 reduces to e ≈ 1. This approximation works
well for suspensions of small biological cells, where the typical electrical conduc-
tivity values are σ
m
= 3 ×
10
–7
S/m and σ
d
= 0.3 S/m (Pavlin et al. 2008). Figure 2.1
shows that at σ
m
= 3 × 10
–7
S/m, the value of e is an increasing function of σ/σ
d
, which
approaches 1 at σ/σ
d
> 0.2.
The σ
m
value of a plant cell is unknown; however, it can be estimated from the
conductivities of intact (σ = σ
i
when all membranes are intact) and completely dam-
aged (σ ≈ σ
d
when all membranes are disrupted) plant tissues. For the serial model of
cell packing, one can obtain (d + R)/σ
i
= /σ
m
+R/σ
d
and
σ
m
≈ σ
i
(d/R)k/(k – 1) (2.3)
where k = σ
d
/σ
i
is the electrical conductivity contrast.
The typical values of σ
i
and k for different fruit and vegetable tissues (Bazhal et
al. 2003a) are presented in Table 2.2. At σ
i
≈ 0.02–0.08 S/m, R = 50 μm, and k >>1,
the membrane conductivities of plant tissues may be estimated as σ
m
≈ σ
i
(d/R) ≈
2–8.10
–6
S/m.
TABLE 2.2
Tissue Characteristics for Different Fruits and Vegetables, Measured at a
Temperature (T) of 293 K and a Frequency (f) of 1 kHz
Material Cell Radius, R (μm) Intact Conductivity, σ
i
(S/m) Contrast, k =σ
d
/σ
i
Apple 35 ± 5 0.022 ± 0.007 10 ± 3
Banana 39 ± 13 0.082 ± 0.018 5.4 ± 0.9
Aubergine – 0.051 ± 0.009 –
Carrot 30 ± 3 0.059 ± 0.019 4.5 ± 0.6
Courgette 30 ± 4 0.029 ± 0.009 11.9 ± 3.1
Cucumber – 0.032 ± 0.005 –
Potato 47 ± 6 0.044 ± 0.014 13 ± 3
Pear – 0.032 ± 0.005 –
Orange 59 ± 9 0.063 ± 0.009 1.26 ± 0.23
Source: Lebovka, N.I. et al., Innov Food Sci Emerg, 2, 113, 2001; Bazhal, M. et al., Biosyst Eng, 86, 339,
2003; and Ben Ammar, J. et al., J Food Sci, 76, E90, 2011.
Note: The presented data correspond mean ± SD.

31Pulse Electric Field-Assisted Extraction
Note that for plant tissues, the electroporation factor e can be noticeably smaller
than 1 and be dependent on the contrast ratio k (Figure 2.3). Thus, it can be expected
that the threshold electric eld strength value E
t
, required for noticeable electro-
poration, will be high for plant tissues with small electrical conductivity contrast
k and small electroporation factor e. This conclusion was recently supported by a
comparison of electroporation efciency for fruit and vegetable tissues with different
conductivity contrasts (Ben Ammar et al. 2011).
2.2.1.3 Resealing of Cells and Mass Transfer Process
Lebovka et al. (2000, 2001) have put forward a hypothesis explaining how PEF treat-
ment affects the structure of cellular tissues. They considered the PEF effect as a
correlated percolation that is governed by two processes: (i) resealing of cellsand
(ii)moisture mass transfer inside the cellular structure, which is sensitive to PEF
treatment repetitions. At a low enough electric eld intensity, electroporation is
reversible as far as the resealing process is quick enough to repair the membranes
immediately after the termination of PEF treatment. At moderate PEF treatment,
some of the cells lose their permeability, but others may reseal (Lebovka et al. 2001).
It was demonstrated that the insulating properties of the cell membrane (e.g., in
potato, apple, and sh tissues) can be recovered within several seconds after pulse
termination (Angersbach et al. 2000). The reversible permeabilization of potato cells
was conrmed by transient changes in the viscoelastic properties after PEF appli-
cation with a single 10
–5
, 10
–4
, or 10
–3
s rectangular pulse at electric eld strength
E ranging from 30 to 500 V/cm (Pereira et al. 2009). According to calorimetric
data, PEF application resulted in a strong metabolic response of potato tissue depen-
dent on the pulsing conditions (Galindo et al. 2008a,b,c; Galindo et al. 2009a,b).
The PEF-specic metabolic responses 24 h after the application of PEF (one 1 ms
1
1
8
k = 10
5
3
2
1.5
0.8
0.6
0.4
0.2
Electroporation factor (e)
0 0.2
Ratio of conductivities (σ/σ
d
)
0.4 0.6 0.8 1
FIGURE 2.3 Electroporation factor e versus σ/σ
i
(Equation 2.2). The curves, k = σ
d
/σ
i
, were
obtained from Equations 2.2 through 2.3 at R = 50 μm (for plant tissues). Curve 1 was calcu-
lated for σ
m
= 3 ×
10
–7
S/m, σ
d
= 0.3 S/m, and R = 5 μm (for microbial cell).

32 Enhancing Extraction Processes in the Food Industry
rectangular pulse at E = 30–500 V/cm) may involve degradation of starch and ascor-
bic acid (Galindo et al. 2008b). High-intensity PEF treatment causes an irreversible
damage to the cell membrane. Long-term changes in conductivity after the applica-
tion of PEF treatment can also be related to osmotic ow and moisture redistribution
inside the sample (Lebovka et al. 2001).
2.2.2 Quantification of pEf-inducEd disintEgration
The damage degree Z can be dened as the volume fraction of the damaged cells.
However, the experimental determination of Z and quantication of PEF-induced
disintegration is not an easy task, although many experimental techniques have been
tested thus far.
2.2.2.1 Microscopic Study
Optical microscopy was used for the study of PEF-treated aqueous suspensions of
Chinese hamster ovary cells (Valic et al. 2003). Microscopic observations evidenced
that the degree of electropermeabilization may be dependent on the anisotropy of
cells. Visual observations evidenced that elongated cells became electroperme abilized
more intensively when the longest axis of the cell was parallel to the electric eld. The
same conclusion was reached for apple tissues. It was shown that lower electric elds
were required for permeabilization of anisotropic apple cells when the electric eld
was applied parallel to the longest axes of the cells (Chalermchat et al. 2010).
Optical microscopy was used for in situ visualization of PEF-induced color
changes in onion epidermis stained with neutral red (Fincan and Dejmek 2002).
The nal electrical conductivity increase was directly proportional to the number
of permeabilized cells. Microscopic studies showed that intact cell architecture was
preserved, while membrane damage was conrmed by free colorant diffusion inside
electroporated cells. Thus, these experiments evidenced that PEF did not noticeably
affect the structure of cell walls. This important conclusion was supported by scan-
ning electron microscope images, where a similarity in cell wall structure, and area
and morphology of starch granules between untreated and PEF-treated potato tissues
was observed (Ben Ammar et al. 2010).
Microscopic observation is the most direct way for the visual determination of
the fraction of damaged cells, Z. However, the application of this method for estima-
tion of Z in plants is not simple, accounting for the difculties related with sample
preparation, pH sensitivity of the method, and conductivity of the solution used in
mounting the epidermis. That is why this method is not widely used for characteriza-
tion of PEF-induced damage in plant tissues.
2.2.2.2 Electrical Conductivity
The simplest way for characterization of Z is based on electrical conductivity mea-
surements, because the average electrical conductivity of a tissue increases with the
degree of its damage. The electrical conductivity disintegration index seems Z
C
can
be dened as (Rogov and Gorbatov 1974; Lebovka et al. 2002)
Z
C
= (σ – σ
i
)/(σ
d
– σ
i
) (2.4)

33Pulse Electric Field-Assisted Extraction
where σ is the electrical conductivity value measured at low frequency (≈1 kHz),
and indexes i and d refer to the conductivities of intact and totally damaged tissue,
respectively. This equation gives Z
C
= 0 for the intact tissue and Z
C
= 1 for the totally
disintegrated material.
The procedure is simple and can be easily applied for continuous monitoring of
the damage degree during PEF treatment (Figure 2.4). This method requires knowl-
edge of the value of σ
d
. This value can be estimated by measurement of the electrical
conductivity of the freeze–thawed tissue. Another way to estimate σ
d
is based on
PEF treatment at high electric eld strengths (E ≈ 1000 V/cm) and long treatment
durations (t
PEF
≈ 0.1–1 s) (Bazhal et al. 2003a; Lebovka et al. 2004a). However, the
value of σ
d
determined in such a way is not well dened because freeze–thawing or
strong PEF treatment can affect the structure of cell walls and inuence σ
d
.
Other methods are based on electrical conductivity measurements at low and high
frequencies, and assume validity of some bioimpedance models for plant tissues
(Angersbach et al. 2002; Pliquett 2010). For example, the conductivity disintegration
index Z can be estimated as (Angersbach et al. 2002)
Z
C i i i
/= − −
∞
( ) ( )ασ σ σ σ
0 0 0
(2.5)
where
α σ σ=
∞ ∞
i
/
and the indexes 0 and ∞ refer to the low (≈1 kHz) and high (3–50
MHz) frequency conductivity limits, respectively (Figure 2.4b).
However, any method based on electrical conductivity should be applied with
caution (Pliquett 2010). The electrical conductivity of tissues is sensitive to the spa-
tial redistribution of air and moisture content inside the tissue, membrane reseal-
ing, and other factors (Lebovka et al. 2001). As a result, the transient behavior of
Frequency ( f )
PEF treatment time (t
PEF
)
0
(a)
(b)
Electrical conductivity (σ)
σσ
σ
i
σ
i
0
ασ
0
– σ
i
0
σ
– σ
i
Z
C
= (σ
– σ
i
)/(σ
d
– σ
i
)
Z
C
= (ασ
0
– σ
i
)/(σ
i
∞
– σ
i
0
)
= α
σ
i
∞
– σ
i
0
σ
d
– σ
i
σ
d
σ
i
∞
σ
i
∞
σ
∞
σ
∞
∞
∞
σ
0
FIGURE 2.4 Estimation of electrical conductivity disintegration index Z
C
from (a) PEF
treatment time t
PEF
and (b) frequency f dependencies of tissue electrical conductivity σ.

34 Enhancing Extraction Processes in the Food Industry
electrical conductivity σ after PEF treatment with time constants from seconds to
hours is rather typical (Angersbach et al. 2002).
Electric impedance measurements and methods based on frequency dependency
of the phase shift in the range of 500 Hz–10 MHz were also applied for estimation
of electroporation effects in PEF-treated mash from wine grapes (Sack et al. 2009).
Good correlations were observed between measurements of the complex impedance
and color intensity of the must.
Finally, we noted that all conductivity-based methods for Z estimation are
straightforward and may be useful for the rough estimation of the impact of PEF
on plant tissues and colloidal biosuspensions (Lebovka et al. 2000; El Zakhem et al.
2006a,b; Vorobiev et al. 2006).
2.2.2.3 Diffusion Coefficient
Similarly, the diffusion coefcient disintegration index Z
D
can be dened as (Jemai
and Vorobiev 2001; Lebovka et al. 2007a)
Z
D
= (D – D
i
)/(D
d
– D
i
) (2.6)
where D is the measured apparent diffusion coefcient and subscripts i and d refer to
the values for intact and totally destroyed material, respectively.
The apparent diffusion coefcient D can be determined from solute extraction or
convective drying experiments. Unfortunately, diffusion techniques are indirect and
invasive for biological objects and can inuence the structure of tissues. Moreover,
there exists an equivalent problem with determination of D
d
. Drying experiments
with potato tissue have shown that the D
d
value of freeze–thawed tissue is noticeably
higher than the D
d
value of PEF-disintegrated tissue with a high Z
C
index (Lebovka et
al. 2007a). Evidently it reects cell wall damage after the freeze– thawing treatment.
2.2.2.4 Textural Characteristics
Some attempts in using textural methods for characterization of PEF-treated tis-
sues were done (Fincan and Dejmek 2003; Lebovka et al. 2004a). The pressure–
displacement and displacement–time (stress relaxation) curves were compared for
untreated and PEF-treated tissues (Grimi 2009; Grimi et al. 2009a). Differences in
the pressure–displacement curves (P–ε) for PEF-treated and untreated tissues were
usually observed (Lebovka et al. 2004a; Chalermchat and Dejmek 2005; Bazhal et
al. 2003b,c). Textural investigations (stress–deformation and relaxation tests) have
shown that tissues (carrot, potato, and apple) lose a part of their textural strength
after PEF treatment, and both the elasticity modulus and fracture stress decrease
with increase in the damage degree (Lebovka et al. 2004a). For PEF-treated apples,
linear dependency was observed between fracture pressure and the value of Z
C
(Bazhal et al. 2003b,c, 2004). These data were conrmed by investigations on the
textural and solid–liquid expression of PEF-treated potato tissues (Chalermchat
and Dejmek 2005). The effects of PEF on the compression and solid–liquid expres-
sion of different vegetable tissues were also extensively studied (Lebovka et al.
2004a; Jemai and Vorobiev 2006; Grimi et al. 2007; Praporscic et al. 2007a,b).

