New perspective in extraction of plant biologically active compounds by green solvents

Abstract

In many industrial processes, large quantities of volatile and flammable organic solvents are used in various reaction systems and separation steps define a major part of the environmental and economic performance of a process. Accordingly, a growing area of research in the development of green technologies is devoted to designing new, environmentally-friendly, and tunable solvents the use of which would meet both technological and economical demands. A brief overview of the up to date knowledge regarding most proposed green solvents, including supercritical and subcritical fluids (e.g. CO2 and water) and natural deep eutectic solvents is presented herein, with a special emphasis on green extraction of plant biologically active compounds.

Full text

Food
and
Bioproducts
Processing
1
0
9
(
2
0
1
8
)
52–73
Contents lists available at ScienceDirect
Food
and
Bioproducts
Processing
journal homepage: www.elsevier.com/locate/fbp
New
perspective
in
extraction
of
plant
biologically
active
compounds
by
green
solvents
Marina
Cvjetko
Bubaloa,
Senka
Vidovi´
cb,
Ivana
Radojˇ
ci´
c
Redovnikovi´
ca,∗,
Stela
Joki´
cc
aUniversity
of
Zagreb,
Faculty
of
Food
Technology
and
Biotechnology,
10000
Zagreb,
Croatia
bUniversity
of
Novi
Sad,
Faculty
of
Technology,
Bulevar
Cara
Lazara
1,
21000
Novi
Sad,
Serbia
cUniversity
of
Josip
Juraj
Strossmayer
in
Osijek,
Faculty
of
Food
Technology
Osijek,
Franje
Kuhaca
20,
31000
Osijek,
Croatia
a
r
t
i
c
l
e
i
n
f
o
Article
history:
Received
25
August
2017
Received
in
revised
form
19
February
2018
Accepted
2
March
2018
Available
online
10
March
2018
Keywords:
Natural
deep
eutectic
solvents
Green
extraction
Green
solvents
Subcritical
water
Supercritical
CO2
Plant
biologically
active
compounds
a
b
s
t
r
a
c
t
In
many
industrial
processes,
large
quantities
of
volatile
and
flammable
organic
solvents
are
used
in
various
reaction
systems
and
separation
steps
define
a
major
part
of
the
envi-
ronmental
and
economic
performance
of
a
process.
Accordingly,
a
growing
area
of
research
in
the
development
of
green
technologies
is
devoted
to
designing
new,
environmentally-
friendly,
and
tunable
solvents
the
use
of
which
would
meet
both
technological
and
economical
demands.
A
brief
overview
of
the
up
to
date
knowledge
regarding
most
proposed
green
solvents,
including
supercritical
and
subcritical
fluids
(e.g.
CO2and
water)
and
natural
deep
eutectic
solvents
is
presented
herein,
with
a
special
emphasis
on
green
extraction
of
plant
biologically
active
compounds.
©
2018
Institution
of
Chemical
Engineers.
Published
by
Elsevier
B.V.
All
rights
reserved.
Contents
1.
Introduction.
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2.
Supercritical
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subcritical
solvents
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54
2.1.
Supercritical
fluid
extraction
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55
2.2.
Subcritical
water
extraction
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56
3.
Natural
deep
eutectic
solvents
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61
4.
Future
trends
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68
Acknowledgment
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68
References
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68
1.
Introduction
Plants
represent
a
valuable
source
of
chemical
compounds
that
are
traditionally
used
as
the
main
source
of
components
or
ideas
in
the
∗Corresponding
author.
E-mail
address:
iradojci@pbf.hr
(I.
Radojˇ
ci´
c
Redovnikovi´
c).
development
of
new
drugs
(e.g.
steroids
and
alkaloids),
functional
foods
(e.g.
plant
sterols
and
stanols
as
cholesterol-lowering
ingredients
in
functional
foods),
and
food
additives
(e.g.
natural
flavor,
aroma
and
color)
(Azmir
et
al.,
2013).
These
compounds
are
referred
to
as
bioac-
tive
compounds
due
to
their
pharmacological
or
toxicological
effects
in
humans
and
animals.
The
typical
bioactive
compounds
in
plants
are
produced
as
secondary
metabolites,
generated
through
various
biological
pathways
in
secondary
metabolism
processes,
and
play
an
https://doi.org/10.1016/j.fbp.2018.03.001
0960-3085/©
2018
Institution
of
Chemical
Engineers.
Published
by
Elsevier
B.V.
All
rights
reserved.

Food
and
Bioproducts
Processing
1
0
9
(
2
0
1
8
)
52–73
53
Table
1
–
The
six
principles
of
green
extraction
(Chemat
et
al.,
2012).
Principle
Description
Innovation
by
selection
of
varieties
and
use
of
renewable
plant
resources
In
green
extraction,
fully
renewable
resources
have
to
be
favoured
either
with
intensive
cultivation
or
in
vitro
growth
of
plant
cells
or
organisms
Use
of
alternative
solvents
and
principally
water
or
agro-solvents
The
selection
of
a
suitable
solvent
is
based
on
workers’
safety,
process
safety,
environment
protection
and
the
sustainability
of
the
process,
meaning
that
green
solvent
should
be
chemically
and
physically
stable,
low
volatility,
easy
to
use
and
easy
to
recycle
with
the
possibility
of
reuse.
As
green
solvents
water,
supercritical
fluids
(CO2and
water),
solvents
based
on
organic
salts
(ionic
liquids
and
deep
eutectic
solvents),
and
agrosolvents
(e.g.
ethanol,
glycerol,
methyl
esters
of
fatty
acids
of
vegetable
oil,
terpenes)
are
considered.
