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Green extraction methods of food polyphenols from

vegetable materials
Palash Panja

Green extraction methods are being developed using modern microwave (MW), ultrasound, and pulsed electric field.
technology where less or no organic solvents are used to Smarter applications of combined technologies, such as
minimize environmental and health impacts and to maximize supercritical fluid with ultrafiltration and microwave with
the yield of desired polyphenols by selective extraction. ultrasound, have also enhanced the recovery. Maximum
Advanced methods such as microwave assisted, ultrasound yield of polyphenols in shorter extraction time with less
assisted, pulsed electric field assisted and enzyme assisted amount of solvent ensures lower costs processes. Recent
extractions, as well as pressurized liquid and supercritical fluid developments in extraction methods, such as microwave,
extractions are given more emphasis. The theory behind some ultrasound, and pulsed electric field and enzyme-assisted
advanced extractions methods is described. A brief review of extractions, are the focus of this study. Applying these
applications of extractions from various parts of plants such as advanced methods, researchers have recovered polyphe-
roots, fruits, seeds, leaves, vegetables, barks, etc. are nols from fruit, leaves, roots, vegetables, etc. Theories
provided. behind different techniques and their applications are
discussed here.
Address
Energy & Geoscience Institute, University of Utah, 423 Wakara Way, Extraction methods
Suite 300, Salt Lake City, UT 84108, USA
Various steps are involved to isolate the polyphenols from
Corresponding author: Panja, Palash (ppanja@egi.utah.edu) vegetable materials, including feed preparation, extrac-
tion, purification and drying. Feed preparation is an
essential part of the extraction process. Before putting
Current Opinion in Food Science 2017, 17:xx–yy it into the extractor, the feed is prepared to remove
This review comes from a themed issue on Food Engineering and unwanted materials and to make it suitable for maximiz-
Processing ing extraction efficiency. Depending on the part of the
Edited by José Ricardo Pérez-Correa sample to be extracted, the unnecessary components are
removed. For example, prior to a fruit rind extraction, the
seeds and pulp must be removed before processing. This
way, available volume in the extractor can be used effec-
https://doi.org/10.1016/j.cofs.2017.11.012 tively. Another benefit is to increase the solvent to feed
2214-7993/ã 2017 Elsevier Ltd. All rights reserved. ratio for the same amount of solvent use. Sometimes the
feed must be grounded to increase the surface area for
mass transfer. It is recommended to clean up the food
before mixing with solvent to remove foreign materials
such as soil particles, small stones, etc. In some cases, the
feed is frozen prior to extraction. Softening the feed is
Introduction usually required.
Polyphenols are abundant in natural sources like fruits,
herbs and spices, nuts, roots and vegetables. Human The extraction is the most important step to isolate
health benefits, mainly as antioxidants, attracted polyphenols from the vegetable materials. The technique
researchers to recover them efficiently. Various types of and the solvent are key factors to maximize recovery
food polyphenols or phenolic compounds are identified. selectively, avoiding undesired substances. In traditional
Solvents like water, alcohols (mainly ethanol and metha- methods, simple equipment is used, where often the
nol) are used to extract polyphenols. Heat reflux, macera- quality, quantity and time of extraction are questionable.
tion, Soxhlet extraction, etc. were performed traditionally Over time, these methods have been improved to
where large amount of solvent had been used with longer increase the extraction efficiency and to reduce the
time of extraction. As new technologies emerge, the extraction time. Many modern extraction techniques
extraction methods have become efficient and cleaner have been developed for quick and selective extraction
where products are devoid of organic solvents and with less amount of solvent. A few common techniques of
cheaper in cost. extraction are listed in Table 1.

Total cost of production is reduced significantly by pro- In this article, only a few selective advanced techniques
cess intensification using advanced technology such as are discussed.