35Pulse Electric Field-Assisted Extraction
The compression-to-failure and stress–relaxation measurements of apple, carrot,
and potato tissues treated by PEF with different durations of treatment (t
PEF
) were
reported by Lebovka et al. (2004a). After a rather high-intensity, long-duration (E =
1.1 kV/cm, t
PEF
= 0.1 s) PEF treatment, the tissues partially lose their initial strength.
However, changes both in the elasticity modulus G
m
and the fracture stress P
F
were
signicantly smaller than changes observed for the freeze–thawed and thermally
(T= 45°C, 2 h) pretreated tissues. Thus, tissue structure seems to be less affected
by PEF treatment than by freeze–thawing or heating. This conclusion was later con-
rmed by textural studies on PEF-treated sugar beet tissue (Shynkaryk et al. 2008).
PEF treatment also accelerated the stress relaxation of tissues (Fincan and Dejmek
2003; Lebovka et al. 2004a, 2005a; De Vito et al. 2008). The relaxation behavior
reected the degree of membrane damage, but it was also sensitive to the state of the
cell walls and the turgor pressure. Note that freeze–thawed tissues usually demon-
strate faster relaxation than tissues treated by strong PEF (Lebovka et al. 2004, 2005a).
Note that the results of textural tests may depend on the mode of experiments—
for example, they may be different for experiments with uniaxial (1d) and three-
dimensional (3d) pressing. In 1d compression experiments, PEF treatment usually
leads to depression of P–ε curves—that is, ΔP = P
PEF
– P
i
< 0 (here P
PEF
and P
i
are
the pressures for PEF-treated and intact tissues, respectively) for the same level of
deformation ε (Lebovka et al. 2004a; Chalermchat and Dejmek 2005). The negative
value of ΔP for 1d pressing was explained by the softening of tissue texture after
PEF treatment followed by unconstrained liquid expression through the sidewalls
(Lebovka et al. 2004a; Chalermchat and Dejmek 2005). However, another behavior
was observed in experiments with 3d pressing (Grimi et al. 2009a), where the differ-
ence ΔP = P
PEF
– P
i
increases with the increase in deformation, ε. The positive value
of ΔP in this case was explained by constrained ltration through the lter cake and
higher stiffness of the network of cell walls saturated by intracellular liquid in PEF-
treated tissues. Moreover, the fracture pressure P
c
in 3d pressing experiments was
approximately the same for untreated and PEF-treated potato samples, P
c
≈ 4.5 ± 0.4
MPa. This value is noticeably larger than the fracture pressure (P
c
≈ 1.5–1.6 MPa)
of potato samples used in 1d pressing experiments (Chalermchat and Dejmek 2005).
It can be concluded that the textural parameters of plant tissues may indenitely
reect the PEF-induced changes in a complex form, although denitive relations
between these parameters and cell damage degree remain unknown. However, textural
experiments are rather useful for qualitative characterization of PEF-induced changes.
2.2.2.5 Acoustic Measurements
The acoustic technique is widely used for characterization of the quality of agri-
cultural products (García-Ramos et al. 2005). For example, its applications to apple
(Abbott et al. 1995), pineapple (Chen and De Baerdemaeker 1993), pear fruit (De
Belie et al. 2000), avocado (Galili et al. 1998), watermelon (Yamamoto et al. 1980),
and tomato (Schotte et al. 1999) tissues have been reported.
This technique allows measuring of the index of rmness F that shows good
correlations with the quality and maturity of fruits and vegetables (Chen and Sun
1991). The index F (or stiffness coefcient) is a dynamic characteristic dened as
f
2
m
2/3
ρ
1/3
, where f is the frequency corresponding to the maximum amplitude (A) in

36 Enhancing Extraction Processes in the Food Industry
the acoustic spectrum, m is the mass of the sample, and ρ is the density of the tested
tissue (Abbott et al. 1995; García-Ramos et al. 2005).
The successful application of the acoustic technique for characterization of PEF-
treated tissues was recently reported (Grimi et al. 2010). The acoustic disintegration
index Z
A
was dened as
Z
A
= (F – F
i
)/(F
d
– F
i
) (2.7)
where F is the measured index of rmness and subscripts i and d refer to the indices
of rmness of the intact (untreated) and completely damaged tissues, respectively.
Completely damaged tissue was obtained after freezing–thawing of the sample. Note
that the denition of Z
A
(Equation 2.7) is in clear analogy with the denitions of Z
C
(Equation 2.4) and Z
D
(Equation 2.6).
Note that the advantages of the acoustic technique for characterization of PEF-
induced effects may be important when fruits and vegetables are processed as whole
unpeeled samples. Examples of PEF application to whole samples have been demon-
strated for sugar beet (Sack et al. 2005) and potato (Jaeger et al. 2008). PEF can also
be attractive for treatment of other fruits and vegetables. The application of other
methods (e.g., microscopy, electrical conductivity, or diffusion coefcient measure-
ments) requires cutting and special preparation of samples; thus, they are destructive
and may be dependent on local tissue characteristics.
2.2.2.6 Correlations between Z Values Estimated by Different Techniques
Although the question of correlations between the values of damage degree estimated
by different techniques is rather important, it is not practically discussed in the litera-
ture. Figure 2.5 presents Z
C
versus Z
D
and Z
C
versus Z
A
dependencies obtained from
the data of PEF treatment experiments with potato and apple, respectively (Lebovka et
al. 2007a; Grimi et al. 2010). Note that the protocol of PEF treatment was the same for
the same product. The observed dependencies Z
C
(Z
D
) and Z
C
(Z
A
) were nonlinear and
were close to the power laws (i.e.,
Z Z
m
C D
D
=
and
Z Z
m
C A
A
=
), where m
D
= 1.68 ± 0.04
for potato and m
A
= 3.77 ± 0.26 for apple. The phenomenological theory (Archie 1942)
predicts nonlinear dependence between the conductivity disintegration index Z
C
and
real damage degree Z (i.e., Z
C
= Z
m
), and the estimated values of m fall within the range
of 1.8–2.5 for different plant tissues (apple, carrot, potato) (Lebovka et al. 2002). It was
assumed that the acoustic disintegration index Z
A
is better adapted for characterization
of damage degree characterization than the conductivity disintegration index Z
C
(Grimi
et al. 2010). Use of Z
C
results in a systematic underestimation of the damage degree. It is
rather important because at high values of real damage degree, Z ≈ Z
A
≈ 0.8–0.9, when
further PEF treatment is not efcient and gives no increase in Z value, the apparent con-
ductivity disintegration index seems to be small, Z
C
≈ 0.4–0.6 (Figure 2.4). However,
PEF overtreatment is not desirable and may result in excessive power consumption.
2.2.3 KinEtics of damagE
The kinetics of biological material damage under PEF processing is governed by the
mechanism of cell membrane electroporation.

37Pulse Electric Field-Assisted Extraction
The time dependence of the membrane damage may be approximated by the rst-
order kinetic equation (Weaver and Chizmadzhev 1996)
Z = exp(–t/τ) (2.8)
where τ is the damage time dependent on the transmembrane potential u
m
and char-
acteristics of membrane (τ
∞
,Q,u
o
)
τ
m
= τ
∞
exp(Q/(1 + (u
m
/u
o
)
2
)) (2.9)
The last equation follows from the uctuation theory of electroporation, and we can
refer as an example the typical values of τ
∞
≈ 3.7 × 10
–7
s, u
o
≈ 0.17 V, and Q ≈ 109,
experimentally estimated at 293 K for lipid membranes (Lebedeva 1987).
Cell membranes in food tissues or in suspensions are exposed to highly inho-
mogeneous electric elds. Thus, the experimentally estimated time dependence of
the damage degree Z may reect the complexity of electric eld distribution on the
membrane surface, which is related to distribution of cell sizes, cell shape anisot-
ropy, peculiarities of tissue structure, concentration of cells in suspension, and others
(Lebovka et al. 2002). The kinetics of material disintegration during PEF treat-
ment may be also inuenced by mass transport and resealing processes (Lebovka
0
1
0.8
0.6
0.4
0.2
0
0.2 0.4 0.6 0.8 1
0 0.2 0.4 0.6 0.8 1
Disintegration index (Z
D
)
Disintegration index (Z
A
)
Disintegration index (Z
C
)
Potato
400 V/cm
Apple
200 V/cm
FIGURE 2.5 Dependencies of Z
C
versus Z
D
and Z
C
versus Z
A
for potato and apple, respec-
tively. The pulse protocols were as follows: E = 400 V/cm, t
i
= 10
–4
s (potato) and E ≈ 300 V/
cm, t
i
= 10
–4
s (apple). The dashed lines correspond to the least square tting of the experi-
mental data to power equations
Z Z
m
C D
D
=
and
Z Z
m
C A
A
=
with m
D
= 1.68 ± 0.04 for potato and
m
A
= 3.77 ± 0.26 for apple. (Compiled from Lebovka, N.I. et al., J Food Eng, 78, 606–613,
2007a, and Grimi, N. et al., Biosyst Eng, 105, 266, 2010.)

38 Enhancing Extraction Processes in the Food Industry
etal. 2001; Knorr et al. 2001) and may be dependent on the PEF treatment protocol
(Lebovka et al. 2001).
Different empirical equations were used for approximation of experimental
dependencies in PEF damage kinetics (Barbosa-Canovas et al. 1998; Wouters and
Smelt 1997)—for example, Hulsheger’s equation (Hulsheger et al. 1983)
Z t
E E k
=
− −
( )
( )
/
c
/
τ (2.10)
Weibull’s equation (van Boekel and Martinus 2002)
Z = 1 – exp(–t/τ)
k
(2.11)
or the transition equation (Bazhal et al. 2003a)
Z = 1/(1 + (τ/t)
k
) (2.12)
Here τ, E
c
, and k are the empirical parameters.
Equations 2.10 through 2.12 fulll the conditions Z = 1 at t = 0 and Z = 1 at t = ∞.
2.2.3.1 Characteristic Damage Time
Equation 2.12 was successfully used for the approximation of damage evolution in
fruit and vegetable tissues (Bazhal et al. 2003a). It follows from Equation 2.12 that
Z = 0.5 at t = τ. Here τ is the characteristic damage time, which is dened as a time
necessary for half-damage of material (i.e., Z = 0.5) (see inset in Figure 2.6). This
measure is useful for crude characterization of damage kinetics, when the strict law
is unknown, yet it obviously differs from the rst-order kinetics law described by
Equation 2.8. Figure 2.6 presents examples of characteristic time τ versus electric
eld strength E for different vegetable and fruit samples (Grimi 2009). These data
were obtained for PEF-treated (by square wave pulses, duration t
i
= 100 μs) whole
products. Onions and oranges have stronger resistance to PEF treatment and require
longer treatment time or higher electric eld strength. In contrast, tomatoes and
apples have demonstrated weaker resistance to PEF than all the other tested prod-
ucts, and their τ values reach a minimum at E ≥ 400 V/cm. The effects observed for
PEF-treated whole products reect the specic structure of cellular materials, differ-
ences in the size of their cells, and differences in the relative electrical conductivities
of the product and the aqueous medium. Similar τ(E) dependencies for cut cubic
(1 cm
3
) apple, potato, cucumber, aubergine, pear, banana, and carrot samples were
reported by Bazhal et al. (2003a).
2.2.3.2 Synergy of Simultaneous Electrical and Thermal Treatments
An obvious synergy of simultaneous electrical and thermal treatments of food
products is usually observed (Vorobiev and Lebovka 2008; Lebovka et al. 2005a,b,
2007a). This synergy is most evident for electroprocessing at a moderate electric
eld strength (E < 100 V/cm) under ambient conditions, or only thermal processing
at a moderate temperature (T < 50°C). The thermal damage of a biomaterial under

39Pulse Electric Field-Assisted Extraction
ambient conditions is noticeable only if the duration of treatment exceeds 10
5
s and
could be accelerated only by increasing the temperature above 50°C.
Moreover, a rather complex kinetics with an intermediate saturation step (when
disintegration index Z reaches a plateau, Z = Z
s
) was often observed for long-duration
PEF treatment at a moderate electric eld (E < 300 V/cm) and a moderate tempera-
ture (T < 50°C) (Lebovka et al. 2001, 2007a). For example, the maximal disintegra-
tion index Z
s
was of the order of 0.75 at E = 100 V/cm for sugar beet tissue (Lebovka
et al. 2007a, 2008). The step-like behavior of Z(t) was also observed for inhomoge-
neous tissues such as red beetroots (Shynkaryk 2007; Shynkaryk et al. 2008). Such
saturation at the level of Z = Z
s
possibly reects the presence of a wide distribution
of cell survivability, related with different cell geometries and sizes. It was experi-
mentally observed that the saturation level Z
s
increases with increase of both electric
eld strength E (Lebovka et al. 2001) and temperature T (Lebovka et al. 2007b). For
tissues with relatively homogeneous structures (potatoes, apples, chicory, etc.), this
saturation behavior is less pronounced and not practically observed at higher electric
elds (E > 500 V/cm). If PEF treatment stops at the saturation level, the scenario of
the further evolution can be different depending on the type of material and the level
of its disintegration. The cells can partially reseal at a very small level of disintegra-
tion (Knorr et al. 2001). However, a higher level of disintegration usually results in
further increase of Z after a relatively long time (Lebovka et al. 2001; Angersbach
et al. 2002).
The synergy of simultaneous PEF and thermal treatment with increase in tem-
perature T or electric eld strength E (or both) was evidently demonstrated by the
10
2
10
1
10
0
10
–1
10
–2
10
–3
0 100 200 300 400 500 600
Electric field strength (E), V/cm
Characteristic damage time (τ), s
Distintegration index (Z)
PEF treatment time (t
PEF
)
Z=1
Z = 0.5
Z = 0
τ
Onion
Orange
Kiwi
Apple
Tomato
FIGURE 2.6 Characteristic time τ versus electric eld strength E for different vegetable
and fruit samples. Data were obtained from the measurements of acoustic disintegration
index of PEF-treated samples in tap water. (Compiled from data presented in Grimi, N., PhD
dissertation, University of the Technology of Compiègne, Compiègne, 2009.) The inset shows
schematic Z versus t dependence; here τ is the characteristic damage time, dened as the time
necessary for half-damage of material (i.e., Z = 0.5).