Reduce
energy
consumption
by
energy
recovery
and
using
innovative
technologies
Massive
reduction
of
energy
consumption
through
optimising
existing
processes,
recovery
the
energy
liberated
during
the
extraction
process,
assisting
existing
processes
with
intensification,
and
a
full
process
innovation
(e.g.
recuperating
the
heat
liberated
during
vapour
condensation;
the
use
of
pulsed
electric
fields,
activation
by
microwaves
or
ultrasound).
Production
of
co-products
instead
of
waste
to
include
the
bio-
and
agro-
refining
industry
The
“Bio-refinery”
concept
can
be
considered
as
a
facility
that
combines
the
biomass
conversion
process
with
equipment
to
produce
high
value-added
compounds
from
agricultural
and
forest
residues
such
as
biofuels
and
biomaterials.
Reduce
unit
operations
and
favour
safe,
robust
and
controlled
processes
To
be
competitive
industries
involved
in
extraction
of
natural
products
(perfume,
cosmetic,
pharmaceutical,
food,
and
bio-fuel)
have
to
combine
process
intensification
with
cleaner
and
safer
extraction
protocols
(more
compact
production
units
and
a
reduced
number
of
unit
operations,
energy
and
raw
material
savings,
process
safety
control,
reduction
in
waste
and
ecological
footprint).
Aim
for
a
non-denatured
and
biodegradable
extract
without
contaminants
To
meet
the
requirements
of
the
market
and
of
the
regulations,
the
extract
must
meet
a
number
of
quality
criteria;
contrary
to
some
popular
misconceptions,
the
“natural”
state
of
the
extract
is
no
guarantee
of
its
harmlessness
to
man
and
the
environment.
The
extracts
must
be
obtained
from
precisely
identified
raw
materials;
must
have
precise
physico-chemical
properties
and
be
properly
stored;
the
extract
should
be
free
of
all
pollutants
such
as
pesticide
residues,
heavy
metals,
mycotoxins.
important
role
in
protecting
plants
from
biotic
or
abiotic
stress
(Dixon,
2001;
Azmir
et
al.,
2013).
According
to
biochemical
pathways
and
chemical
classes,
bioac-
tive
compounds
in
plants
can
be
categorised
in
several
main
chemical
groups:
glycosides
(cardiac
glycosides,
cyanogenic
glycosides,
glucosi-
nolates,
saponins
and
anthraquinone
glycosides),
phenolic
compounds
(phenolic
and
hydroxycinnamic
acids,
stilbenes,
flavonoids
and
anto-
cyanins),
tannins
(there
are
two
distinct
types
of
tannins;
condensed
tannins,
which
are
large
polymers
of
flavonoids,
and
hydrolysable
tan-
nins
which
are
polymers
composed
of
a
monosaccharide
core
with
several
catechin
derivatives
attached),
mono-
di-
and
sequi-terpenoids,
phenylpropanoids,
lignans,
resins,
alkaloids,
furocoumarines
and
naphthodianthrones,
proteins
and
peptides
(Bernhoft,
2010).
Typically,
extraction
and
isolation
of
bioactive
compounds
from
the
natural
sources
proceed
according
to
well-established
procedures:
(1)
exhaus-
tive
extraction
(maceration,
steam
or
hydro-distillation,
pressing,
decoction,
infusion,
percolation
and
Soxhlet
extraction);
(2)
additional
chemical
treatment
of
the
extracts
in
order
to
isolate
target
compounds
in
a
pure
form
(Chemat
et
al.,
2012).
Conventional
extraction
processes
are
quite
laborious,
time-consuming,
involve
large
amounts
of
solvents
such
as
hydrocarbons,
alcohols
and
chloroalkanes
since
majority
of
bioactive
compounds
are
not
soluble
in
water
and,
ultimately,
may
cause
some
target
molecule
degradation
and
the
partial
loss
of
volatiles
(Cravotto
et
al.,
2008).
Above
all,
in
spite
of
the
high
energy
consumption
and
the
large
amount
of
solvents,
the
yield
is
often
very
low
(Chemat
et
al.,
2012).
Therefore,
in
the
past
decade
safer
and
more
efficient
extraction
techniques
based
on
a
reasonable
compromise
between
eco-
nomic,
social
and
environmental
requirements,
have
been
considered.
The
concept
of
green
chemistry
was
first
used
in
1991
when
the
PT
Anastas
launched
a
specific
programme
of
implementation
of
sus-
tainable
development
in
chemical
technology
(US
EPA,
2012).
This
concept
was
based
on
12
principles
appearing
as
guidelines
used
to
design
chemical
products
and
processes
that
reduce
or
completely
remove
the
application
and
create
harmful
and
dangerous
substances
through
the
usage
of
chemicals
and
solvents
barely
detrimental
or
fully
unharmful
to
human
health
and
the
environment,
as
well
as
to
design
energy
efficient
and
safer
processes
and
facilitate
the
usage
of
renew-
able
feedstocks
if
possible
(Anastas
and
Eghbali,
2010).
Today,
green
chemistry
has
surpassed
the
field
of
chemistry
and
is
acknowledged
in
various
industrial
fields,
such
as
food
technology
and
biotechnol-
ogy.
Accordingly,
the
term
green
extraction
has
been
introduced
to
describe
extraction
techniques
for
by-products
valorisation
based
on
green
and
sustainable
technology
through
(i)
improvement
and
opti-
mization
of
exciting
processes;
(ii)
usage
of
non-dedicated
equipment,
and
(iii)
innovation
in
processes
and
procedures
including
discovery
of
alterative
solvents,
and
is
governed
through
six
principles
given
in
Table
1
(Chemat
et
al.,
2012).
The
major
part
of
the
green
techniques
is
summarized
in
principle
No.
2
which
accounts
for
the
design
of
new,
environmentally-friendly
and
tunable
solvents
which
would
meet
both
technological
and
eco-
nomic
demands,
which
is
also
one
of
the
priorities
of
EU
environmental
policy
and
legislation
for
the
period
2010–2050
as
well
as
the
reduc-
tion
of
hazardous
solvents
(Cvjetko
Bubalo
et
al.,
2015).