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2 Food Engineering and Processing

Table 1 of phytochemicals. Polar solvents such as water, ethanol,

Various extraction methods. acetic acid, etc. are the best to extract polar compounds.
Similarly, nonpolar solvents such as hexane, benzene,
Traditional methods Advanced methods
toluene, etc. are used to extract nonpolar phytochemicals.
Infusion Pressurized liquid extraction
Decoction Supercritical fluid extraction
Maceration Microwave assisted extraction
A special case of PLE is pressurized hot water extraction
Percolation Ultrasound assisted extraction (PHWE), where water is used as solvent at an elevated
Reflux extraction Enzyme assisted extraction temperature and pressure. Being environmental friendly
Soxhlet extraction Pulsed electric field extraction and economically, viable, water is widely used. Consid-
ering that PHWE is performed with liquid water at 2–
20 atm pressure, the potential extraction zone is very
Pressurized liquid extraction (PLE) narrow, which is bounded by 80–180 C in the tempera-
Generally, in all extraction methods, elevated tempera- ture side.
ture enhances the recovery of polyphenols. The high
temperature extraction methods are most effective if PHWE is a very promising and attractive technique for
the polyphenols have a higher endurance to temperature. many reasons. Water is cheap and environmentally
Pressurized liquid extraction (PLE) works on the princi- friendly. Water can be used as a universal solvent. In
ple that the boiling point temperature is proportional to addition to extracting polar substances, water can be used
the pressure. Therefore, the pressure of the extraction to extract less polar or borderline nonpolar substances,
system is increased before raising the temperature, in altering the polarity of water by adjusting the extraction
order to keep the solution in liquid state. Several temperature. The polarity of water at 205 C is the same as
researchers have proven that the solubility of chemicals, the polarity of methanol at 25 C. This implies that water
mainly polyphenols in liquids, is increased in PLE [1–3]. can replace methanol from the polarity perspective.
There are many advantages of PLE, as listed here:
In addition to polarity reduction, viscosity, density and
- Higher amounts of polyphenols are recovered at ele- surface tension of water are also reduced at higher tem-
vated temperature. peratures. Low viscosity and surface tension enhance the
- The process is energy saving, because the sensible heat mass transfer, therefore facilitating the extraction of poly-
of a liquid is less than the heat of vaporization. Hence, phenols from matrices of plant parts. Another way to
less heat is required to increase temperature than to reduce the surface tension is the addition of surfactant
generate vapor. that significantly improves the solubility of polyphenols
- Solvents used in PLE are mainly water and aqueous in water. All these combined effects make PHWE very
alcohols. These solvents are environmentally friendly effective [2,7]. The efficiency of PHWE can be enhanced
and non-toxic. further by adding other solvents and changing the pH of
- Solvents are low cost since a large part is liquid water. water by adding acid or acidic substances. The extractor
- The extraction equipment, mainly the extractor and the of PHW is often pressurized with CO2 and that way it
associated set up, are simple. serves both purposes of increasing pressure and increas-
ing pH. Dissolved CO2 in water makes weak acid (car-
The temperature of PLE is in the range of 50–200 C bonic acid, H2CO3) [3].
[4,5]. Maximum temperature of extraction is dependent
on both the solvent and polyphenols. High temperatures Extraction temperature, pressure, stirring rate, extraction
may degrade active components and dissolve undesired time, sample particle size, pH of water, and the water to
compounds. In addition, the choice of solvents is limited, feed ratio are the key factors that affect the performance
since they should have high auto ignition temperatures of PHWE. A comprehensive list of applications (1999–
and reduced metal corrosiveness at high temperatures 2014) of PHWE for extraction of polyphenols was pre-
and pressures. pared by Vergara Salinas [8].

The procedures and applications of PLE to extract poly- Supercritical fluid extraction (SFE)
phenols are discussed in detail by Vergara-Salinas et al. The critical point of a fluid is a thermodynamic property
[6]. Polarity of solvent changes with temperature, mak- defined mainly by a temperature and a pressure. Above a
ing PLE very effective for selective extraction. Various critical temperature, liquid phase cannot be formed from
solvents such as methanol, ethanol, aqueous methanol, gas phase irrespective of any high pressure. The vapor
aqueous ethanol, acidic aqueous methanol and acidic pressure of the fluid at critical temperature is called
aqueous ethanol, aqueous 1-propanol, aqueous acetone critical pressure. At supercritical condition, that is, above
are commonly used [2]. Following the rule of thumb in the critical point, no liquid-gas phase boundary exists and
the selection of solvents (i.e. ‘like dissolves like’), the consequently no surface tension exists. Fluid behaves
prime considerations are the polarity of solvent and type like a single phase, retaining the properties of gas and

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Food polyphenols from vegetable materials Panja 3

liquid at the same time. At this condition, fluid diffuses applications of supercritical CO2 have been summarized
into the solid matrix like a gas and dissolves active in a recent review article [11]. Optimization of operating
materials like a liquid. These properties are very effective conditions, mainly the temperature, pressure and extrac-
to extract active components from plant parts. This is the tion time, were determined using a response surface
basic principle of supercritical fluid extraction (SCFE). method with central composite rotatable design or Box-
Slight variations in the temperature and the pressure –Behnken design of experiments to extract polyphenols
cause significant changes in properties of supercritical from crocussativus petals [12], fresh frozen tea leaves
fluid. [13] and Propolis [14].