40 Enhancing Extraction Processes in the Food Industry
presence of a drastic drop of the characteristic damage time by many orders of mag-
nitude (Lebovka et al. 2005a,b, 2007b). Moreover, the electroporation activation
energy W of tissues was a decreasing function of electric eld strength E as a result
of electrothermal synergy (Loginova et al. 2010). This synergism of tissue damage
possibly reects the existence of softening transitions in membranes at tempera-
tures within 20–55°C (Exerova and Nikolova 1992; Mouritsen and Jørgensen 1997).
A noticeable drop of the breakdown transmembrane voltage u
m
of a single mem-
brane was experimentally observed near the region of thermal softening (≈50°C)
(Zimmermann 1986). The uidity and domain structure of the cell membrane exert
a noticeable inuence on electropermeabilization of cells (Kandušer et al. 2008).
The general relations between characteristic damage time τ, electric eld strength
E, and temperature T may be rather complex. These relations were studied in detail
for potato tissues. The following equation was used for the tting of experimental
data (Lebovka et al. 2005a)
τ
m
= τ
∞
exp(W/kT(1 + (E/E
o
)
2
) (2.13)
Here τ
∞
, W, and E
o
are adjustable empirical parameters. Note that that this equation
is fully empirical and resembles the form of Equation 2.1.
Interesting synergetic effects of simultaneous electrical and thermal treatments
were also observed in ohmic heating experiments (Lebovka et al. 2005a,b, 2007b). A
direct method based on experimental observations of electrical conductivity changes
during the ohmic heating was proposed for monitoring of electroporation changes,
and it was shown that ohmic heating at electric eld strength E of the order of 20–
80V/cm induced, inside the tissue, structural changes related to loss of membrane
barrier functions.
2.2.4 influEncE of pulsE control
Sale and Hamilton (1967) concluded that two main relevant parameters determine
the efciency of PEF damage: the electric eld strength (E) and the total time of
PEF (t
PEF
). Typically, higher electric eld strengths lead to better damage efciency
(Bazhal 2001; Bouzrara 2001; Praporscic 2005; Toep 2006; Shynkaryk 2007);
however, electrical power consumption and ohmic heating also become essential
at high electric elds. More detailed experiments have also shown that electro-
poration efciency may depend on the parameters of the pulse, such amplitude (or
electric eld strength E), shape, duration t
i
, number of repetitions n, and intervals
between pulses Δt (Canatella et al. 2001, 2004). A typical PEF protocol for bipolar
pulses of a near-rectangular shape is presented in Figure 2.7. Such complex pro-
tocol with adjustable long pause between pulse trains allows ne regulation of the
disintegration index Z without noticeable temperature elevation during the PEF
treatment.
2.2.4.1 Waveforms of PEF Pulses
The waveforms of pulses commonly used in PEF generators are exponential decay,
oscillatory, triangular, square, or more complex waveforms (Miklavcic and Towhidi

41Pulse Electric Field-Assisted Extraction
2010). The exponential decay, triangular, and square pulses may be either mono-
polar or bipolar. Square-wave generators are more expensive and require more
complex equipment than exponential decay generators. However, experiments with
inactivation of microbial cells have shown (Zhang et al. 1994) that application of
square-wave pulses resulted in better energy performance and higher disintegrating
efciency than exponential decay pulses. The superiority of square-wave pulses over
exponential decay pulses was explained by the better uniformity of electric eld
strength during each pulse application (Barbosa-Canovas and Altunakar 2006).
Bipolar pulses seem to be more advantageous as they cause additional stress in
membrane structure, allow avoiding asymmetry of membrane damage in the cell,
and result in more efcient electroporation responses (Saulis 1993, 2010; Fologea et
al. 2004; Talele et al. 2010). Moreover, application of bipolar pulses offers minimum
energy consumption, with reduced deposition of solids on electrodes and smaller
food electrolysis (Chang 1989; Qin et al. 1994; Wouters and Smelt 1997).
2.2.4.2 Pause between Pulses
The pause between pulses Δt may be an essential parameter affecting PEF electro-
poration efciency (Kinosita and Tsong 1979). It was shown that relaxation of the
conductivity of membranes was complete for a relatively long pause (Δt > 1 s); how-
ever, it was incomplete for high repetition frequency (above 1 kHz), and the initial
level of membrane conductivity for consecutive pulses increased. These results can be
explained by the existence of short- and long-lived transient (“transport”) membrane
pores (Pavlin et al. 2008). The inuence of distance between pulses Δt on disintegra-
tion of the apple tissue (Lebovka et al. 2001) and on inactivation of Escherichia coli
cells (Evrendilek and Zhang 2005) was also discussed. For example, it was shown
Pulse duration
Voltage
Distance between two pulses
∆t
∆t
t
t
i
t = N(n∆t/2+∆t
t
)
n∆t/2n∆t/2
n pulses
t
PEF
= Nnt
i
Series of N trains
Train Pause Train
Time
FIGURE 2.7 The typical PEF protocol. Bipolar square waveform pulses are presented. A
series of N pulses (train) is shown. Each separate train consists of n pulses with pulse duration
t
i
, pause between pulses Δt, and pause Δt
t
after each train. The total time of PEF treatment is
regulated by variation of the number of series N and is calculated as t
PEF
= nNt
i
.

42 Enhancing Extraction Processes in the Food Industry
that a protocol with a longer pause between pulses at xed values of E and t
PEF
allowed acceleration of the disintegration kinetics of apple tissue. The results were
explained, accounting for the moisture transport processes inside the cell structure.
However, the impact of pause between pulses on PEF-induced effects is still ambigu-
ous and requires a more detailed investigation in the future.
2.2.4.3 Pulse Duration
The impact of pulse duration t
i
on PEF-induced effects in treatment of plant tissues
and microbial species was also observed (Martin-Belloso et al. 1997; Wouters et al.
1999; Mañas et al. 2000; Raso et al. 2000; Aronsson et al. 2001; Abram et al. 2003;
Sampedro et al. 2007; De Vito et al. 2008). Some authors demonstrated that inactiva-
tion of microbes was more efcient at higher pulse width, subject to invariable quan-
tity of applied energy (Martin-Belloso et al. 1997; Abram et al. 2003), while others
observed little effect of pulse width on inactivation at equal energy inputs (Raso
et al. 2000; Mañas et al. 2000; Sampedro et al. 2007; Fox et al. 2008). The effect
of pulse width on microbial inactivation seems to vary depending on electric eld
strength; still, the obtained results are controversial (Wouters et al. 1999; Aronsson
et al. 2001). A critical review of the effect of pulse duration on electroporation ef-
ciency in relation to therapeutic applications was recently published (Teissié et al.
2008).
A distinct correlation between pulse duration and damage efciency was recently
observed in PEF treatment experiments with apples (De Vito et al. 2008). The theory
predicts deceleration of the membrane charging processes in materials with large
cell sizes (Kotnik et al. 1998). An efcient PEF treatment requires application of
relatively long pulses. To reach the maximum transmembrane voltage, the pulse
duration t
i
should be larger than membrane charging time t
c
. The experimental data
supported this conclusion and clearly demonstrated the inuence of pulse duration t
i
(10–1000 μs) on the efciency of PEF treatment of grapes, apples, and potatoes (De
Vito et al. 2008; Grimi 2010). Longer pulses were found to be more effective, and
their effect was particularly pronounced at room temperature and moderate electric
elds (E = 100–300 V/cm) (De Vito et al. 2008).
2.2.5 powEr consumption
The power consumption Q (mass density of the energy input) during PEF treatment
can be estimated from the following equation
Q t E dt
t
=
∫
σ ρ( )
2
0
/
(2.14)
Here ρ is the density of material.
It is usually assumed that electrical conductivity σ(t) is a complex function of
time, owing to the development of two processes during PEF treatment: damage
of material and temperature increase (related to ohmic heating). Both of these pro-
cesses result in increase in the value of σ(t).

43Pulse Electric Field-Assisted Extraction
The power consumption Q is the most important measure for estimation of indus-
trial attractiveness of any electrotechnology, and Q values have been reported for
PEF inactivation and extraction-oriented experiments.
The theoretical estimations predict that the product τE
2
, as well as the power
consumption Q, goes through a minimum with increase of the electric eld strength
E (Lebovka et al. 2002). Hence, there exists some optimum value of electric eld
strength E ≈ E
o
, which corresponds to minimum power consumption, and this pre-
diction was supported by experimental data obtained for different fruit and vegetable
tissues (Bazhal et al. 2003a). It was shown that an increase of E above E
o
resulted
in progressive increase of power consumption, but gave no additional increment to
the conductivity disintegration index Z. For some vegetable and fruit tissues (apple,
potato, cucumber, aubergine, pear, banana, and carrot), the typical values of E
o
were
within 200–700 V/cm and PEF treatment times required for effective damage, t
PEF
,
were within 1000 μs–0.1 s (Bazhal et al. 2003a). However, for grape skins, efcient
PEF-induced damage was observed at higher electric elds (1–10 kV/cm) for PEF
treatment times within 5–100 μs (López et al. 2008a). Note that the specic power
consumption may be roughly estimated from Equation 2.14 as
Q ~ σ
d
E
2
t
PEF
/ ρ (2.15)
where σ
d
is the electrical conductivity of the totally damaged tissue (Lebovka et al.
2002).
Putting σ
d
= 0.1 S/cm and ρ = 0.8 × 10
3
kg/m
3
(these are the typical values for
apples (Lebovka et al. 2000), we obtain approximately the same value, Q ≈ 3 kJ/kg,
both for treatment by moderate electric eld (E = 500 V/cm and t
PEF
= 10000 μs) and
by high electric eld (E = 5000 V/cm and t
PEF
= 100 μs).
However, in the general case, estimations of the values of E
o
and Q require more
thorough accounting of the tissue structure, tissue heterogeneity, cell geometry, and
other factors (Ben Ammar et al. 2011). An approximate proportionality in behavior
of characteristic damage time τ and power consumption Q was observed for differ-
ent fruit and vegetable tissues (Figure 2.8). Comparisons of theory and experiment
have shown that the optimal values of E
o
and power consumption Q may be critically
dependent on electrical conductivity contrast—that is, the difference between elec-
trical conductivities of intact (σ
i
) and completely damaged (σ
d
) tissues (Figure 2.8).
Figure 2.9a displays power consumption Q (Z
C
= 0.8) versus electric eld strength
E for two values of electrical conductivity contrast k = σ
i
/σ
d
as predicted by Monte
Carlo simulations (Ben Ammar et al. 2011). Theory predicts the increase of E
opt
and Q(E
opt
) values with the decrease in electrical conductivity contrast, k = σ
i
/σ
d
.
The same tendency was experimentally observed in PEF-treated potato and orange
(Figure 2.9b). With increase of E from 400 V/cm to 1000 V/cm, the power consump-
tion Q, required for attaining of the given level of disintegration, Z
D
= 0.8, increased
for potato (high k, k ≈ 14) and decreased for orange (small k, k ≈ 1.3).
The experimentally estimated power consumptions Q for PEF-treated tissues
were found to be rather low and typically lying within 1–15 kJ/kg. For example, they
were 6.4–16.2 kJ/kg (E = 0.35–3.0 kV/cm) for potato (Angersbach et al. 1997), 0.4–
6.7 kJ/kg (E = 2–10 kV/cm) for grape skin (López et al. 2008a), 2.5 kJ/kg (7 kV/ cm)

44 Enhancing Extraction Processes in the Food Industry
10
–1
10
–2
10
–3
20
15
10
5
0
Characteristic
damage time (τ), s
Power consumption
(Q), kJ/kg
Orange
(a)
(b)
Banana Courgette Carrot Apple Potato
Orange Banana Courgette Carrot Apple Potato
FIGURE 2.8 Power consumption Q (Z
C
= 0.8) versus electric eld strength E at different
values of k = σ
i
/σ
d
: (a) results of Monte Carlo simulations and (b) experimentally estimated
values for potato and orange. (Compiled from the data presented by Ben Ammar, J. et al.,
JFood Sci, 76, E90–E97, 2011.)
15
(a)
(b)
10
15
10
2
10
3
5
0
10
5
0
Potato
400
1000
σ
d
/σ
i
≈ 14
σ
d
/σ
i
≈ 1.3
σ
d
/σ
i
= 2
σ
d
/σ
i
= 10
Electric field strength (E), V/cm
E, V/cm
Power consumption (Q), kJ/kg
–1
Orange
FIGURE 2.9 Correlations between characteristic damage time τ and power consumption Q
for different fruit and vegetable tissues. The value of Q was estimated at a relatively high level
of disintegration (Z
C
= 0.8) for PEF treatment at E = 400 V/cm with 1000 μs bipolar pulses of
near-rectangular shape. (Compiled from the data presented by Ben Ammar, J. et al., J Food
Sci, 76, E90–E97, 2011.)