According
to
the
principles
of
green
chemistry,
the
selection
of
a
suitable
solvent
is
based
on
workers’
safety
(toxicity,
carcinogenicity,
mutagenicity,
absorption
through
the
skin
and
respiratory
system),
process
safety
(flammability,
explosiveness,
volatility,
creating
the
potential
perox-
ide),
environment
protection
(ecotoxicity,
persistence,
groundwater
contamination,
destruction
of
the
ozone
layer)
and
the
sustainabil-
ity
of
the
process
(the
ability
of
recycling
and
the
possibility
of
reuse)
(Alfonsi
et
al.,
2008),
meaning
that
green
solvent
should
be
chemically
and
physically
stable,
with
low
volatility,
easy
to
use
and
easy
to
recycle
with
the
possibility
of
reuse.
Therefore,
in
the
last
several
years
in
order
to
minimize
the
use
of
the
organic
solvents,
which,
due
to
their
toxic-
ity
have
undesirable
effects
on
the
environment
and
on
food
and
other
final
products’
quality
and
safety,
the
interest
for
green
extraction
tech-
nologies
has
been
greatly
increased.
For
that
reason,
modern
extraction
technologies
which
use
safe
and
non-toxic
solvents
(such
are
water,
carbon
dioxide,
and
ethanol)
have
been
introduced
and
applied
for
the
extraction
of
various
materials
and
compounds.
Some
of
these
tech-
nologies
are:
microwave
assisted
extraction
(MAE),
ultrasound
assisted
extraction
(UAE),
accelerated
solvent
extraction
(ASE)
and
pressurized
technologies,
such
are
supercritical
fluid
extraction
(SFE)
and
subcriti-
cal
water
extraction
(SWE),
also
called
superheated
water
extraction

54
Food
and
Bioproducts
Processing
1
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2
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1
8
)
52–73
Table
2
–
Advantages
and
disadvantages
of
extraction
processes.
Extraction
technique
Advantages
Drawbacks
SC-CO2extraction
•
Gentle
treatment
of
heat-sensitive
materials
(its
moderate
critical
temperature
of
31.2 ◦C
is
a
key
issue
for
the
preservation
of
bioactive
compounds
in
extracts)
•
Solvent
—
free
products
•
CO2as
solvent
does
not
cause
environmental
problems
and
is
physiologically
harmless,
germicidal
and
not
flammable.
•
CO2is
a
Generally
recognized
as
safe
(GRAS)
solvent
•
CO2is
inexpensive
solvent
•
Due
to
low
viscosity
and
relatively
high
diffusivity,
supercritical
CO2have
enhanced
transport
properties
than
liquids,
can
diffuse
easily
through
solid
materials
and
can
therefore
give
faster
extraction
rates.
•
Fragrances
and
aromas
remain
unchanged
•
Selective
extraction
and
fractionated
separation
•
Pure
extracts
by
means
of
few
process
steps
•
Changeable
solvating
power
(possibility
of
modifying
the
density
of
the
fluid
by
changing
its
pressure
and/or
temperature)
•
High
solubility
for
non/low
polar
substances
(for
example
volatile
compounds)
•
possibility
of
direct
coupling
with
analytical
chromatographic
techniques
such
as
gas
chromatography
(GC)
or
supercritical
fluid
chromatography
(SFC)
•
High
pressures
•
High
investment
cost
(requires
a
careful
business
plan
contemplating
the
cost/effective
analysis
of
the
desired
compounds
to
be
extracted)
•
Phase
equilibrium
of
the
solvent/solute
system
is
complex,
making
design
of
extraction
conditions
difficult
•
High
polar
substances
(sugars,
amino
acids,
inorganic
salts,
proteins,
.
.
.)
are
insoluble
•
The
use
of
high
pressures
leads
to
capital
costs
for
plant,
and
operating
costs
may
also
be
high
so
the
number
of
commercial
processes
utilizing
supercritical
fluid
extraction
is
relatively
small,
due
mainly
to
the
existence
of
more
economical
processes.
SWE
•
SWE
use
water
as
extraction
solvent,
which
is
safe,
non-toxic,
non-flammable
and
environment
friendly.
•
Obtained
extracts
are
safe,
without
trace
of
any
toxic
solvents.
•
SWE
is
characterized
by
higher
diffusion
into
the
plant
matrix
and
increased
mass-transfer
properties
in
comparison
to
other
extraction
techniques.
•
It
is
faster
extraction
technique
in
comparison
to
others.
•
SWE
can
be
applied
for
extraction
of
low-polar
as
well
as
non-polar
compounds.
•
Application
of
low
cost
and
easily
available
extraction
solvent
and
short
extraction
times
minimize
the
cost
of
extraction
process.
•
Uncomplicated
equipment.
•
The
high
investments
costs.
•
At
elevated
temperatures,
the
risk
of
unwanted
reactions
(caramelization,
Maillard
reactions)
is
increased
and
toxic
compounds
can
be
formed.
•
Increased
risk
of
tub
clogging
induced
by
reactions
of
caramelization.
•
At
elevated
temperatures
risk
of
hydrolysis
reactionis
increased
as
well
as
possible
degradation
of
temperature
sensitive
compounds
can
be
expected.
•
At
higher
temperature
extraction
could
be
less
selective
due
to
an
increase
of
solubility
of
other
matrix
compounds.
•
Due
to
severe
process
conditions
SWE
equipment
need
to
be
made
of
expencive
high
quality
materials
with
increases
general
corrosion
resistance
and
of
increased
strength
at
elevated
temperatures.