The critical points of solvents can be found in numerous Microwave assisted extraction (MAE)
literature references. The critical temperatures of water, Microwaves are electromagnetic radiation with wave-
methanol, ethanol and acetone are relatively high com- lengths ranging from 1 mm to 1 m with frequencies from
pared to other solvents. The right candidate solvent for 300 MHz (1 m) to 300 GHz (1 mm). The microwave
SCFE is selected by screening various aspects such as assisted extraction method is one of the advanced meth-
safety, hazard, energy requirement, operability, etc. The ods currently used for recovering polyphenols. The
process becomes energy intensive if a solvent of high method is gaining popularity because microwave ovens
critical temperature is selected. A lot of energy is required or customized equipment are easily available at low cost.
to raise the solvent temperature above critical point. Along with many technical applications, the microwave
Therefore, it adds extra energy cost for the plant. oven is an essential kitchen appliance in modern lifestyles
to cook or heat up foods. Easy, rapid and clean use of
In addition to energy cost, higher temperature causes microwave ovens make the process more attractive. It also
degradation of active ingredients and reduces the selec- prevents overheating of food, avoiding browning or car-
tivity. For this reason, water is not considered as a amelization, because the temperature stays around the
potential solvent in SCFE. From a safety point of view, boiling point of the liquid. The principle of heating
flammable solvents are avoided at high temperature. For a solvent by microwave is based on two mechanisms
example, propane, methanol, ethanol have critical tem- [15–17]. The first one is known as dielectric heating,
peratures of 97, 239 and 235 C respectively. Although the caused by rotation of the dipole moment. Molecules
auto-ignition temperatures are high enough (470, 433 and rotate according to dipole moments and randomize
365 C respectively) beyond the extraction temperature, instantly with the frequency of the microwave. This
any leakage from the system can cause a fire hazard from molecular movement causes heating of the solvent.
external source of fire. Generally, these solvents are not The second mechanism is called ionic conduction. Ions
used in SCFE. are aligned with the electromagnetic field such as micro-
wave radiation. The friction between the flow of ions and
The most attractive fluid for SCFE is carbon dioxide. CO2 the rest of the solvent results in heat. Depending on the
is nontoxic, nonflammable, chemically inert, cheap and polarity of the solvent and presence of ions in the solvent,
available in high quality and quantity. The critical tem- both mechanisms can occur simultaneously.
perature of CO2 is very low (31 C), which is close to
ambient temperature. Therefore minimal or no heat is Selection of solvents in MAE is very important. In other
required to reach the critical temperature. Although its extraction methods such as PLE, solvents are chosen
critical pressure is high (73 atm), it is still suitable for lab based on their affinity to active components. In case of
scale or pilot plant operations. As discussed earlier, the MAE, the affinity is not the single factor. The ability to
supercritical fluid has more capacity to contain active absorb microwave radiation is the primary factor for the
material as part of liquid behavior and it has more diffu- solvents. Many solvents, such as hexane, dichloro-
sivity for having gas-like behavior. Another advantage of methane and toluene, are transparent to microwaves.
CO2 in SCFE is the easy separation of extracted materi- That means these solvents cannot be heated with micro-
als. Exposing gas to room conditions (25 C, 1 atm), CO2 is waves. Solvents such as dimethyl sulfoxide (DMSO),
easily separated after extraction simply by maintaining ethanol and methanol have high MW absorbing capacity.
the separator condition. Almost pure CO2 is collected and Water falls in the medium range capacity together with
can be recycled using a compressor. The solid, semi-solid acetic acid, butanol and dimethylformamide (DMF).
or liquid extracts are collected at the separator.
Polyphenols can be extracted in two ways. The sample
The supercritical carbon dioxide is vastly exploited for containing polar polyphenols, such as phenolic acids and
extraction of numerous phytochemicals including poly- flavonoids, are immersed in a microwave transparent
phenols, essential oils, etc. Tuning the condition, a range solvent. In this case, only the sample gets heated up.
of polyphenols can be extracted using supercritical Mass transfer occurs through the cell membrane to the
CO2. Several applications are summarized by del Valle solvent. Eventually the solvent temperature rises,
et al. [9] and Sookwong et al. [10]. Many industrial increasing the mass transfer rate. In addition, cell