45Pulse Electric Field-Assisted Extraction
for red beetroot (López et al. 2009a), 3.9 kJ/kg (7 kV/cm) for sugar beet (López et al.
2009b), and 10 kJ/kg (400–600 V/cm) for chicory root (Loginova et al. 2010).
Thus, from the standpoint of power consumption, the PEF method is practically
ideal for the production of damaged plant tissues as compared to other methods of
treatment such as mechanical (20–40 kJ/kg), enzymatic (60–100 kJ/kg), and heating
or freezing–thawing (>100 kJ/kg) (Toep et al. 2006). However, bacterial inactiva-
tion and food preservation requires high electric eld strengths (E
o
= 15–40 kV/cm),
and it naturally results in a noticeably higher specic power consumption, of the
order of 40–1000 kJ/kg (Toep et al. 2006). Such power consumption is also typical
for HVED (Boussetta et al. 2009). Hydroxide treatment at a moderate electric eld
(typically 20–80 V/cm) requires high power consumption, typically comparable with
heating or freezing–thawing (20–40 kJ/kg).
2.3 PEF-ASSISTED EXTRACTION
2.3.1 VEgEtaBlE and fruit tissuEs
In raw food plants, valuable compounds are initially enclosed in cells, which have
to be damaged for facilitation of intracellular matter recovery. Conventional cell
damage techniques, such as ne mechanical fragmentation and thermal, chemical,
and enzymatic treatments, lead to more severe disintegration of the tissue compo-
nents, including cell walls and cell membranes. PEF treatment, which is less destruc-
tive than conventional methods, can be used for a more selective extraction of cell
components.
2.3.1.1 Potato
Potato was used as a model system in many electrically assisted experiments for test-
ing electroporation effects in plant tissues (Angersbach et al. 1997, 2000; Lebovka et
al. 2005a,b, 2006, 2007a; Galindo et al. 2008a,b; Pereira et al. 2009). The presence
of reversible electroporation has been reported for potato tissue (Angersbach et al.
2000; Galindo 2008; Pereira et al. 2009). This process involved formation of pores
after 0.7 μs of membrane charging; however, the vitality and metabolic activity of
potato cells were recovered within seconds after electric eld shutdown (Angersbach
et al. 2000). The transient processes in the viscoelastic behavior of potato during
PEF application at E = 30–500 V/cm followed by recovery of cell membrane prop-
erties and turgor were attributed to consequences of electroporation (Pereira et al.
2009). The reversibility of electropermeabilization was dependent on PEF param-
eters and different stress-induced effects, and metabolic responses were observed
(Lebovka et al. 2008; Galindo et al. 2008a,b; Pereira et al. 2009; Galindo 2009). It
was shown that the effects of low-temperature permeabilization of potato at 50°C
were stimulated by preliminary electric eld treatment (Lebovka et al. 2008). Mild
PEF treatment allows the recovery of the functional properties of membranes, and
metabolic responses may arise in a time scale of seconds (Galindo et al. 2008a,b).
Isothermal calorimetry, electrical resistance, and impedance measurements have
shown that 24h after PEF treatment, the metabolic response of potato tissue involved
oxygen-consuming pathways (Galindo et al. 2009a,b). The metabolic responses were

46 Enhancing Extraction Processes in the Food Industry
strongly dependent on the PEF protocol and were independent of total permeabiliza-
tion. It was shown that even mild electrical treatment of potato permeabilizes tissue,
and this effect could be seen in electrical conductivity behavior 24 h after the treat-
ment (Kulshrestha and Sastry 2010).
The effects of PEF treatment on the textural and compressive properties of potato
were studied in detail (Fincan and Dejmek 2003; Lebovka et al. 2004a; Chalermchat
and Dejmek 2005; Grimi et al. 2009a). It was shown that relatively strong PEF
treatment resulted in decrease in the stiffness of potato tissues to levels similar to
hyperosmotically treated samples (Fincan and Dejmek 2003). 1D force textural
investigations (stress–deformation and relaxation tests with unconned potato sam-
ples) have shown that the tissue loses a part of its textural strength after PEF treat-
ment, and both the elasticity modulus and fracture stress decrease with increase in
damage degree (Lebovka et al. 2004a). These data were conrmed by textural and
solid–liquid expression investigations of PEF-treated potato tissues (Chalermchat
and Dejmek 2005). It was also shown that the application of PEF treatment only was
not sufciently effective for complete elimination of textural strength; however, mild
thermal pretreatment at 45–55°C allowed to increase PEF efciency (Lebovka et al.
2004). 3d textural investigations (of conned potato samples) with the applied pres-
sure varying within 0.5–4 MPa showed that fracture pressure was approximately
the same for both PEF-treated and untreated specimens, but PEF-treated tissues dis-
played higher stiffness than untreated ones (Grimi et al. 2009a). The critical pressure
P
m
, at which the time the pressure-induced cell rupture should be of the same order
of magnitude as the time of uid expression from the damaged cells, was estimated
as P
m
≈ 6 MPa.
Potato tissue was used for detailed studies of the effects of temperature and the
PEF protocol on the characteristic damage time (Lebovka et al. 2002, 2005a), dehy-
dration (Arevalo et al. 2004), freezing (Jalté et al. 2009; Ben Ammar et al. 2009,
2010), and drying (Lebovka et al. 2007a). However, despite the numerous funda-
mental studies of PEF effects in potato, attempts in extraction-oriented applica-
tion of PEF treatment are still rare. One can refer to the work by Propuls GmbH
(Bottrop, Germany) on PEF application for facilitation of starch extraction from
potato (Loefer 2002; Top 2006). It was shown that PEF treatment also allowed
the enhancement of the extractability of an anthocyanin-rich pigment from purple-
eshed potato (Top 2006). Note that the effects of PEF on the structure of potato
starch were recently revealed (Han et al. 2009). Starch granules lost their shape after
PEF treatment at 30–50 kV/cm: dissociation, denaturation, and damage of potato
starch granules were observed. However, sequential PEF (at 400 V/cm) and osmotic
pretreatments of potato tissue resulted in starch granules with a rougher surface. A
noticeable disordering of the surface morphology of starch granules inside potato
cells in the freeze-dried potatoes after sequential PEF and osmotic pretreatment was
also observed (Ben Ammar et al. 2009, 2010).
2.3.1.2 Sugar Beet
The extraction technology conventionally used in the sugar industry is a power-
consuming hot water technique. It involves diffusion of sugar from sliced sugar beet
cossettes at 70–75°C. A relatively high temperature is required for tissue denaturation

47Pulse Electric Field-Assisted Extraction
by heat. Unfortunately, treatment by heat also causes alterations in cell wall structure
through hydrolytic degradation reactions (molecular chain breakage, detachment of
polysaccharide fragments) (Van der Poel et al. 1998). The elastic properties of tissues
can be strongly affected by thermal treatment. Moreover, cell components other than
sugar, such as pectin, pass into the juice during extraction, thus affecting juice purity.
In addition, formation of some colorants such as melanoidins is promoted by thermal
diffusion. This results in the necessity for the application of a complex multistage
process (preliming, liming, rst and second carbonation, several ltrations, and sul-
tation) and lime discharge (3–3.2 kg of limestone for 100 kg of beetroot) for juice
purication (Van der Poel et al. 1998).
The diffusion process in the sugar extraction technology can be intensied by
electric eld treatment. Early investigations show that application of low-gradient
alternating electric elds (<100 V/cm) can enhance the juice extraction process
(Zagorulko 1958) and increase the soluble matter diffusion coefcient in the sugar-
beet (Bazhal et al. 1983; Katrokha and Kupchik 1984; Jemai 1997). Therefore, PEF
is a potential alternative method to conventional thermal technology.
Previous experimental studies have shown in principle the possibility of sugar
extraction by cold or moderately heated water (Jemai and Vorobiev 2003). The
strong dependence of damage efciency on temperature and pulse protocol parame-
ters was recently demonstrated in sugar beets (Lebovka et al. 2007b). The Arrhenius
form of the characteristic damage time versus inverse temperature dependencies was
observed both for electrical and thermal processes with activation energies within
W = 149–166 kJ/mol. Such large activation energies correspond to the membrane
damage of sugar beet cells. The thermal and cold diffusion kinetics and diffusion
coefcients D
eff
for untreated and PEF-treated (E = 400 V/cm, t
PEF
= 0.1 s) sugar
beet slices (1.5 mm × 10 mm × 10 mm) were compared (Lebovka et al. 2007b).
PEF treatment noticeably accelerated the aqueous diffusion of sugar from the sliced
cossettes. The Arrhenius dependencies of the effective diffusion coefcient D
eff
ver-
sus inverse temperature were observed with activation energies of 21 ± 2 kJ/mol
and 75 ± 5 kJ/ mol for the PEF-treated and untreated sugar beet slices, respectively
(Figure2.10). The activation energy of PEF-treated slices was close to that character-
istic for sugar diffusion in aqueous solutions, W ≈ 22 kJ/mol (Lysjanskii 1973). The
larger activation energy for the untreated slices possibly reects interrelations of the
effects of restricted diffusion and thermally induced damage (Lebovka et al. 2007b).
At 70°C, the effective diffusion coefcient D
eff
was nearly the same for untreated
and PEF-pretreated slices (1 × 10
–9
–1.5 × 10
–9
m
2
/s). The difference in D
eff
values
of the untreated and PEF-pretreated tissues increased signicantly for less heated
tissue. For instance, the values of D
eff
were nearly the same for sugar diffusion from
untreated tissue at 60°C and from PEF-pretreated tissue at 30°C. The purest juice
was obtained after cold diffusion. However, even after thermal diffusion at 70°C,
juice purity was higher for slices pretreated by PEF than for untreated slices.
Diffusion experiments with PEF-treated cossettes prepared from sugar beet using
industrial knives were recently done under electric eld strength E varying between
100 and 600 V/cm and total time of PEF treatment t
PEF
= 50 ms (Loginova et al.
2011). Figure 2.11 presents the temperature dependencies of diffusion juice purity
P and sucrose concentration S in experiments with untreated and PEF-treated sugar

48 Enhancing Extraction Processes in the Food Industry
14
12
10
8
6
4
30 40 50 60 70
30
92
88
84
80
76
40 50 60 70
Temperature, ˚C
Temperature, ˚C
Sucrose, ˚S
PEF-treated
PEF-treated
Intact
Intact
Purity, %
FIGURE 2.11 Temperature dependencies of diffusion juice purity P and sucrose concentra-
tion S in experiment with untreated and PEF-treated sugar beet cossettes. PEF treatment was
done at E = 600 V/cm; the pulse duration t
i
was 100 μs; and the total time of PEF treatment
t
PEF
was 50 ms, which corresponded to 5.4 kW·h/t of power consumption. (From Loginova,
K.V. et al., J Food Eng, 102, 340–347, 2011. With permission.)
70 60 50 40 30
0.0029 0.003 0.0031 0.0032
1/T, K
–1
10
–9
10
–10
T, °C
D
eff
, m
2
/s
0.0033
PEF pretreated
Untreated
FIGURE 2.10 Arrhenius plots of the effective diffusion coefcient D
eff
for the untreated
and PEF-pretreated sugar beet slices. (From Lebovka, N. et al., J Food Eng, 80, 639–644,
2007b. With permission.)

49Pulse Electric Field-Assisted Extraction
beet cossettes. For the untreated cossettes, the sucrose content in the cold diffusion
juice was very low (<6% at 30°C) and the purity of cold juice was <80%. For the
PEF-treated cossettes, the soluble solids and the sucrose content in the cold diffusion
juice (30°C) were slightly lower than in the hot diffusion juice (70°C). However, the
purity of the cold diffusion juice (30°C) was not lower than that of the hot (70°C)
juice (Figure 2.11a). Some studies even showed that the purity of the cold diffusion
juice is higher than that of the hot juice (Lebovka et al. 2007b). It was also shown
(Loginova et al. 2011) that sugar beet pulp could be well exhausted by cold or mild
thermal extraction of PEF-treated cossettes, and the pulp obtained by cold extrac-
tion of PEF-treated cossettes had a noticeably higher (>30%) dryness than that of the
pulp obtained by conventional hot water extraction. The estimated energy surplus for
cold extraction with a temperature reduction from 70°C to 30°C (i.e., by ΔT = 40°C)
was ≈46.7 kW·h/t, and was noticeably higher than the power consumption required
for PEF treatment, ≈5.4 kW·h/t. Loginova et al. (2011) concluded that such power
consumption can even be reduced by further optimization of PEF parameters and
minimization of the liquid-to-solid ratio during PEF treatment.
The different aspects of PEF-assisted pressing and aqueous extraction from sugar
beets were recently studied (Bouzrara and Vorobiev 2000, 2001, 2003; Eshtiaghi and
Knorr 2002; El-Belghiti and Vorobiev 2004, 2005a,b; El-Belghiti 2005; Vorobiev et
al. 2005; Praporscic et al. 2005; Jemai and Vorobiev 2006). The efciency of the so-
called cold pressing of PEF-treated sugar beet cossettes was demonstrated (Bouzrara
and Vorobiev 2000, 2003; Eshtiaghi and Knorr 2002). Jemai and Vorobiev (2006)
reported that up to 82% of the overall yield could be achieved by a two-stage press-
ing with an intermediate PEF application (E = 400 V/cm, t
PEF
= 0.1 s). Initial pres-
surization served to assure good electrical contact between slices. In addition, juices
obtained after PEF application (the so-called second juices) systematically had
higher sugar content and better color. PEF treatment was successfully applied in
scale-up experiments aimed at developing a novel process of cold juice extraction
from sugar beet cossettes (Jemai and Vorobiev 2006). The processing scheme con-
sisted of two initial pressing steps with an intermediate PEF treatment, followed by
one or more washing steps and a nal pulp pressing (pressure of 5–15 bar; particles
lling of 4.5–15 kg). The cold juices expressed from sugar beet gratings after an
intermediate PEF treatment had higher purity (95–98%) than those obtained before
PEF application (90–93%). The losses of sugar in the pulp could be signicantly
reduced to about 3% of the initial sugar content through some washing and nal
pressing operations. The quantity of pectin was noticeably lower, and the color of
juice was 3–4 times less intensive than the color of factory juices. In addition, sig-
nicant amounts of potassium, sodium, and α-amino nitrogen were found to remain
in PEF-treated particles, which explains why better-purity juices were obtained after
PEF treatment (Jemai and Vorobiev 2006). These results demonstrating signicant
amelioration of juice quality open new interesting prospects of cold PEF-enhanced
expression from the sugar beets.
El-Belghiti et al. (2005a,b) studied the inuence of PEF intensity and duration on
the static and centrifugal aqueous extraction from coarse sugar beet slices (1.5 mm
in thickness) obtained on a 6 mm grater. The solute yield was signicantly increased
with PEF treatment at E = 670 V/cm: it was about 40% for untreated slices, and