NADES
•
Simple
and
inexpensive
preparation
•
Sustainable
production
with
100%
atom
economy
production
and
theoretically
does
not
generate
waste
•
NADES
are
tailor-made
solvents
and
108combinations
are
estimated
•
It
is
possible
to
fine-tuned
physicochemical
characteristics
for
the
specific
purpose.
•
A
wide
polar
range,
with
high
degree
of
solubilisation
strength
for
different
compounds
•
Low
toxicity
and
biodegradable
•
Non-volatility
and
non-flammability
•
The
cost
of
NADES
is
comparable
to
conventional
solvent
•
The
high
viscosities
of
NADES
could
be
a
restrictive
(lower
extraction
efficiencies,
the
energy
required
for
stirring
and
pumping)
•
NADES
have
almost
zero
vapor
and
recovery
of
target
compound
could
be
difficult
•
Problems
with
NADES
recovery
and/or
recycling
•
Currently,
the
application
of
NADES
on
an
industrial
scale
is
possible
only
when
the
extract
is
directly
used
without
expensive
downstream
purification
steps.
or
pressurized
hot
water
extraction
(PHWE).
Apart
from
the
advan-
tage
which
refers
to
the
use
of
“green
and
safe”
extraction
solvent,
most
of
the
mentioned
extraction
technologies
are
much
more
effi-
cient
than
the
conventional
ones.
Selective
extraction
in
the
case
of
most
modern
extraction
technologies
is
enabled
by
the
simple
change
of
the
process
parameters
(temperature,
pressure,
flow,
power,
etc.),
which
make
them
appropriate
for
the
extraction
of
variety
of
differ-
ent
bioactive
compounds
without
the
change
of
the
applied
extraction
solvent.
Therefore,
according
to
Gil-Chávez
et
al.
(2013)
they
enable
the
production
of
highly
purified
products
which
make
them
avail-
able
for
an
extensive
range
of
applications.
Also,
solvents
based
on
organic
salts
(ionic
liquids
and
deep
eutectic
solvents),
and
agrosol-
vents
(e.g.
ethanol,
glycerol,
methyl
esters
of
fatty
acids
of
vegetable
oil,
terpenes)
are
considered
as
well.
However,
a
brief
overview
of
the
up
to
date
knowledge
regarding
most
proposing
green
solvents
includ-
ing
supercritical
and
subcritical
fluids
(e.g.
CO2and
water)
and
natural
deep
eutectic
solvents
is
presented
herein,
with
a
special
emphasis
on
green
extraction
of
plant
biologically
active
compounds.
Some
charac-
teristics
with
general
and
specific
advantages
and
disadvantages
of
the
proposed
methods
are
presented
in
Table
2.

Food
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55
2.
Supercritical
and
subcritical
solvents
2.1.
Supercritical
fluid
extraction
SFE
of
plant
biologically
active
compounds
is
a
topic
of
grow-
ing
interest.
In
our
previous
paper
(Joki´
c
et
al.,
2015)
we
gave
a
detailed
review
about
the
design
of
SFE
system.
SFE
allows
the
processing
of
plant
material
at
low
temperatures,
hence
limiting
thermal
degradation
and
also
avoids
harmful
toxic
solvents.
SFE
utilizes
supercritical
fluids,
which
above
their
critical
point,
exhibit
liquid-like
(solvent
power,
negligi-
ble
surface
tension),
as
well
as
gas-like
(elevated
diffusivity,
low
viscosity)
properties
(Capuzzo
et
al.,
2013).
More
than
90%
of
SFE
have
been
performed
with
carbon
dioxide
(CO2),
as
a
supercritical
solvent
because
it
possesses
low
critical
constants
(Tc
=
31.1 ◦C,
Pc
=
7.38
MPa)
and
inert
nature;
it
is
non-toxic,
non-explosive,
inexpensive,
readily
available
and
is
easy
removable
from
the
product.
CO2is
also
generally
recognized
as
a
safe
(GRAS)
solvent,
so
products
extracted
with
supercritical
CO2are
safe
with
respect
to
human
health
(Cvjetko
Bubalo
et
al.,
2015).
Supercritical
CO2is
a
very
nonpo-
lar
solvent,
has
a
polarity
comparable
to
liquid
pentane
and
is
compatible
for
the
extraction
of
weakly
polar
compounds
of
low
molecular
weight
such
as
carotenoids,
triglycerides,
fatty
acids,
aromas
etc.
(Herrero
et
al.,
2006).
The
general
rule
is
that
solubility
of
substances
in
supercritical
CO2decreases
with
the
increase
in
number
of
polar
functional
groups
(e.g.,
hydroxyl,
carboxyl,
amino,
and
nitro).
So,
supercritical
CO2polarity
index
makes
it
hardly
suitable
for
the
extraction
of
polar
sub-
stances
(for
example,
phenolic
compounds).
To
overcome
this
problem,
practical
approaches
involve
the
use
of
polar
co-
solvents
or
co-modifiers/entrainers.
Ethanol
and
methanol
are
mainly
used
as
co-solvents
to
change
the
polarity
of
the
supercritical
fluid
and
to
increase
its
solvating
power
with
respect
to
targeted
biologically
active
compounds
(Cvjetko
Bubalo
et
al.,
2015).
Water
can
also
be
added
as
a
modifier,
but
compared
to
methanol,
only
0.3%
(v/v)
of
water
can
be
completely
miscible
with
CO2and
because
of
that
fact,
water
cannot
sufficiently
improve
the
polarity
of
CO2as
much
as
methanol
can.
Modifiers
can
be
introduced
as
mixed
fluids
in
the
pumping
system
with
a
second
pump
and
a
mixing
chamber,
or
by
simply
injecting
the
modifier
as
a
liquid
into
sample
before
the
extraction.
The
second
way
is
less
suc-
cessful
because
it
leads
to
concentration
gradients
within
the
sample.