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4 Food Engineering and Processing

structures encapsulating the polyphenols may be rup- 17.86 W/mL, and liquid/solid ratio 28:1). In this study,
tured at high enough temperatures, releasing the poly- yields were higher compared to ultrasound assisted
phenols into the solvent. In another method, solvents extraction (UAE) and conventional solvent extraction.
with high or medium absorbance capacity of MW, such as
methanol, ethanol, water or their mixtures, are used to Ultrasound assisted extraction (UAE)
extract polyphenols. Unlike microwave (electromagnetic wave), ultrasound
waves are sound waves with high frequency beyond
Extraction time, temperature, type of solvent, solvent human hearing capability. Considering healthy young
concentration, sample to solvent ratio and microwave adults, the upper limit of sound frequency for humans
power are the main factors to recover polyphenols using is 20 kHz. Hence, ultrasound devices for extraction work
MAE. A few advantages of MAE are the quick heating, in the range of 20 kHz to 2 MHz (less than the frequency
lower solvent requirements and clean process. The of MW). Sound waves have significant impact on an
extraction time is significantly reduced by controlling elastic medium such as liquid solvents, soft tissue of
the MW power. The method consumes less power due plant parts, etc. The medium changes in shape when
to the efficient heating process of microwave radiation. sound waves travel through and returns to its original
shape in the absence of sound waves. Therefore, high
Numerous applications of MAE to extract polyphenols frequency ultrasound waves act as a piston on the medium
from food materials and various parts of plants are found [27]. In the process, cavitation bubbles are generated
in the literature. The maceration and MAE techniques inside the medium; upon collapsing, millions of these
were compared in extraction of phenolic compounds from microscopic bubbles release energy, creating localized
olive leaves [18]. It was found that MAE had several high pressure and temperature zones. The mechanism
advantages over maceration in terms of yield and extrac- is known as the cavitation effect. This is applied in
tion time. Microwave assisted extraction technique recov- extraction of phytochemicals as depicted in Figure 1.
ered polyphenols and other phenolic compounds from
apple pomace [19], as well as from fresh and dried Centella The mechanism can be described in 4 steps [27]. In the
asiatica L. leaves [20]. Higher amounts of total phenolics first step, cavitation bubbles are generated near the
were extracted from four spices (Cinnamomum zeylanicum, surface of the plant matrix in the application of ultrasound
Coriandrum sativum, Cuminum cyminum, Crocus sativus) waves. In the second step, bubbles are collapsed, releas-
using MAE compared to ultrasound assisted extraction ing a microjet with pressure and temperature toward the
technique [21]. Different solvents, namely acetone, surface. In the third step, the matrix surface is ruptured
methanol, ethyl acetate and water, were used for extrac- and a direct contact is established between active ingre-
tions from various plant materials using MAE and the dients inside the cell and the outside solvent. Finally,
conventional reflux method [22]. The highest yields were active components are released and transported to the
obtained using water for the conventional method and solvent. In this way, ultrasound waves enhance the mass
60% acetone for MAE. In both methods, aqueous ethyl transfer. Because this mechanism works on any liquid
acetate had the lowest yields. medium, use of UAE is not restricted by the selection of
solvents, unlike MAE. It is a novel and unique way to
Many researchers have tried to optimize the extraction agitate a solid/solvent mixture where mechanical agita-
process using the response surface method. In this tech- tion is not possible or not safe due to corrosion. Generally,
nique, a mathematical equation of yield or recovery is an ultrasound generator probe is immersed in the solid/
developed as a function of influential parameters such as solvent mixture.
solvent concentration, microwave power, extraction time,
feed to solvent ratio, etc. Optimized parameters were UAE presents multiple advantages; it is a green efficient
found using response surface for recovering maximum way to increase mass transfer, it requires less solvent, and
amounts of phenolic compounds from licorice root (liquid it is compatible with any solvent (however, the solvents’
to solid ratio of 12.7/1, 80% ethanol and 5–6 minutes of affinity for the active components should be considered).
extraction) [23], and snake grass (solvent to feed ratio of All these factors reduce the cost of extraction using
14 ml/g and 50% ethanol) [24]. The Box–Behnken ultrasound. The applications of UAE are varied, including
designs of experiments were used to develop response extractions of essential oils to polyphenols. Influences of
surfaces for optimizing extraction of phenolic com- extraction time, temperature, solvent concentration, solid
pounds from Quercus bark [25]. Particle size of to liquid ratio, particle size, ultrasound power and fre-
0.5 cm  1 cm  0.3 cm, pH of 10.75 with 33% ethanol quency were investigated in several studies that extracted
or 0.38% of methanol were the optimum parameters [25]. polyphenols from kinnow peel [28], mango peel [29],
In another response surface model using Box–Behnken Clinacanthus nutans [30], hasemi rice bran [31], Doum
design of experiment, extraction parameters were opti- Hyphaene thebaica L. Mart. (Arecaceae) fruit [32], etc. A
mized from Pistacia lentiscus leaves [26] using MAE (46% combined method of ultrasound assisted and micro-
ethanol, extraction time 60 seconds, power density of wave assisted extractions was adopted for polyphenol