50 Enhancing Extraction Processes in the Food Industry
a yield of 93% was attained after PEF treatment and 2 h of extraction at ambient
temperature. Further increasing the PEF intensity up to 800 V/cm was not effective.
Centrifugal diffusion of slices was done with a liquid-to-solid mass ratio (L/S) of 3,
and under different centrifugal accelerations (150–9660 × g) and temperatures (18–
35°C). The extraction kinetics was much faster in the centrifugal eld. For instance,
the solute yield after PEF treatment reached 97% after 60 min of extraction even at a
low centrifugal acceleration (14 × g) and at a temperature of 25°C. At high centrifu-
gal acceleration (150 × g), a solute concentration of 97% was reached after 25 min
of aqueous extraction at 25°C and just after 15 min of aqueous extraction at 35°C.
2.3.1.3 Sugar Cane
The effect of PEF pretreatment at 4–5 kV/2.5 cm on the disintegration of sugar cane
was recently investigated (Kuldiloke et al. 2008). Sugar canes were cut into 10- to
15-cm-length cylinders, placed in a treatment chamber containing tap water, treated
with PEF, cut into small pieces of approximately 3 × 3 mm length and 1 mm thick-
ness, and then pressed. It was shown that PEF pretreatment at room temperature
is a suitable method for permeabilization of sugar cane. The juice yield of PEF-
pretreated samples was higher (74.5%) than that of the heat-treated (73.2%, 20 min
at 70°C) and untreated (65.5%) sugar cane, and the power consumption of PEF (17
kJ/ kg) was 10 times less than that of heat treatment (171 kJ/ kg).
2.3.1.4 Red Beet
Red beets (Beta vulgaris L.) are widely used for the industrial production of natu-
ral water-soluble betalain pigments based on red-violet betacyanins (betanine) and
yellow-orange betaxanthins (Stinzing and Carle 2004, 2007, 2008). Betalains exhibit
good antiviral and antimicrobial activities and may be considered useful cancer-
preventive agents, while betaxanthins may be used as a source of essential dietary
amino acids (Delgado-Vargas and Paredes-López 2003). Betalains have potent anti-
oxidant activity, conferring protection against degenerative diseases (Azeredo 2009).
These pigments are usually produced by long-term solid–liquid extraction at room
temperature (Delgado-Vargas et al. 2000; Delgado-Vargas and Paredes-López 2003)
or by pressing grinded red beetroots followed by pasteurization of the resulting juice
(Stinzing and Carle 2004, 2007, 2008). However, the stability of betalains is rather
sensitive to temperature, presence of metals, pH, water activity, light exposure,
enzymes, and oxygen (Saguy et al. 1978; Herbach et al. 2004; Stinzing and Carle
2004, 2007, 2008).
All of these factors complicate the extraction process, hinder extraction kinetics,
and reduce the yield of colorants from the red beet. PEF treatment allows overcoming
the restrictions typical for thermally sensitive bioproducts. A high degree of extract-
ability of colorants from the red beetroot was observed after PEF treatment at the
eld strength 1 kV/cm, when samples released about 90% of their total red pigment
following 1 h of aqueous extraction (Fincan et al. 2004; Chalermchat et al. 2004).
The mechanism of electroporation was found to be responsible for acceleration of dye
extraction from the red beet by moderate electric eld treatment (Kulshrestha and
Sastry 2003). A possibility of DC-assisted extraction and separation of the red beet
pigment was also demonstrated (Zvitov et al. 2003; Zvitov and Nussinovitch 2005).

51Pulse Electric Field-Assisted Extraction
Lopez et al. (2009a) showed that application of the PEF treatment at 7 kV/cm
enabled increasing the maximum yield of betanine by a factor of 4.2 compared to
samples not subjected to PEF treatment, and achieved an almost complete betanine
release. A combination of PEF at 7 kV/cm and pressing at 14 kg/cm
2
shortened the
time of extraction by 18-fold. It can be noted that effective electroporation of the red
beet tissue at ambient temperatures can be attained even at lower electric elds of
400–600 V/cm, and it allows acceleration of drying of the red beet tissue (Shynkaryk
et al. 2008).
2.3.1.5 Carrot
Carrots are vegetables containing both water-soluble (mainly soluble sugars) and
water-insoluble (carotenoids) components. They are rich in sugars, as indicated
by their sweetness. In addition, the main components of the cellular juice (°Brix
j
)
include soluble sugars such as sucrose (56.9%), glucose (24.6%), and fructose (18.5%)
(Rodríguez-Sevilla et al. 1999). There exist many examples of PEF application for
the expression (Knorr et al. 1994; Bouzrara 2001; Praporscic et al. 2007b) and
extraction (El-Belghiti and Vorobiev 2005a,b; El-Belghiti et al. 2007; Grimi et al.
2007) of juice from carrots.
The carrot juice yield increased from 30–50% to 70–80% as a result of PEF pre-
treatment (Knorr et al. 1994; Rastogi et al. 1999). PEF treatment (at E = 220–1600 V/
cm) accelerated the osmotic dehydration of carrots, and the effective diffusion coef-
cients of water and solute increased exponentially with electric eld strength. It was
demonstrated that a large juice yield could be attained even at a rather low voltage
gradient of 360 V/cm, and juice expressed after PEF treatment are more transparent
and less turbid than that from untreated carrots (Bouzrara 2001). Moreover, the °Brix
values instantly increased after PEF treatment (Praporscic et al. 2007b). The effects of
PEF treatment (at 25 and 30 kV/cm) on the release of carotenoids in an orange–carrot
juice mixture (80:20, v/v) was studied by Torregrosa et al. (2005). Liquid chromatog-
raphy was used for quantication of carotenoids, and PEF processing was shown to
result in a signicant increase in carotenoid and vitamin A concentrations.
The kinetics of extraction from carrot slices obtained by grating carrots in a
6 mm grater (1.5-mm-thick coarse slices) or in a 2 mm grater (0.5 mm thick ne
slices) were studied by El-Belghiti and Vorobiev (2005a,b). They showed that ne
and coarse slices demonstrated almost the same extraction kinetics after PEF treat-
ment at E = 550 V/cm. This conrms the attractiveness of PEF treatment especially
for coarse particles. In the absence of PEF pretreatment, only 45% of solute was
obtained from the coarse slices after 8 h of extraction at 18°C. The increase in stir-
ring speed up to 250 per minute enhanced extraction kinetics. An energy input of
9 kJ/kg was considered as optimal and was maintained to optimize the diffusion
parameters (duration, temperature, and stirring velocity).
The centrifugal aqueous extraction of solute (accelerations from 14 ×
g to 5434 ×
g) from the carrot gratings treated by PEF at 670 V/cm (300 pulses of 100 μs) was
investigated at temperatures within 18–35°C (El-Belghiti et al. 2005, 2007). It was
shown that an increase of the centrifugal acceleration up to 150 ×
g enhanced extrac-
tion kinetics, and tissue preheating at 50°C allowed easier electrical permeabiliza-
tion of the cell membranes.

52 Enhancing Extraction Processes in the Food Industry
Grimi et al. (2007) studied carrot juice extraction using laboratory lter-press
chamber with different combinations of pressing and washing operations. For the
smallest slices (0.078 × 0.078 × 2 mm), the washing–pressing procedure gave the
highest Brix of the juice and PEF provided no additional effect on the juice yield and
soluble matter content. However, the resulting juice was highly clouded; it contained
cell wall residues and was rich in submicrometer suspended particles. For the largest
slices (7 × 2 × 30 mm), PEF application noticeably improved the yield and soluble
matter content of the juice, but left most of the carotenoids inside the press cake. An
example of PEF application to extract juice from large slices of carrots evidenced the
possibility of selective extraction of water-soluble components (soluble sugars) and
the production of a “sugar-free” concentrate rich in vitamins and carotenoids, which
can be used as an additive in dietary foods (Grimi et al. 2007).
PEF also inuence carrot drying and rehydration (Gachovska et al. 2008;
Gachovska et al. 2009a). Carrots pretreated at E = 1000–1500 V/cm showed a higher
drying rate; however, the rehydration rate of PEF-pretreated carrots was lower than
that of blanched carrots. It was also shown that PEF pretreatment reduced peroxidase
activity by 30–50%, while blanching completely inactivated the enzyme (>95%).
2.3.1.6 Apple
The effects of electropermeabilization on apple tissues have been studied by differ-
ent investigators (Angersbach et al. 2000; Bazhal and Vorobiev 2000; Lebovka et
al. 2001, 2002; Bazhal et al. 2003c,d; De Vito et al. 2008; Chalermchat et al. 2010;
Grimi et al. 2010). Models of dielectric breakage were developed and tested using
experimental data obtained from PEF-treated apple tissues (Lebovka et al. 2001,
2002). These models accounted for the resealing of cells and the moisture transfer
processes that occur inside the tissues. A mathematical model was also developed to
describe the elastic properties of PEF-treated apples (Bazhal et al. 2004). The effects
of apple tissue anisotropy and orientation with respect to the applied electric eld on
electropermeabilization were reported (Grimi et al. 2010; Chalermchat et al. 2010).
It was shown that elongated cells (taken from the inner region of the apple paren-
chyma) responded to the electric eld in a different manner, while no eld orientation
dependence was observed for round cells (taken from the outer region of the paren-
chyma) (Chalermchat et al. 2010). The effects of PEF treatment on the textural and
biomechanical properties of apple tissues were also intensively discussed (Bazhal et
al. 2003d; Wu and Guo 2009). A linear dependency was observed between failure
stress and conductivity disintegration index (Bazhal et al. 2003d). It was shown that
PEF treatment (at 1000 V/cm) decreased bulk density, decreased volume shrinkage,
and increased porosity of air-dried apple tissues (Bazhal et al. 2003b,c,d). The size
of the PEF-induced pores was comparable with the cell wall thickness. The textural
relaxation data suggest a higher damage efciency of longer pulse durations on apple
tissues (De Vito et al. 2008). Textural tests have shown that shear strength, compres-
sion yield strength, rmness, and elastic moduli of the PEF-treated apple samples
are lower than those of the untreated control group. The synergy of PEF and the
effect of thermal treatment on the textural properties of apple tissues and apple juice
expression were demonstrated (Lebovka et al. 2004a). It was shown that mild ther-
mal treatment allows to increase the damage efciency of PEF treatment, and apple

53Pulse Electric Field-Assisted Extraction
tissue preheated at 50°C and treated by PEF at E ≈ 500 V/cm exhibited a noticeable
enhancement of juice extraction by pressing (Lebovka et al. 2004a,b).
Jemai and Vorobiev (2001, 2002) studied the apparent diffusion coefcient D in
both thermally and electrically (E = 100–500 V/cm, t
PEF
= 0.1s) treated apple discs
(Golden Delicious) and demonstrated that detectable enhancement of the diffusion
kinetics started at eld intensities within 100–150 V/cm. Further increase both in
theeld intensity and pulse duration led to further enhancement of diffusion kinet-
ics. It was shown that for the thermally treated samples, the temperature variation
of the diffusion coefcient D was of Arrhenius type with two diffusion regimens:
(i) without thermal pretreatment (E
a
~28 kJ/mol) and (ii) after thermal denatur-
ation(E
a
~13 kJ/mol). Only one regimen with intermediate activation energy (E
a
~20
kJ/mol) was observed for electrically treated samples. Furthermore, it was found that
electrical pretreatment with moderate temperature elevation (10–15°C) combined
with a low temperature treatment signicantly enhanced the diffusion coefcient
D compared with the reference values (Jemai and Vorobiev 2002). It indicates that
electrical treatment has a greater effect on the structure and permeability of apple
tissue than thermal treatment.
The effects of PEF on drying and osmotic dehydration of apples have been widely
discussed in the literature (Taiwo et al. 2003; Arevalo et al. 2004; Amami et al. 2005,
2006; Liu and Guo 2009). PEF treatment can decrease the drying rate, improve the
quality of dried product, and reduce the power consumption (Liu and Guo 2009).
PEF was used for acceleration of osmotic dehydration; it was reported that PEF
treatment at 0.5–2.0 kV/cm improved mass transfer during osmotic dehydration. The
vitamin C content of dried apples was reduced at higher eld strengths and lon-
ger immersion times (Taiwo et al. 2003). PEF application at 900 V/cm increased
both convection and diffusion rates and resulted in decreased sugar concentration
in the osmotic solution and higher solid content in apples (Amami et al. 2005). The
increase in solute (sucrose) concentration and PEF treatment resulted in the accelera-
tion of osmotic dehydration. The PEF-treated apples exhibited higher water loss and
higher solid gain than the untreated apples; the effect of PEF was more pronounced
for water loss than for solid gain (Amami et al. 2006).
Different research groups have studied the inuence of PEF treatment on juice
expression from apples (Bazhal and Vorobiev 2000; Bazhal et al. 2001; Jemai and
Vorobiev 2002; Lebovka et al. 2003, 2004b; Praporscic et al. 2007b; Schilling et al.
2007; Vorobiev et al. 2007; Turk et al. 2010a). It was observed that in ne-cut apples,
a combination of pressing and PEF treatment gives optimum results, signicantly
enhances the yield of juice, and improves juice quality (Bazhal and Vorobiev 2000).
Enhancement of the juice yield Y after PEF application was accompanied with a
noticeable decrease in absorbance and increase in Brix value of the juice (Praporscic
et al. 2007b). The reported improvement of the juice yield was more or less signi-
cant, probably due to the different process conditions employed in different studies
(degree of particle fragmentation, PEF parameters, and compression pressure).
PEF application allowed increase of juice yield from apple slices (Praporscic et al.
2007a) and apple mash (Schilling et al. 2007). The time of PEF application and the
size of slices noticeably affected juice characteristics (Praporscic et al. 2007b). The
size of particles and the method of fragmentation (slicing, grinding, or milling) can