The
third
way,
very
rarely
applied,
is
the
usage
of
a
cylinder
tank
of
the
modified
CO2(Pourmortazavi
and
Hajimirsadeghi,
2007).
For
example,
if
we
look
at
grape
seeds
(material
that
has
been
explored
a
lot
in
the
last
few
years)
supercritical
CO2extraction
with/without
modifiers,
it
can
be
seen
that
the
modifier
has
a
main
influence
on
the
SFE
pro-
cess
of
grape
seeds.
Palma
et
al.
(1999)
showed
that
with
the
increase
of
the
polarity
of
CO2using
methanol,
it
is
possible
to
fractionate
the
extracted
compounds.
Using
pure
CO2in
the
extraction
of
grape
seeds,
authors
obtained
mainly
fatty
acids,
aliphatic
aldehydes
and
sterols,
while
the
addition
of
a
mod-
ifier
resulted
in
the
obtainment
of
the
phenolic
compounds
(mainly
catechin,
epicatechin
and
gallic
acid).
Every
fluid
can
be
used
as
a
supercritical
solvent.
How-
ever,
the
technical
viability
(critical
properties),
toxicity,
cost
and
solvation
power
determine
the
best-suited
solvent
for
a
particular
application.
Ethane,
propane
and
dimethyl
ether
have
been
used
as
supercritical
solvents
for
the
extraction
of
plant
biologically
active
compounds.
These
solvents
have
critical
points
that
are
comparable
with
CO2and
have
higher
polarity
index
than
CO2,
resulting
in
the
extraction
of
more
polar
compounds.
However,
experimental
results
show
that
supercritical
CO2offers
a
wider
range
for
the
fractionating
of
the
extracted
compounds
changing
operative
pressure
in
the
extractor
or
separators
(Pereira
et
al.,
2010).
Some
published
reports
proposed
nitrous-oxide,
N2O,
as
a
choice
of
the
extrac-
tion
fluid
for
the
analytical
SFE
(Alexandrou
et
al.,
1992;
Raynie,
1993).
Unfortunately,
this
fluid
has
been
shown
to
cause
vio-
lent
explosions
when
used
for
samples
having
high
organic
content
and
should,
therefore,
be
used
only
if
necessary.
Other
more
exotic
supercritical
fluids,
which
have
been
used
for
SFE,
were
sulfur
hexafluoride
(SF6)
and
freons,
especially
CHClF2
(Freon-22)
(Levy
et
al.,
1991).
In
some
research,
water
(H2O)
in
supercritical
state
was
also
used
as
a
solvent
despite
its
high
critical
temperature
and
pressure
(Tc
=
374 ◦C,
Pc
=
22.1
MPa).
Furthermore,
corrosive
nature
of
H2O
under
these
critical
conditions
has
limited
its
practical
applications
(Ong
et
al.,
2006).
Nevertheless,
water
as
pretreatment
of
plant
material
or
added
to
supercritical
CO2as
a
co-solvent
has
shown
the
influence
on
the
qualitative
and
quantitative
composition
of
the
extract
(Nguyen
et
al.,
1991;
Mehr
et
al.,
1996;
Joki´
c
et
al.,
2017;
Ivanovi´
c
et
al.,
2011).
Today,
SFE
is
not
only
used
in
laboratories,
namely,
it
is,
even
more
often,
also
used
on
a
large
scale
for
a
lot
of
industrial
applications.
The
most
developed
application
od
SFE
is
mainly
for
food
products
(decaffeination
of
coffee
and
tea),
food
ingre-
dients
(hops
and
aromas,
colorants,
vitamin-rich
extracts,
specific
lipids,
etc.),
nutraceuticals/phytopharmaceuticals
and
removal
of
pesticides
from
rice.
But
also
cleaning
purposes
were
tested
such
as
the
decontamination
of
soils
the
removal
of
residual
solvents
from
pharmaceutical
products,
the
extrac-
tion
of
flame
retardants
from
electronic
waste
or
precision
degreasing
and
cleaning
of
mechanical
and
electronic
parts.
The
first
industrial
plant
was
built
in
Germany
in
1978,
since
the
research
on
extraction
of
caffeine
from
coffee
beans
was
patented
in
1964
(Zosel,
1964).
Caffeine
is
soluble
in
pure
CO2,
but
for
the
decaffeination
process
of
coffee
and
tea
water
saturated
CO2has
to
be
used,
otherwise,
the
caffeine
is
imple-
mented
too
strong
in
the
matrix
of
the
raw
material
and
cannot
be
extracted.
From
the
beginning
of
‘70s
to
the
begin-
ning
of’
90s
nearly
50%
of
the
whole
production
capacity
for
the
decaffeination
of
coffee
and
tea
changed
to
SFE
pro-
cess.
Also
in
the
last
few
decades,
nearly
all
producers
of
hop
extracts
changed
to
SFE
process.
Further
applications
on
a
large
scale
are
related
to
the
extraction
of
nicotine
from
tobacco,
extraction
of
spices
(oleoresins),
medicinal
herbs
and
high
value
fats
and
oils.
These
plants
are
much
smaller
com-
pared
to
decaffeinated
plants
and
the
hop
plants
(Skala
et
al.,
2002).
Also,
SFE
is
used
for
the
removal
of
pesticides
from
material.
The
first
industrial
plant
for
the
extraction
of
pes-
ticides
from
cereals
was
built
in
Taiwan
in
the
end
of
1999.
SFE
had
a
wide
application
area
and
is
capable
of
extracting
a
wide
range
of
diverse
compounds
from
variety
of
raw
material
matrices
and
it
is
very
hard
to
present
it
in
one
paper.
So
we
collected
the
most
important
reviews
about
SFE
of
bioactive
compounds
which
are
presented
in
Table
3.
For
easier
understanding,
the
process
of
SFE
of
certain
natural
compounds
can
be
divided
into
two
categories:
(1)
undesired
substances
which
need
to
be
removed
from
plant
material,
(2)
biologically
active
compounds
that
are
desired
to
be
extracted
from
the
plant
material.