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Food polyphenols from vegetable materials Panja 5

Figure 1

Solvent

Matrix

Cavities

Surface
Current Opinion in Food Science

Mechanism of releasing active components from cells using ultrasound waves.

extraction in distilled water with optimum conditions of [40], and face centered cube [41] were utilized for opti-
solvent to material ratio of 55 ml/g, microwave power of mization of polyphenol extraction from spruce wood bark
90 W and 75 seconds of extraction cycle [30]. Another (70% ethanol and 60 minutes of extraction time at 54 C)
combined method included UAE followed by supercriti- [39], maize filaments (61.08% ethanol, solvent to material
cal CO2 to extract polyphenols from grape marc [33]. ratio of 26.83 ml/gm and ultrasonic power of 520.01 W)
[40], and Aronia melanocarpa by-products from a filter-tea
Researchers showed that UAE took much less time (just factory (50% ethanol, ultrasonic power of 206.64 W and
1 hour) than the traditional maceration technique 80.1 minutes of extraction time at 70 C) [41].
(72 hour) to extract polyphenols from Punica granatum
fruits at 30 C with 50% ethanol and 1:20 (g/mL) solid to
liquid ratio [34]. Similar results were found with citrus Enzyme assisted extraction (EAE)
peel, extracting several phenolic compounds simulta- Enzyme assisted extraction (EAE) is another new green
neously [35]. The influence of the type of solvent and technique where the addition of enzymes in the extrac-
extraction method on polyphenols from Orthosiphon sta- tion medium enhances the recovery. The main purpose of
mineus leaves were investigated [36]. In this study, UAE the enzyme in extraction from plant materials is to break
with 90 minutes extraction and maceration with 240 min- or soften the cell walls. This can give the active ingre-
utes extraction were compared using various solvents dients access to the solvent. Bound or dispersed phyto-
such as methanol, isopropyl alcohol, water, 50% metha- chemicals inside cells or on cell walls are difficult to
nol, 70% methanol, 50% isopropyl alcohol, and 70% extract using normal solvent extraction. Enzymes help
isopropyl alcohol. It was proven that aqueous alcohol to release those components in a unique way by digesting
(>40%) was more effective than pure solvent. The yield the surrounding materials.
of polyphenols was reduced for extraction times longer
than 90 minutes due to thermal degradation. Therefore, EAE is very effective for the extraction of
polyphenols that are bound with proteins or carbohy-
The response surface method is one of the common drates inside the cells or on the cell walls. Enzymes such
techniques to optimize the extraction process. Various as cellulose, pectinase, protease, etc. are commonly used.
optimum conditions were reported for extracting poly- The particle size and the ratio of enzyme and sample are
phenols or phenolic compounds from olive pomace (80% the key controlling factors to maximize the polyphenol
methanol, solvent to material ratio of 40 and 30 minutes of yield. The main step of the extraction method is enzy-
extraction time) [37], thymus serphyllum (30% ethanol, matic hydrolysis, where a mixture of sample, enzyme and
solvent to material ratio of 30 and particle size of 0.3 mm solvent (water in most cases) is incubated at low tem-
and 3 minutes of extraction time) [38]. peratures, around 35–50 C, with adjusted pH. The
enzyme works best in an acidic medium. The hydrolysis
To develop the response surface, various designs of is stopped by deactivating enzymes at an elevated tem-
experiments such as factorial [39], central composite perature of 80–90 C.