54 Enhancing Extraction Processes in the Food Industry
be essential for the improvement of juice yield. Recently, it was demonstrated (Grimi
2009; Grimi et al. 2011) that the yield of juice, obtained from 2 × 3.5 × 55mm slices
of Golden Delicious apples, increased after PEF treatment (E = 400 V/cm, t
PEF
= 0.1s)
by 28%, but only by 5% when the apples were more nely sliced (1 × 1.9 × 55 mm).
Finely slicing the apples caused most of the cells to be disrupted mechanically, and
the additional effect of PEF on the total juice yield from such material is rather lim-
ited. On the contrary, when particles are coarse, the percentage of electrically dam-
aged cell membranes increases, but the cell wall structure is less affected. It might
be the cause of the more transparent and less cloudy apple juices obtained after PEF
treatment of coarse particles (Bazhal and Vorobiev 2000; Praporscic et al. 2007b).
No apparent change in pH value and total acidity of juice was detected. Moreover,
the content of many nutritionally valuable compounds was retained or even enhanced
(Jaeger et al. 2008). Schilling et al. (2008a,b) reported a comparative study of apple
juice production using PEF treatment and enzymatic maceration of mash on a pilot
scale. It was shown that the chemical compositions, sensory properties, and total
yield (~85%) of juice were similar for PEF and enzymatic maceration–assisted
processes; however, PEF treatment resulted in an enhanced release of nutritionally
valuable phenolics into the juice and retained genuine pectin quality. It allows sus-
tainable pomace utilization and offers additional commercial benets (Schilling et
al. 2008a,b). It was shown that the overall composition of juice (pH; total soluble sol-
ids; total acidity; density; sugar, malic acid, and pectin contents; and nutritive value
with respect to polyphenol contents and antioxidant capacities) obtained by pressing
of PEF-treated (E = 1–5 kV/cm) mash did not signicantly differ from that of the
untreated control samples (Schilling et al. 2007). The effects of PEF treatment at E =
450 V/cm and the size of apple mash on juice yield, polyphenolic compounds, sugars,
and malic acid were recently reported by Turk et al. (2010a). Juice yield Y increased
signicantly after PEF treatment of the large mash (Y = 71.4%) as compared with the
small mash (45.6%, control). The acid–sweetness balance was not altered by PEF for
the large mash; however, a decrease in native polyphenol yield after PEF treatment
was observed (control, 9.6%; treated, 5.9% for the small mash).
The effects of PEF treatment (at 400 V/cm) on the characteristics of apple juice
(turbidity, polyphenolic content, and antioxidant capacities) were recently studied
(Grimi et al. 2011). PEF pretreatment was accompanied by a noticeable improvement
in juice clarity, an increase of the total soluble matter and polyphenol contents, and
intensication of the antioxidant capacities of juice. Most of these effects (juice clar-
ity and antioxidant contents) were more pronounced for the treated whole apples than
for untreated whole apples and PEF-treated apple slices. Moreover, the evolution
of apple browning before and after PEF treatment was more pronounced in whole
samples (Grimi et al. 2011).
The possibility of PEF application (at 15 kV/cm) for improvement of pectin extrac-
tion from apple pomace was recently reported (Yin et al. 2009). The PEF technique
was compared with use of chemical additives and ultrasonic and microwave-assisted
extraction techniques; it was concluded that the PEF-assisted technique gave the
highest yield (14.12% pectin) and was the most effective method for pectin extraction
from apple pomace.

55Pulse Electric Field-Assisted Extraction
2.3.1.7 Grapes
Electroporation of wine grapes is an alternative nonthermal process leading to
prudent extraction of colorants and valuable constituents. Praporscic et al. (2007a)
investigated the quantitative (juice yield) and qualitative (absorbance and turbid-
ity) characteristics of juices during the expression of white grapes (Muscadelle,
Sauvignon, and Semillon). The experiments were carried out at an expression pres-
sure of 5 bars, using a laboratory compression chamber equipped with a PEF treat-
ment system. A PEF with strength E = 750 V/cm and total treatment duration t
PEF
=
0.3 s was applied. The PEF treatment resulted in an increase in the nal juice yield
(Y
f
) of up to 73–78% as compared with Y
f
≈ 49–54% for the untreated grapes. A
rather noticeable decrease of absorbance and turbidity was observed as a result of
PEF treatment for all the studied white grape varieties. Later on, Grimi et al. (2009b)
showed that PEF treatment enhanced the compression kinetics and extraction of
polyphenols from Chardonnay grapes.
The effects of PEF pretreatment of grape skins on the evolution of color inten-
sity, anthocyanin content, and total polyphenolic index during vinication of red
grapes (Tempranillo, Garnacha, Mazuelo, Graciano, Cabernet Sauvignon, Syrah,
and Merlot) was investigated. It was shown that these parameters increased in the
nal wine when the electric eld strength was increased from 2 to 10 kV/cm (López
et al. 2008a,b; Puértolas et al. 2010a). Lopez et al. (2009c) studied the application of
PEF treatment (5 kV/cm, 50 pulses) to destemmed, crushed, and slightly compressed
grape pomace (skins, pulp, and seeds) of Cabernet Sauvignon grapes. The applica-
tion of PEF treatment to the pomace before the process of vinication produced
freshly fermented wine that has richer color intensity, more anthocyanin and tan-
nin contents, and showed better visual characteristics. PEF treatment permitted to
reduce the maceration time during vinication of Cabernet Sauvignon grapes from
268 to 72 h. PEF treatment was shown to be more effective in terms of preserv-
ing color intensity and phenolic content than the enzymatic method (Puértolas et
al. 2009). Phenolic extraction during fermentation of the red grapes with continu-
ous PEF system was tested at the pilot-plant scale. The obtained data evidenced the
attractiveness of this PEF-assisted technology at the commercial scale (Puértolas et
al. 2010a,b,c,d,e). Moreover, it was demonstrated that PEF processing of Cabernet
Sauvignon grapes allowed bottling of wines with better characteristics (Folin–
Ciocalteu index, color intensity, polyphenol concentrations) using shorter maceration
times (Puértolas et al. 2010b,c). It was also reported that PEF application increased
the antioxidant activity of extracts from grape by-products (i.e., two-fold higher
than in the control extraction) (Corrales et al. 2008). The other aspects and potential
applications of PEF technology in the winemaking industry were recently reviewed
by Puértolas et al. (2010e)
2.3.1.8 Oil- and Fat-Rich Plants
Guderjan et al. (2005, 2007) reported the application of PEF treatment for improve-
ment of recovery and quality of oils extracted from oil-rich plants. PEF treatment
was tested on maize, olives, soybeans, and rapeseeds. A modied PEF-assisted (at
E = 0.6 kV/cm) process scheme was used, which allowed obtaining a high yield of

56 Enhancing Extraction Processes in the Food Industry
maize germ oil (up to 88.4%) with increased amounts of phytosterols (up to 32.4%).
The oil yield of fresh olives increased by 6.5–7.4%, and the amount of genistein and
daidzein isoavonoids in soybeans increased by 20–21% in comparison to the refer-
ence samples (Guderjan et al. 2005). The higher oil yield and higher concentrations
of tocopherols, polyphenols, total antioxidants, and phytosterols were obtained for
the oil extracted from PEF-treated (at 3 kV/cm) rapeseeds (Guderjan et al. 2007).
The impact of PEF application at eld strength E = 100–2500 V/cm on cell per-
meabilization of coconut was reported by Ade-Omowaye et al. (2000). They showed
that optimal PEF treatment resulted in 20% increase in milk yield, and a combina-
tion of PEF and centrifugation steps resulted in approximately 22% reduction of the
drying time as compared with the untreated samples.
2.3.1.9 Other Vegetable and Fruit Tissues
PEF treatment was also applied to other tissues, such as red bell pepper and paprika
(Ade-Omowaye et al. 2001, 2003), fennel (El-Belghiti et al. 2008), chicory (Loginova
et al. 2010), alfalfa (Gachovska et al. 2006, 2009b), and red cabbage (Gachovska et
al. 2010). Ade-Omowaye et al. (2001) studied the impact of PEF treatment at 1.7 kV/
cm on yield and quality parameters (pH, soluble solids [Brix], total dry matter, color,
total carotenoids [as β-carotene], and vitamin C) of juice obtained from paprika. The
results were compared with those obtained for juice from enzymatically treated or
untreated paprika mash. It was shown that the quality of juice from the PEF-treated
paprika was well comparable with that of the enzyme-treated or untreated juice,
and both PEF and enzymatic treatments resulted in approximately the same (about
9–10%) increase in juice yield. However, the amount of β-carotene extracted into the
juice was more than 60% for PEF treatment as compared to about 44% for enzymatic
treatment (Ade-Omowaye et al. 2001).
The benets of PEF application for the enhancement of soluble matter extraction
from chicory were recently demonstrated (Loginova et al. 2010). Chicory (Cichorium
intybus) roots contain many useful components, such as sucrose, proteins, and inu-
lin. Note that inulin is used for the production of high-quality dietary foods or sugar
substitute in tablets (Franck 2006). The thermally accelerated extraction of soluble
solids from chicory roots is very similar to that used for sugar production from sugar
beets (Berghofer et al. 1993). PEF treatment with a eld strength 100–600 V/ cm,
duration of 10
–3
–50 s, and temperature of 20–80°C was applied (Loginova et al.
2011). The activation energy of thermal damage was rather high (W
τ
≈ 263 kJ/mol);
however, it could be noticeably reduced to W
τ
= 30–40 kJ/mol by application of PEF
treatment. Moderate electric power consumption (Q < 10 kJ/kg) at room temperature
demands application of a relatively high electric eld strength (E = 400–600 V/cm);
however, the value of E noticeably decreases as temperature increases. PEF pretreat-
ment noticeably accelerated diffusion even at low temperatures within 20–40°C.
The proposed technique appears to be promising for future industrial applications of
“cold” soluble matter extraction from chicory roots (Loginova et al. 2010).
PEF-assisted juice extraction from alfalfa mash was studied in Gachovska et al.
(2006). Each PEF treatment at 1500 V/cm was followed by pressure application.
PEF treatment signicantly increased extraction of juice (by 38%), dry matter, pro-
tein, and mineral contents compared with untreated samples. It was reported that

57Pulse Electric Field-Assisted Extraction
PEF technology can be efciently applied for extraction of anthocyanins from red
cabbage (Gachovska et al. 2010). PEF treatment of red cabbage at E = 2.5 kV/cm
enhanced by 2.15 times the total anthocyanin extracted in water (Gachovska et al.
2010) and yielded higher proportions of nonacylated anthocyanins (Gachovska et al.
2010).
2.3.2 BiosuspEnsions
Disruption of some microorganisms is a very important step in industrial extraction
of valuable proteins, cytoplasmic enzymes, and polysaccharides, which are present
inside the cells. Moreover, it is possible to extract the valuable proteins in cultures
of recombinant host cells (Saccharomyces cerevisiae, E. coli) containing foreign
genes. Important medical materials can be synthesized in such cells (Ohshima
1992; Rokkones et al. 1994). However, extraction of intracellular proteins is not an
easy task and requires application of special techniques for cell disruption and for
purication.
2.3.2.1 Cell Disruption Techniques
The existing cell disruption techniques are based on the application of different treat-
ments: mechanical (high-pressure homogenization [HPH], wet milling), chemical
(organic solvents, enzymes, detergents), and physical (sonication, freeze–thawing,
electrically-assisted treatment). The successful recovery of intracellular products
involves the preservation of their contents and removal of cell debris (Engler 1985;
Harrison 1991; Chisti 2007; Peternel and Komel 2010).
Thermal treatment at T > 50°C may result in damage of yeast membranes, and
also causes denaturation and degradation of intracellular proteins and DNA (Chisti
2007). Mechanical methods are most appropriate for the large-scale disruption of
cells and allow high recovery of intracellular material. However, they are restricted
by temperature elevation, they require high power consumption and multiple passes
with supplementary cooling, and their nal products contain large quantities of cell
debris (Brookman 1974; Engler 1985; Lovitt et al. 2000; Middelberg 2000; Wuytack
et al. 2002). Cryogenic grinding at –196°C is a promising technology for protein
release, which has allowed a nearly 100% release of soluble protein from yeasts (S.
cerevisiae), with a small degree of protein denaturation (≈18%); however, this method
was inefcient for DNA release (Singh et al. 2009).
Ultrasonication-assisted methods are restricted by heat generation, high costs,
and extraction yield variability, as well as by generation of free radicals (Bar 1987;
Riesz and Kondo 1992). Chemical methods are rather expensive, usually result in
low recovery of intracellular material, cause protein degeneration, and require addi-
tional purication in the downstream processes (Harrison et al. 1991; Tamer et al.
1998). Detergent-based methods are very sensitive to cell type, pH, ionic strength,
and temperature, and may denature proteins or destroy their activity and functions
(Gough 1988; Cordwell 2008; Patel et al. 2008). Biological, autolysis, and enzy-
matic methods are rather expensive and may affect protein stability. Moreover, they
pre sent a potential problem in that the susceptibility of cells to the enzyme can be
dependent on the state of the cells (Salazar and Asenjo 2007; Chisti 2010).