In
the
first
group,
the
most
common
applications
are:
decaffeination
of
cof-
fee
and
tea,
defatting
or
deoiling
of
press
cakes,
removal
of

56
Food
and
Bioproducts
Processing
1
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9
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2
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1
8
)
52–73
Table
3
–
The
selected
reviews
on
SFE
of
bioactive
compounds.
Targeted
group
Reference
Fatty
acids
Carotenoids
Phenolics
Terpenoids
Phytosterols
Tocopherols
Tocotrienols
Sanchez-Camargo
et
al.
(2017)
Phenolic
compounds
Fatty
acids
Carotenoids
Volatiles
Da
Silva
et
al.
(2016)
Resveratrol
Polyphenols
Barba
et
al.
(2016)
Fatty
acids
Essential
oil
Phenolic
compounds
Alkaloids
Herrero
et
al.
(2013)
Plant
flavors
and
fragrances
Capuzzo
et
al.
(2013)
Fats,
oils
Temelli
(2009)
Seed
oils
Polyunsaturated
fatty
acids
Carotenoids
Phospholipids
Catchpole
et
al.
(2009)
Essential
and
volatile
oils
Pourmortazavi
and
Hajimirsadeghi
(2007)
Vitamin
additives
De-alcoholised
wine/beer
Defatted
potato
chips
Encapsulate
liquids
Brunner
(2005)
Seed
oils
Essential
oils
Volatile
oils
Skala
et
al.
(2002)
Lipids/fatty
acids
Sahena
et
al.
(2009)
Fats,
oils,
lipids
King
(2002)
pesticides
from
cereals,
extraction
of
nicotine
from
tobacco,
reduction
of
the
alcohol
content
in
beverages
(de-alcoholised
beer
and
wine)
and
cholesterol
from
eggs.
Such
group
of
pro-
cesses
requires
a
high
selectivity
for
targeted
compounds
to
be
removed
in
order
to
maintain
flavour,
appearance,
smell
and
shape
of
the
treated
raw
material,
which
represent
the
main
product
(Skala
et
al.,
2002).
The
second
group
consists
of
biologically
active
compounds
that
we
want
to
extract
from
the
raw
materials:
biologically
active
compounds
of
medici-
nal
herbs
(antioxidants),
essential
oils
(volatile
compounds),
nutraceuticals
and
pharmaceuticals
(lycopene,
astaxanthin,
hyperforin
etc.),
seed
oils
(tocopherols
etc.),
oleoresins
from
spices,
and
natural
colours
(carotene,
chlorophyll)
etc.
Firstly,
for
the
extraction
of
the
desired
active
compound,
the
compound
must
be
soluble
in
supercritical
CO2at
a
mod-
erate
pressure
and
temperature.
The
solubility
can
vary
in
a
wide
range
by
changing
the
extraction
pressure
and
tempera-
ture.
Furthermore,
if
small
amount
of
a
modifier
(mentioned
in
the
text
above)
is
added
to
CO2,
it
increases
solubility,
as
well
as
improves
the
separation
characteristics
by
controlling
the
solubility
of
the
solvent.
So,
during
the
SFE,
it
is
very
important
to
understand
the
effects
of
the
different
parameters
on
the
yield
and
composition
of
the
obtained
extracts.
The
knowl-
edge
of
these
effects
is
not
only
useful
for
the
optimization
and
economic
evaluation
of
the
process,
but
also
for
the
abil-
ity
to
predict
the
SFE
process,
which
is
useful
for
scale-up,
as
well
as
for
the
design
and
the
optimization
of
an
indus-
trial
plant
(Reverchon
and
De
Marco,
2006;
Pourmortazavi
and
Hajimirsadeghi,
2007;
Mezzomo
et
al.,
2009;
Joki´
c
et
al.,
2012).
Different
factors,
such
as
particle
size,
porosity,
moisture,
nature
of
the
matrix,
as
well
as
process
parameters
such
as
pressure,
temperature,
solvent
flow
rate,
can
affect
the
SFE
results.
Raw
material
before
extraction
needs
to
be
ground
and
average
particle
size
of
the
milled
material
should
be
between
0.4–0.8
mm.
However,
if
the
particles
are
too
small,
although
better
for
mass
transfer,
they
decrease
the
fluidized
bed
veloc-
ity,
can
cause
clogging
of
filters
and
can
tend
to
channeling
inside
the
extraction
bed,
causing
a
loss
of
efficiency
and
yield
of
the
process.
So,
the
physical
structure
of
the
matrix
is
of
crit-
ical
importance,
as
the
extraction
efficiencly
is
related
to
the
ability
of
the
supercritical
CO2to
diffuse
within
the
matrix.
The
extraction
pressure
is
the
main
parameter
that
influ-
ences
the
extraction
efficiency.
As
a
general
rule,
the
solubility
of
the
desired
compound
increases
with
the
increase
of
the
extraction
pressure,
which
is
directly
a
result
of
the
increased
solvent
density.
Consequently,
the
higher
the
extraction
pres-
sure,
the
smaller
the
volume
of
fluid
necessary
for
a
given
extraction.
However,
high
pressure
is
not
always
recom-
mended
for
all
material
and
desired
compounds.
For
example,
it
is
a
general
rule
to
use
lower
pressures
(from
9
to
10
MPa)
and
mild
temperatures
(from
40
to
50 ◦C)
if
we
want
to
extract
essential
oil
from
aromatic
and
medicinal
herbs.
In
these
pro-
cess
conditions,
all
the
essential
oil
components
are
largely
soluble
in
supercritical
CO2.
Higher
pressures
result
in
higher
solubility,
but
also
in
the
complex
total
extract
and
difficult
analysis,
because
at
higher
pressures,
essential
oil
compo-
nents
are
extracted
together
with
cuticular
waxes.