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The main advantage of EAE is that is an environmentally Unlike applications of electroporation in microbiology
friendly process. Water is widely used instead of organic where drugs are delivered from outside to the inside of
solvents or chemicals. The low temperature extraction cells, active ingredients inside cells are released to exter-
also prevents any degradation and the process requires nal solvent in PEF extraction. Depending on the inten-
less energy. The main drawback of EAE is its prolonged sity of the electric field, the damage to the membrane is
extraction time, which varies from 1 hour to 48 hours. either reversible, or it is permanent and hence irrevers-
Extractant is separated using filtration or centrifugation. ible. In the case of temporary damage, a live cell heals
itself after a short duration after withdrawing the electric
The significant parameters for the extraction of antioxi- field. The working principle of electroporation is shown
dant phenolics from black currant pomace were studied; in Figure 2.
these include: enzyme type (Grindamyl pectinase and
Macer8 FJ), time of hydrolysis (0–8 hour), hydrolysis Each type of cell has an electric endurance limit to protect
temperature (20–50  C), particle size (250–500 mm or the membrane, that is, cell membranes can withstand
500–1000 mm), substrate condition (with or without certain amount of electric field without any significant
seeds), and type of solvent (methanol or water) [42]. In damage. The minimum threshold value is the critical
another study, antioxidant phenolics were recovered at electric field (Ec) for the particular type of cells. Damage
40 C in an acetate buffer (pH 3.5) for 48 hour using to the cell membrane can occur when the electric field is
commercial enzymes such as Celluclast 1.5 L, Pectinex higher than the critical level, as shown in Figure 2. The
Ultra and Novoferm from grape wastes [43]. The maxi- severity of the damage depends on the intensity of the
mum amount was obtained at a temperature of 50 C using electric field. Damage is reversible (temporary) under low
the enzyme Celluzyme MX, with an enzyme to peel ratio to moderate intensity (not much higher than the critical
of 1.5% (w/w) [44]. Likewise, 35% more phenolics were value) field. On the other hand, the application of a high
recovered from raspberry solid wastes using enzymes intensity electric field causes irreversible (permanent)
Grindamyl and Maxoliva with 25% (V/V) aqueous ethanol damage to the membrane. Consequently, active ingredi-
in 18 hour of extraction at 50  C [45]. Enzyme-assisted ents inside the cell are exposed and extracted directly by
extraction with a ternary mixture of pectinolytic, cellulo- the solvent.
lytic and hemicellulolytic enzymes enhanced the recov-
ery of polyphenols from rose petals by 9–25% from [46]. Advantages of PEF include its non-thermal nature, selec-
Other applications of enzyme-assisted extraction include tive extraction, shorter extraction time, and clean process.
recovery of polyphenols from old tealeaves [47] and Non-thermal methods are particularly useful for ther-
pomegranate peel [48]. mally sensitive materials. Controlling the operating
parameters of PEF is simple. Operating parameters (i.
Pulsed electric field extraction (PEF) e. electric field strength, pulse duration and number of
Pulse electric field assisted extraction (PEF) is an emerg- pulses, the size of pores on the membrane) can be
ing non-thermal green technology for extraction of phy- manipulated in such a way that only the desired compo-
tochemicals from plant’s parts such as fruits, roots, leaves, nents can be released, keeping other components inside
etc. The temperature change of the solvent is very low the cell. Under optimum conditions, the recovery factor is
during the extraction. In this method, electric pulses of significantly increased with the minimum extraction time
moderate to high intensity are passed through samples [51].
placed between two electrodes. The method works based
on the principle of rupturing cell membranes subjected to Yields of polyphenols from apple mash were increased by
adequate external electric field. This technique is pri- applying an electric field strength of 450 V/cm for
marily used in microbiology to increase the permeability 10 milliseconds of specific energy less than 3 kJ/kg
of cell membranes to deliver chemicals, drugs or DNA [49]. The amount of polyphenols recovered from grape
inside the cell. The method to enhance permeability of skin were increased by PEF of 5 pulses per second with
cell membranes by applying external electrical force is 30 (at 24 C) to 60 kV (35 C) [52]. Researchers proved that
known as electropermeabilization or electroporation. PEF was necessary to extract some polyphenols from
grape pomace and peel, which were not possible to extract
Electric field strength (E = V/d), pulse duration and num- by other treatments [53]. Various factors such as pulse
ber of pulses are the important factors for efficient elec- duration (0.05 seconds), number of pulses (30), pause
troporation. According to Bazhal et al. [49], electric field between pulses (PBP, 0.5–3 seconds) and pulse strength
intensities in extraction from food materials are divided as (0.4–0.9 kV/cm) were examined to maximize recovery of
follows: low intensity (E  100–200 V/cm), moderate polyphenols from fresh tealeaves [54,55]. It was estab-
intensity (E = 300–1500 V/cm) and high intensity lished, based on this study, that the longer pulses were
(E > 1500 V/cm). In general, short pulses (micro or milli- more effective and maximum recovery was obtained with
seconds) of high electric intensity are the most effective 0.9 kV/cm for 0.5 seconds of PBP and 1.1 kV/cm for
way to extract phytochemicals in PEF. 3 seconds of PBP. PEF was applied to extract phenolics