58 Enhancing Extraction Processes in the Food Industry
2.3.2.2 PEF Application for Killing and Disruption of Microorganisms
Nowadays there exist many examples of PEF application for killing and disrup-
tion of microorganisms (Grahl and Märkl 1993; Barbosa-Cánovas et al. 1998).
Numerous studies have investigated the effect of PEF application on electrofusion
of cells and transport of nanoparticles or biopolymers across the cell wall into the
recipient cells (Van Wert and Saunders 1992; Jen et al. 2004; Pakhomov et al. 2010).
Electroporation-assisted extraction from biocells is expected to be highly selective
with respect to low and high molecular weight intracellular components (Ohshima
et al. 2000), and promising for the recovery of homogeneous and heterogeneous
intracellular proteins having wide biotechnological applications (Ganeva et al. 1999,
2001, 2003; Suga et al. 2006, 2007). The supplementary attractivity of the PEF-
assisted method is related to the fact that this method is nonthermal and is expected
to have a small inuence on the cell wall.
However, the efciency of PEF-assisted extraction in its application to biosus-
pensions may be dependent on multiple factors. The efciency of electroporation
in suspensions may be governed by cell shape and orientation, cell type and strain,
physiological state of cells (age of culture and temperature of cultivation), and state
of cell aggregation (Wouters and Smelt 1997), as well as suspension properties such
as electrical conductivity, salinity, and pH; the presence of surfactants; cell density;
and others (Barbosa-Cánovas et al. 1998; Susil et al. 1998; Pavlin et al. 2002).
It was shown that leakage of cytoplasmic ions during PEF application inuences
the ionic concentration of the medium and its electrical conductivity (Eynard et al.
1992; Kinosita and Tsong 1997; El Zakhem et al. 2006a,b). The leakage of the intra-
cellular components after PEF application was accompanied by decrease in sizes
of S. cerevisiae and E. coli cells (El Zakhem et al. 2006a,b). The conductometric
approach was used for continuous monitoring of the degree of cell damage (S. cere-
visiae and E. coli cells); it was applied for studying the effects of temperature and
surfactant on inactivation efciency (El Zakhem et al. 2006a,b, 2007).
At high concentration of cells in suspension, PEF disruption efciency was found
to be affected by formation of large aggregates (Zhang et al. 1994; El Zakhem et
al. 2006b; Calleja 1984). The possibility of formation of a “pearl chain,” in which
the cells are in very close contact with each other, was described by Zimmermann
etal. (1986, 1992). It was experimentally demonstrated (El Zakhem et al. 2006b)
in S.cerevisiae suspensions that intact cells have a negative charge, as compared
with the positive charge of the damaged cells. Thus, PEF treatment can induce an
electrostatic attraction between intact and damaged cells, and the formation of large
aggregates. In principle, this effect may facilitate the PEF-induced damage due to
the formation of “equivalent cells” of larger volume, or may protect cells against
PEF-induced damage (Zhang et al. 1994). However, incomplete damage of cells
inside the clusters is also possible; it can occur because of the formation of low-
conductive cores (consisting of damaged cells) enveloping a surface of intact cells
inside a oc. Moreover, theoretical calculations predict the dependence of induced
transmembrane potential on cell density and arrangement (Susil et al. 1998; Pavlin
et al. 2002), and that higher voltage amplitude or longer pulse duration is required to
cause the same poration effects if cells are in a cluster (Joshi et at. 2008).

59Pulse Electric Field-Assisted Extraction
The efciency of electroporation of PEF-treated cells may be increased by the
addition of supplementary chemical reagents and nanoparticles. Improvement
of the damage efciency in suspensions by the addition of surfactants, peptides,
dimethyl sulfoxide, or polylysine has been previously reported (Melkonyan et al.
1996; Diederich et al. 1998; Tung et al. 1999; El Zakhem et al. 2007). The use of
nanotubes for enhancement of cell electroporation was recently discussed by sev-
eral investigators (Rojas-Chapana et al. 2004; Yantzi and Yeow 2005; Raffa et al.
2009). Owing tothe so-called lightning rod effect, the nanotubes have the ability to
strongly enhance the electric eld at the tube ends, which makes them ideal for local-
ized electroporation. It was demonstrated that nanotubes can be used as nanotools,
enabling electropermeabilization of cells at rather low electric elds (40–60 V/cm)
(Raffa et al. 2009). The pulsing protocol (electric eld strength, pulse shape, pulse
length, total time of treatment, temperature) is very important. Note that, typically,
inactivation and disruption of microorganisms requires high critical electric elds
(E > 2–5kV/ cm). It presumably reects relatively small cell sizes—for example,
between 2 and 15 μm for S. cerevisiae (near spherical shape) and 0.4–0.6 μm diam-
eter and2–4 μm length for E. coli (rod-like shape) (Bergey 1986).
2.3.2.3 Yeasts
The commonly reported values of eld strength E needed for disintegration of mem-
branes in S. cerevisiae yeast cells by short pulses of microsecond duration are rather
high, typically E > 7.5 kV/cm (Zhang et al. 1994). However, smaller electric elds
can also affect the structure of yeast cells at a long duration of PEF treatment. For
instance, a noticeable damage in yeast cells at E < 7.5 kV/cm was observed at a long-
duration PEF treatment (>1 s) (El Zakhem et al. 2006a,b).
The release of proteins in a PEF-treated aqueous suspension of S. cerevisiae cells
was observed for relatively low (below 10 kV/cm) PEF (Ohshima et al. 1995). No cell
wall damage related to PEF application was observed by scanning electron micros-
copy, and the concentration of protein was found to increase with the increase in
electric eld strength E (0–18 kV/cm) during treatment. However, the maximal yield
of PEF-assisted extraction was only 5% of that obtained using glass bead homogeni-
zation. It was concluded that some intracellular proteins could be released through
the pores (induced by PEF treatment) selectively, depending on the PEF protocol.
PEF application (at E = 3–4.5 kV/cm) to yeast suspensions resulted in a high
extraction yield of intracellular proteins and enzymes, with their functional activ-
ities preserved (Ganeva and Galutzov 1999; Ganeva et al. 2001, 2003). The spe-
cic activities of the electroextracted enzymes were higher than those of enzymes
obtained by mechanical disintegration or enzymatic lysis (Ganeva et al. 2003).
The highest extraction yield of proteins, glutathione reductase, 3-phosphoglycerate
kinase, and alcohol dehydrogenase was observed for supplementary pretreatment by
dithiothreitol (a reducing agent), and maximal yield was observed 3–8 hours after
PEF application (Ganeva and Galutzov 1999). Electropulsing (4–4.5 kV/cm and 2
ms pulse duration) allowed effective extraction of the enzyme β-galactosidase from
the yeast Kluyveromyces lactis with 75–80% yield within 8 h after PEF application
(Ganeva et al. 2001). The extraction efciency was strongly dependent on the growth

60 Enhancing Extraction Processes in the Food Industry
phase of yeast cells and salinity of the solution in the postpulse incubation period
(Ganeva and Galutzov 1999; Ganeva et al. 2001). It was shown that high yields of
intracellular enzymes from yeast can be obtained through PEF treatment of the ow-
ing suspensions. The maximal yield of enzymes (hexokinase, 3-phosphoglycerate
kinase, and glyceraldehyde-3-phosphate dehydrogenase) from S. cerevisiae and of
β-galactosidase from K. lactis was reached within 4 h. The proposed ow method
permitted treatment of large volumes and treatment of at least 20% wet weight sus-
pensions (Ganeva et al. 2003).
PEF treatment of S. cerevisiae at 5 kV/cm allowed attaining a high conductivity
disintegration index, Z ≈ 1, with higher amounts of released peptides and proteins
than nucleic acid bases (El Zakhem et al. 2006b). However, in PEF-treated suspen-
sions of wine yeast cells (S. cerevisiae bayanus strain DV10), a relatively small
release of proteins was observed even at a high index of Z ≈ 0.8 (Shynkaryk et al.
2009). Moreover, it was demonstrated that high levels of membrane disintegration
(Z> 0.8) in these yeasts require a rather strong PEF treatment (at E = 10 kV/cm using
2 × 10
5
pulses of 100 μs). Thus, the efciency of PEF-assisted extraction was depen-
dent on the yeast strain. It can reect the presence of hard cell walls in addition to cell
membranes that can restrict extraction of intracellular compounds. More effective
extraction of high molecular weight contents (e.g., proteins) from electrically resis-
tant strain requires more powerful mechanical disintegration of cell walls, which
is provided by high-voltage electrical discharges (HVED) and HPH techniques. In
principle, HPH permitted better extraction than HVED (Loginov et al. 2009; Liu et
al. 2010). However, a synergistic enhancement of protein release from yeasts can be
attained using combined disruption techniques. It was shown that a combination of
HVED and HPH techniques allowed reaching a high level of protein extraction from
wine yeast cells (S. cerevisiae bayanus, strain DV10) at lower pressures or smaller
number of passes through the homogenizer (Shynkaryk et al. 2009).
2.3.2.4 Escherichia coli
The commonly reported values of eld strength E needed for disintegration of mem-
branes in E. coli cells by short pulses of microsecond durations are even higher
than for S. cerevisiae, which typically require E = 10–35 kV/cm (Grahl and Märkl
1996; Aronsson et al. 2001; Aronsson and Rönner 2005; Amiali 2006; Bazhal et al.
2006). However, a noticeable permeabilization of the membranes in E. coli cells was
observed at signicantly smaller elds (E = 1.25–3.75 kV/cm) (Eynard et al. 1998).
Note that PEF-induced orientation of rod-like cells in external electric elds can
facilitate their electropermeabilization (Eynard et al. 1998).
PEF treatment (10 kV/cm, with a needle-plate electrode geometry) of genetically
engineered E. coli suspension allowed the effective release of β-glucosidase and
α-amylase (Ohshima 2000). It was noted that PEF treatment could easily disrupt the
outer membrane, but it was difcult to disrupt the cytoplasmic membrane simulta-
neously, and it was concluded that PEF treatment is useful for easy selective release
of periplasmic proteins (Ohshima 2000).
Experimental studies on PEF treatment of the owing concentrated aqueous sus-
pensions of E. coli (1 wt.%) at E = 5–7.5 kV/cm and medium temperatures within
30–50°C were done by El Zakhem et al. (2007, 2008). A noticeable disruption of

61Pulse Electric Field-Assisted Extraction
cells was observed at PEF treatment time (t
PEF
) within 0–0.2 s and thermal treatment
time (t
T
) within 0–7000 s. It was shown that disruption of E. coli was accompanied
by decrease in cell size and release of intracellular components. Absorbance analysis
of supernatant solutions evidenced the leakage of nucleic acids. The electrical con-
ductivity disintegration index Z was monitored in a continuous mode in the course of
PEF–thermal treatment through electrical conductivity measurements (Figure 2.12).
Thermal treatment alone at T = 30–50°C was ineffective for disruption of E. coli
cells and required a long treatment time (t
T
>> 1 h). For example, 1 h of thermal
treatment resulted in increases in electrical conductivity disintegration index Z of
up to ≈0.02, ≈0.28, and ≈0.66 at temperatures of 30°C, 40°C, and 50°C, respectively
(Figure 2.12). Moreover, there was an evident synergism between the simultaneously
applied electrical and thermal treatments. The electrical conductivity disintegration
index Z after 1 h of PEF and thermal treatments reached ≈0.22, ≈0.83, and ≈0.99
at temperatures of 30°C, 40°C, and 50°C, respectively (Figure 2.12). The observed
behavior can be explained by the increased uidity of cell membranes and possible
phase transitions inside them (Stanley 1991). A synergy between PEF and thermal
treatments was also observed in E. coli in inactivation experiments with higher elec-
tric elds (Zhang et al. 1995; Pothakamury et al. 1996; Aronsson et al. 2001; Bazhal
et al. 2006).
It was shown that surfactant additives (Triton X-100) additionally improved dis-
ruption of cells in E. coli suspensions (El Zakhem et al. 2007, 2008). The inu-
ence of the surfactant on E. coli disruption efciency was explained by changes
in the membrane uidity properties and changes in the state of cell aggregation in
1000 2000 3000 4000 5000 6000 7000
1
T = 50˚C
T = 30˚C
, - PEF- thermally treated, C
s
= 1 wt.%
, - PEF- thermally treated, C
s
= 0 wt.%
, - ermally treated, C
s
= 0 wt.%
0.8
0.6
0.4
0.2
0
0 0.05
PEF treatment time (t
PEF
), s
Disintegration index (Z
C
)
t
T
, s
0.1 0.15 0.2
FIGURE 2.12 The electrical conductivity disintegration index Z
C
versus effective PEF
treatment time (t
PEF
) and thermal treatment time (t
T
) at different temperatures T. C
s
is the
surfactant concentration (wt.%). PEF treatment was done at electric eld strength E = 5 kV/cm
and pulse duration t
i
= 10
−3
s. (From El Zakhem, H. et al., Int J Food Microbiol 120, 259–265,
2007. With permission.)

62 Enhancing Extraction Processes in the Food Industry
suspension (El Zakhem et al. 2007). Addition of a surfactant resulted in enhanced
aggregation and formation of an “equivalent cell” of larger size that can enhance
the PEF damage efciency (Zimmermann et al. 1986). The disruption efciency of
cells in E. coli suspensions was also noticeably improved by the addition of organic
(citric, malic, and lactic) acids in small concentrations (≤0.5 g/L), and an 8 log cycle
reduction was reached by using 0.375 g/L of lactic acid (El Zakhem et al. 2008).
Lactic acid can be efciently used in food-related applications, and it is well known
as an effective permeabilizer and disintegrating agent of outer membranes in gram-
negative bacteria, including E. coli (Alakomi et al. 2000; Theron and Lues 2011). It
was assumed that lactic acid may act as a very effective potentiator of PEF effects in
membranes of E. coli cells (El Zakhem et al. 2008).
2.4 PEF PILOT-SCALE EXPERIMENTS AND APPLICATIONS
The recent applications of PEF treatment in the food industry are mainly restricted
by attempts on gentle microbial inactivation and pasteurization of pumpable foods
(e.g., milk, fruit juices) (Lelieveld et al. 2007) and extraction of cellular constituents
from the tissues (Vorobiev and Lebovka 2008).
2.4.1 somE ExamplEs of rElatEd rEcEnt patEnts
Doevenspeck (1991) has patented an electric-impulse method for treating substances
located in an electrolyte, and Bushnell et al. (2000) have patented a pumpable serial-
electrode treatment system for deactivating organisms in a food product. Eshtiaghi
and Knorr (1999) and Arnold et al. (2010) have patented methods for treating sugar
beets. Vorobiev et al. (2000) have patented a PEF-assisted process for acceleration
of extraction from tissues, where PEF treatment is combined with mechanical press-
ing. Ngadi et al. (2009) have presented the invention of a PEF-assisted method for
enhancement of extraction of phytochemicals from plant materials, wherein PEF
treatment and pressing are applied and the PEF treatment could be accomplished in
a unique treatment chamber.
2.4.2 pastEurization and rEgulation of microBial staBility
For uid food products, several fundamental works were done for elucidation of
the association between laboratory-, pilot plant–, and commercial-scale applications.
The pilot scale continuous scheme was used for the study of the relationship between
PEF protocol parameters (power consumption 0–300 kJ/kg, electric eld strength
25–70 kV/cm, square wave pulse width 0.05–3 μs, and initial product temperature
4–20°C) and efciency of Salmonella enteritidis inactivation in aqueous solutions
(Korolczuk et al. 2006). A 3d computational model of uid dynamics in a pilot-scale
PEF system with colinear electrodes was developed by Buckow et al. (2010). Note
that PEF is a more energy-efcient process than thermal pasteurization, and it would
add only US$0.03–US$0.07/L to the nal food costs (Ramaswamy et al. 2008).
Different types of pilot plant–scale PEF systems were developed for pasteuriza-
tion and regulation of microbial stability in pumpable foods such as yogurt, milk,