Opposite
to
essential
oil,
seed
oils
need
to
be
extracted
at
higher
press-
sures
because
tryglycerids
forming
seed
oil
are
readily
soluble
in
supercritical
CO2at
temperature
of
40 ◦C
and
pressures
greater
than
28
MPa
(Reverchon
and
De
Marco,
2006).
The
effect
of
extraction
temperature
depends
on
the
applied
pressure
and
is
very
complex,
due
to
the
combina-
tion
of
two
variables,
density
and
vapour
pressure.
Briefly,
the
effect
of
temperature
on
the
extraction
rate,
at
constant
pressure,
is
due
to
two
mechanisms:
an
increase
in
the
pro-
cess
temperature
increases
the
solubility
due
to
solute
vapour
pressure
enhancement
and
reduces
the
solubility
due
to
the
decrease
in
the
solvent
density.
At
one
point
we
have
the
“crossover
effect”
where
the
solubility
of
solute
is
no
longer
dependent
on
the
density
of
supecritical
fluid
(King,
1997).
This
crossover
phenomena
is
generally
reported
for
SFE
of
seed
oils.
To
summarize,
temperature
affects
the
volatility
of
the
solute,
and
it
is
very
difficult
to
predict
its
influence
due
to
its
dependence
on
the
nature
of
raw
material.
For
a
non-volatile
solute,
a
higher
temperature
would
result
in
lower
extraction
recovery.
On
the
other
hand,
for
a
volatile
solute,
there
is
a
competition
between
its
solubility
in
CO2(which
decrease
as
the
temperature
increases)
and
it
volatility
(which
rises
with
increasing
temperature).
Also,
there
is
a
lot
of
research
where
temperature
of
the
supercritical
fluid
did
not
influence
the
extraction
efficiency.
In
Table
4
we
listed
some
of
the
most
commonly
used
applications
of
SFE
(plant
origin)
together
with
the
extraction
parameters
(temperature,
pressure,
co-
solvent).
2.2.
Subcritical
water
extraction
In
the
recent
years,
among
modern
extraction
technologies,
SWE
has
attracted
great
attention
due
to
its
unique
proper-
ties
and
a
wide
variety
of
possible
applications.
A
number
of
review
articles
have
identified
subcritical
water
as
an
effec-

Food
and
Bioproducts
Processing
1
0
9
(
2
0
1
8
)
52–73
57
Table
4
–
Supercritical
CO2extraction
of
plant
material
(selected
examples
of
plant
origin).
Material
Extract
Modifier
T
(◦C)
P
(bar)
Reference
Almond
Oil,
tocopherols
35–50
350–550
Leo
et
al.
(2005)
Angelica
root Oil
40
120
Doneanu
and
Anitescu
(1998)
Aniseed
Essential
oil
30
80–180
Rodrigues
et
al.
(2003)
Annatto
seed
Bixin
40–60
200–300
(Degnan
et
al.
(1991))
Aloe
vera
leaves
␣-Tocopherol
Methanol
32,41,50
350,400,450
Hu
et
al.
(2005)
Apricot
seed
Oil
Ethanol
40–70
300–600
Özkal
et
al.
(2005)
Basil
(leaves
and
flowers)
Total
extract,
linalool,
eugenol,
d-cadinene
40–60
100–300
Zekovi´
c
et
al.
(2014)
Black
pepper
Oleoresin,
piperine
35–55
200–300
Dang
and
Phan
(2014)
Borage
seed
Oil
40–60
200–300
Kotnik
et
al.
(2006)
Canola
seed
Oil
40–60
200–250
Pederssetti
et
al.
(2011)
Caraway
seed
Carvone,
limonene
32–75
75–300
Baysal
and
Starmans
(1999)
Carrots ␤-Carotene 57
250
Subra
et
al.
(1998)
Cashew
nut
shell Oil
60
200–300 Patel
et
al.
(2006)
Celery
Essential
oil
40
100
Miˇ
si´
c
et
al.
(2008)
Chamomile
␣-Bisabolol,
chamazulene,
matricine
30–40
100–250
Kotnik
et
al.
(2007)
Cherry
seed Oil
40–60 180–220 Bernardo-Gil
et
al.
(2001)
Chia
seed Oil
40–80 136–408
Uribe
et
al.
(2011)
Chilli
pepper Capsaicinoids
40–80
100–400
Perva-Uzunali´
c
et
al.
(2004)
Citrus
peel
Naringin
60
95
Giannuzzo
et
al.
(2003)
Cocoa
beans
Methylxanthines
(caffeine,theobromine)
Cocoa
butter
70
200–400
Mohamed
et
al.
(2002)
Cocoa
shell
Theobromine
50–85
150–450
Rossi
(1996)
Coffee
husk
Caffeine,
chlorogenic
acid
40–60
100–300
Andrade
et
al.
(2012)
Coriander
seed
Oil
35
200–300
Illésa
et
al.
(2000)
Corn
germ
Oil
35–86
210–525
Rebolleda
et
al.
(2012)
Cotton
seed
Oil
60–80
350–550
Bhattacharjee
et
al.
(2007)
Egg
yolk
Phospholipids
40
517
Boselli
and
Caboni
(2000)
Elderberry
pomace
Anthocyanins
Ethanol,
H2O
40
210
Seabra
et
al.
(2010)
Eucalyptus
Essential
oil
50
90
Della
Porta
et
al.
(1999)
Fennel
Essential
oil,
trans-anethole,
fenchone
40
81
Simándi
et
al.
(1999)
Flax
seed
Oil
50–70
300–500
Özkal
(2009)
Ginger
Oleoresin
Ethanol,
isopropanol
25–35
200–250
Zancan
et
al.