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Food polyphenols from vegetable materials Panja 7

Figure 2

E < Ec

V
No Damage

d Active components E > Ec

Cell
Cathode

Anode

Solvent
Reversible Damage
Membrane E=V/d
E >> Ec

Irreversible Damage
Current Opinion in Food Science

The changes in cell membranes after applying external electric field.

Source: Modified from [50].

from apple pomace, sorghum flour (1, 2 and 3 kV/cm and Conclusion
500, 875 and 1250 microseconds), frozen/thawed Euro- New extraction methods for recovery of polyphenols are
pean blueberries (1, 2, 5 kV/cm and 1, 5, 10 kJ/kg) [56], emerging with the commitment to develop green tech-
and rapeseed stems and leaves (5 kV/cm) [57]. The nologies. The modern scientific advancements are guid-
response surface method coupled with Box–Behnken ing the development by providing technology such as
design of experiments was developed to determine opti- microwave oven, ultrasound probe, etc. Microwave
mum conditions for recovery of polyphenols from canola assisted, ultrasound assisted, pulsed electric field assisted
seed cake using microwave assisted extraction (5 minutes and enzyme assisted extractions are promising methods to
of extraction time, 633.3 W microwave power and liquid extract polyphenols from plant parts such as roots, leaves,
to solid ratio of 6) and pulse electric field extraction (30 V, fruits. Temperature, pressure, solvent to feed ratio, sam-
30 Hz, 10% ethanol in 10 seconds) [58]. Yield of phe- ple particle size, pH of solution, extraction time, micro-
nolic contents from olive paste was enhanced by 13.3% wave power (MAE), ultrasonic power, frequency (UAE),
after PEF treatment with 2 kV/cm electric field and electric field strength and pulse duration (PEF) are the
specific energy of 11.225 kJ/kg [59]. It was also proved main factors controlling the mass transfer and solubility of
that PEF had no negative impact in the quality of olive polyphenols. The impacts of these factors have been
oil. PEF was also applied in an industrial scale production evaluated by a series of experiments. To minimize the
facility with processing of 200 tons of red and white number of experiments, various design of experiments
grapes with electric field strength of 500 V/cm [60]. (DOE) methods such as central composite, Box–Behnken
Few issues, such as flux and temperature of the system and full factorial are applied. Use of response surface
in this industrial scale system, were found. method is one of the smart applications of mathematics to

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8 Food Engineering and Processing

determine optimum extraction conditions to maximize and extraction time. The optimum conditions of extraction were esti-
mated to be 62 C at 164 bar with 47 minutes of extraction time where
recovery. total phenolic content was 1423 mg/100 g.
13. Gadkari PV, Balarman M, Kadimi US: Polyphenols from fresh
Conflict of interest statement frozen tea leaves (Camellia assamica L.) by supercritical
carbon dioxide extraction with ethanol entrainer —
None declared. application of response surface methodology. J Food Sci
Technol 2015, 52:720-730.
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