63Pulse Electric Field-Assisted Extraction
and juices (Barbosa-Canovas et al. 2000). A pilot plant–scale PEF continuous pro-
cessing system integrated with an aseptic packaging machine was used as a non-
thermal tool for effective microbial inactivation of fresh orange juice at a ow rate
of 75–150 liters/h (Qiu 1997, 1998). The PEF-treated and aseptically packaged fresh
orange juice demonstrated the feasibility of use of the PEF technology to extend
product shelf lives with very little loss of avor, vitamin C, and color (Qiu et al.
1997). A synergistic effect of temperature and PEF inactivation was also observed
in a pilot plant PEF unit with the ow rate of 200 liters/h (Wouters et al. 1999). The
applications of pilot plant PEF facilities (at 16.4–37.3 kV/cm) in the batch and contin-
uous ow modes for inactivation of microorganisms capable of secreting lipases in
milk and dairy products were discussed by Bendicho et al. (2002). PEF processing of
yogurt-based products by using the OSU-2C pilot plant scale system was studied by
Evrendilek et al. (2004). Mild heat (at 60°C for 30 s) combined with PEF treatment
(at 30 kV/cm electric eld strength and 32 μs total treatment time) did not affect the
main characteristics (color, pH, and °Brix) of the product, and prevented the growth
of microorganisms and decreased the total mold and yeast count in yogurt-based
products during their storage at 4°C and 22°C.
A pilot plant–sized PEF treatment (at electric eld strength 25–37 kV/cm, pulse
width 1.84 μs, power consumption 11.9 J/ml per pulse, and total treatment time vary-
ing within 54–478 μs) was applied for nonthermal preservation of liquid whole eggs
(Góngora-Nieto et al. 2003). Citric acid (CA) additives were used as color stabiliz-
ers and also for increasing the effectiveness of PEF treatment. It was shown that
the maximum shelf life of PEF-treated liquid whole eggs (at 4°C) was 20 days, and
almost 30 days with 0.15% CA and 0.5% CA, respectively.
The efciency of PEF treatment for pasteurization of apple sauces was demon-
strated in a pilot plant scale by Jin et al. (2009). A system for continuous ow PEF
treatment followed by high-temperature, short-time processing integrated with an
aseptic packaging machine was tested. The PEF treatment system included a co-
eld continuous ow tubular chamber (inner diameter, 0.635 cm), with boron car-
bide electrodes (gap distance between electrodes, 1.27 cm) and high voltage pulse
generator (OSU-6; Diversied Technology Inc., Bedford, MA, USA). The generator
provided bipolar square pulses with 60-kV voltage, maximum peak current of 750 A,
maximum frequency of 2000 Hz, and pulse width of 2–10 μs.
The pilot-scale PEF treatment (45.7 μs at 34 kV/cm) combined with mild heating
(24 s at 67.2–73.6°C) was applied to salad dressing inoculated with Lactobacillus
plantarum 8014, and more than 7 log inactivation was achieved. It was reported that
no L. plantarum 8014 was recovered in the model salad dressing at room tempera-
ture for at least 1 year (Li et al. 2007).
The pilot plant–scale PEF treatment (94 μs mean total treatment time at 35 kV/
cm) was applied for the study of inactivation of E. coli O157:H7 and evaluation of
shelf life of aseptically packaged apple juice and cider (Evrendilek et al. 2000). It
was shown that PEF treatment improved the microbial shelf life of the apple cider
and did not alter its natural food color and vitamin C content. A portable pilot-
scale PEF processing machine was constructed and evaluated in the pasteurization
of apple cider (Jin and Zhang 2005). Different PEF pilot systems for microbial inac-
tivation and pasteurization were developed in the Eastern Regional Research Center,

64 Enhancing Extraction Processes in the Food Industry
Wyndmoor, PA, USA, and the rst commercial application of PEF for pasteurization
of apple cider was reported by Ravishankar (2008).
2.4.3 Extraction
An industrial prototype for starch extraction from potatoes was developed by Propuls
GmbH, Bottrop, Germany (Loefer 2002; Top 2006). The automated ow of pota-
toes came from a feeding funnel with two cross electrodes. After passing the water-
lled electrode section, the electrically treated potatoes were separated from water
with a screw conveyer for further treatment.
A commercial pilot plant–scale PEF mobile device (Karlsruher Elektroporations
Anlage, KEA-Tec, Germany) was contracted for effective treatment of large speci-
mens (e.g., entire sugar beets) in a continuous mode (Schultheiss et al. 2003; Sack et
al. 2005). It consisted of a 300-kV Marx generator operating at 10 Hz and delivering
pulses to a cylindrical reaction chamber with maximal electric eld strength up to 60
kV/cm. This device was used for demonstration of the advantages of PEF treatment for
sugar production. Encouraging results were obtained by several research groups. They
revealed an industrial interest in PEF pretreatment, and a semi-industrial–scale equip-
ment was built for PEF-assisted extraction (Sack et al. 2010). The equipment allowed
handling a throughput of up to 1 t/h, with a power consumption about 15 kW·h/t. Both
red and white wine grapes were processed using this equipment (Sack et al. 2010).
The efciency of PEF treatment (at E = 400 V/cm and total treatment time of 50
ms) for sugar extraction from sugar beets was justied using a pilot countercurrent
section extractor (Loginova et al. 2011). Cossettes were prepared from sugar beets
by using industrial knives, and the temperature was varied between 30°C and 70°C.
The possibility of PEF-assisted cold (at 30°C) and moderate thermal (50–60°C)
sugar extraction was shown.
The good industrial potential of PEF-assisted apple juice expression was conrmed
on laboratory and pilot scales using belt-press equipment (Jaeger et al. 2008; Grimi et
al. 2008). Figure 2.13 shows a scheme (a) and a photo (b) of a pilot belt press recently
used for PEF-assisted expression of sugar beets (Grimi et al. 2008; Grimi 2009). The
pilot experiments were done for untreated and PEF-treated sugar beet slices of dif-
ferent sizes: S1 (0.045 mm
3
), S2 (47.5 mm
3
), S3 (280 mm
3
), and S4 (1050 mm
3
). The
obtained results conrmed the amelioration of juice yield and purity on application of
PEF pretreatment. It was concluded that the size of particles treated by PEF should be
optimized for attaining the maximal yield and better purity of the juice.
A pilot plant–scale PEF treatment (at E = 2, 5, and 7 kV/cm) for improving extrac-
tion of anthocyanins and phenols from red grapes (Cabernet Sauvignon, Syrah, and
Merlot) during the maceration-fermentation step was investigated by Puértolas et al.
(2010a). PEF treatment was done in a colinear continuous treatment chamber, and
the maximum PEF treatment capacity was about 1000 kg/h (Figure 2.14). The PEF
generator (Modulator PG; ScandiNova, Uppsala, Sweden) provided square wave-
form pulses at 30 kV voltage, maximum peak current of 200 A, maximum frequency
of 300 Hz, and pulse width of 3 μs. The reported energy requirements of the pro-
cess were rather low (6.76–0.56 kJ/kg), and the PEF-assisted technology allowed to
decrease the duration of maceration during vinication or to increase the quantity

65Pulse Electric Field-Assisted Extraction
of anthocyanins and phenolic compounds in the wine. For example, in experiments
with PEF treatment of Cabernet Sauvignon at 5 kV/cm, the maximum concentrations
of anthocyanins and total phenols were 34% and 40% higher than in untreated con-
trol samples, respectively (Puértolas et al. 2010a). Similar pilot plant–scale studies
of the inuence of PEF treatment of grape berries on the evolution of chromatic and
phenolic characteristics of Cabernet Sauvignon red wines were done by Puértolas
et al. (2010c). Better chromatic characteristics and higher phenolic content were
observed in PEF-treated wine samples during aging in American oak barrels and
subsequent storage in bottles. It evidenced that PEF-assisted processing is a promis-
ing enological technology for the production of aged red wines with high phenolic
content (Puértolas et al. 2010b).
Comparative laboratory- and pilot plant–scale studies of PEF and thermal pro-
cessing were done for apple juice (Schilling et al. 2008a) and apple mash (Schilling
(a)
(b)
Feeding
Upper belt
Lower belt
Cake
J
J: Juice extract
J
J
J
+
-
FIGURE 2.13 (a) A scheme and (b) a photo of a pilot belt press recently used for PEF-
assisted expression from the sugar beets. (From Vorobiev, E. and Lebovka, N., Food Eng Rev
2, 95–108, 2010. With permission.)

66 Enhancing Extraction Processes in the Food Industry
et al. 2008b). It was shown that juice composition was not affected by PEF treatment;
however, PEF treatment of apple mash enhanced the release of nutritionally valuable
phenolics into the juice (Schilling et al. 2008b). The observed browning of PEF-
treated juices provided evidence of residual enzyme activities. The different combi-
nations of preheating and PEF treatment had a synergistic effect on peroxidase and
polyphenoloxidase deactivation. For example, a 48% deactivation of polyphenoloxi-
dase activity was achieved on a plant scale on preheated (to 40°C) and PEF-treated
(at 30 kV/cm, 100 kJ/kg) juices (Shilling et al. 2008a).
PEF treatment (1000 V/cm, 200 Hz, and 100 μs pulse duration) was applied to
French cider apple mash pumped into a collinear treatment chamber at the ow rate
of 280 kg/h (Turk at al. 2009). Juices were recovered continuously under a single
belt press. PEF treatment of mash increased the juice yield by approximately 4%.
Juice from the treated mash had a better color than that from the control. The overall
chemical composition of the treated juices showed no differences from their respec-
tive controls.
Recently, Turk and colleagues (Turk 2010; Turk et al. 2010b) conrmed their
results obtained with French cider apple mash on an industrial scale (ow rate of
4500 kg/h). PEF (E = 650 V/cm and t
PEF
= 23.2 ms) application permitted a 5.2%
increase in juice yield. The energy provided (3.5 W·h/kg of mash) contributed to
the increase in dry matter of the marc from 19.8% to 22.5%. The reduction in the
quantity of water to be evaporated during the drying process was estimated as
12.1W·h/ kg. Consequently, the total energy savings from pressing/drying would be
approximately 8.6 W·h/kg of mash. The juices treated by PEF were signicantly less
turbid and had more intense odor, savor, and avor.
(a)
(b)
Flow Flow
Ground GroundInsulator Insulator
High
voltage
2 cm
2.4 cm 2 cm
1 1
2 23 3
4 4
7 7
6 6
5 5
FIGURE 2.14 The colinear treatment chamber used at a pilot plant for PEF processing of
red grapes. (a) The treatment chamber consisted of three cylindrical electrodes (stainless
steel) separated by two methacrylate insulators. The central electrode was connected to high
voltage and two others were grounded. (b) The distribution of the electric eld strength E was
not uniform. An example of E distribution simulated by method of nite elements for 14.2 kV
input voltage is shown. The value of E changes from the weakest (1 kV/cm) to the strongest
(7kV/cm). (From Puértolas, E. et al., J Food Eng, 98, 120–125, 2010a. With permission.)

67Pulse Electric Field-Assisted Extraction
2.4.4 food safEty aspEcts
PEF treatment of foods at a relatively moderate electric eld strength (<50 kV/cm)
can affect the integrity of cell membranes; however, such electric elds are still
rather low and do not inuence covalent chemical bonds, and do not cause protein
alternation and gelatinization of starch. Many experimental works conrmed the
retention of freshness, color, and nutrients in food products after PEF treatment.
The use of PEF treatment is subject to US and EU food regulations; however, its
associated electrochemical processes are still insufciently understood (Smith 2007;
Knorr et al. 2008). Electrochemical reactions at the electrode surfaces may introduce
undesirable effects, which can be avoided by selection of suitable electrodes and PEF
protocols (Morren et al. 2003; Roodenburg et al. 2005a,b; Roodenburg 2007). The
food safety aspects associated with the application of PEF-assisted technologies for
processing of foods were recently discussed by the working group “Food technology
and safety” of the Deutsche Forschungsgemeinschaft Senate Commission on Food
Safety (Knorr et al. 2008) and reviewed by Smith (2007).
2.5 CONCLUSIONS
PEF is a novel method in food processing that is based on disruption of very thin
(≈0.5 nm) membranes in biological cells. The selectivity of disruption was shown
to be very high, and this method practically retains the integrity of cell walls, and
the color, avor, vitamin C content, and important nutrients of food materials. The
PEF method is energetically cost-efcient and nonthermal—that is, the elevation of
temperature related to ohmic heating may be unessential.
However, disruption of cell membranes results in the acceleration of mass exchange
processes in food materials. Recent laboratory experiments demonstrated many prom-
ising examples of the PEF-assisted extraction of juices, sugars, colors, polyphenolic
substances, and oils from solid foods (sugar beets, apples, grapes, etc.). PEF treat-
ment also poses unique possibilities for extraction of valuable proteins, cytoplasmic
enzymes, and polysaccharides from cells in suspensions, and opens new prospects for
the production of valuable proteins in cultures of recombinant host cells (S. cerevi-
siae, E. coli). The rst important steps for practical implementations of PEF-assisted
technologies at the pilot plant scale have already been done. Future technologies will
allow overcoming the difculties associated with mechanical, thermal, or chemical
pretreatments presently used in food processing, and provide a potential method for
production of foods with excellent sensory and nutritional qualities.
ACKNOWLEDGMENTS
The authors thank Dr. N. S. Pivovarova for her help with manuscript preparation.
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