(2002)
Ginkgo
leaves
Terpenes,
flavonoids
60–110
242–312
Chiu
et
al.
(2002)
Grape
seed Phenolic
compounds Methanol
35
455
Palma
et
al.
(1999)
Grape
seed Oil
40,50,60
200,300,400
Joki´
c
et
al.
(2016)
Grape
skin
Resveratrol
Ethanol
40
150
Marti
et
al.
(2001)
Guarana
seed
Caffeine
Water
40–70
100–400
Salda ˜
na
et
al.
(2002)
Hemp
seed
Oil
40–60
300–400
Aladi´
c
et
al.
(2015)
Hiprose
Total
extract
35
250
Illés
et
al.
(1997)
Hop
Essential
oil
40
150,300
Zekovi´
c
et
al.
(2007)
Horsetail
Oleoresin
30,40
120–300
Michielin
et
al.
(2005)
Jojoba
seed
Oil
Hexane
70–90
200–600
Salgin
et
al.
(2004)
Lavender
Essential
oil,
monoterpenes,
coumarin,
herniarin
40–60
100–300
Jerkovi´
c
et
al.
(2017)
Lemongrass
Essential
oil
23–50
85–120
Carlson
et
al.
(2001)
Lovage
Essential
oil
40–50
80–350
Daukˇ
sas
et
al.
(1999)
Marjoram
leaves
Essential
oil
40–50
80–120
Reverchon
(1992)
Marigold
flowers
Total
extract
20–40
120–200
Campos
et
al.
(2005)
Mate
tea
leaves
Caffeine,
theophylline,
theobromine
40–70
138–255
Salda ˜
na
et
al.
(2000)
Melon
seed
Oil
40–80
200–400
Nyam
et
al.
(2011)
Neem
seed
Nimbin
35–60
100–260
Tonthubthimthong
et
al.
(2001)
Nutmeg
Oil
23
90
Spricigo
et
al.
(1999)
Olive
pomace
Oil
40–50
100–300
De
Lucas
et
al.,
2003
Orange
peel Essential
oil
40
100
Jerkovi´
c
et
al.
(2015)
Oregano
leaves
Flavonoids
Ethanol
40–60
150–350
Cavero
et
al.
(2006)
Palm
kernel
Oil
40–80
345–483
Zaidul
et
al.
(2007)
Paprika
Carotenoids,
tocopherol,
capsaicinoids
35–55
100–400
Daood
et
al.
(2002)
Parsley
seed
Oil
35–45
100–150
Louli
et
al.
(2004)
Passion
fruit
seed
Oil
40–60
150–250
Cardoso
De
Oliveira
et
al.
(2013)
Peach
seed
Oil
Ethanol
30–50
100–300
Mezzomo
et
al.
(2010)
Poppy
seed
Oil
50–70
210–550
Bozan
and
Temelli
(2003)

58
Food
and
Bioproducts
Processing
1
0
9
(
2
0
1
8
)
52–73
–
Table
4
(Continued)
Material
Extract
Modifier
T
(◦C)
P
(bar)
Reference
Pumpkin
seed
Oil
35–75
152–345
Mitra
et
al.
(2009)
Rape
seed
Oil
40–60
250–350
Yu
et
al.
(2012)
Rice
brain
␥-Oryzanol,
tocols
40–60
276–414
Yoon
et
al.
(2014)
Rosehip
seed Oil
40–80
150–450
Machmudah
et
al.
(2007)
Rosemary carnosic
acid,
carnosol 100
355
Tena
et
al.
(1997)
Safflower
seed
Oil
35–60
220–280
Han
et
al.
(2009)
Sage
Carnosolic
acid
Ethanol
100
250,350
Dauksas
et
al.
(2001)
Sea
buckthorn
Tocopherols,
lycopene,
␤-carotene
Methanol,
ethanol,
2-propanol
35–55
150–350
Kagliwal
et
al.
(2011)
Sesame
seeds
Oil
40–60
190–250
Corso
et
al.
(2010)
Soybean
seeds
Oil
40–60
300–500
Joki´
c
et
al.
(2012)
Savory
Total
extract,
carvacrol
40–60
100–350
Vladi´
c
et
al.
(2016)
Thyme Total
extract,
thymol,
carvacrol
40
80–400 Zekovi´
c
et
al.
(2000)
Tomato
skin
and
seed
Carotenoids,
tocopherols,
sitosterols
40–80
300–460
Vag i
et
al.
(2007)
Walnut
Oil
Ethanol
40–60
300–500
Salgin
and
Salgin
(2006)
Wheat
germ Total
extract,
phenolics,
tocopherols
40–60 148–602 Gelmez
et
al.
(2009)
Yarrow Essential
oil 40–60
100
Bocevska
and
Sovová
(2007)
Table
5
–
Properties
of
water
at
different
conditions
and
in
different
state
(Brunner,
2014).
Property Water
at
normal
conditions
Near-critical
water
Supercritical
water
T
(◦C)
25
350
400
P
(bar)
1
250
500

(kg
m−3)
997.45
625.45
577.79
ε
(–)
78.5
14.86
12.16
pKw
(–)
14.0
11.5
11.5
tive
solvent,
catalyst
and
reactant
for
hydrolytic
conversions
and
extractions
(Brunner,
2009).
SWE
is
an
environmentally
friendly
extraction
technology,
which
uses
water
as
an
extrac-
tion
solvent
at
temperatures
between
100 ◦C
and
374 ◦C,
and
at
high
enough
pressure
to
keep
the
water
in
the
liquid
state
(Ramos
et
al.,
2002).
At
the
temperature
above
374 ◦C
and
pres-
sure
above
220
bar,
water
is
considered
to
be
in
supercritical
state.
The
properties
of
water
at
normal
conditions,
subcriti-
cal/near
critical
state
and
supercritical
state
are
presented
in
Table
5.
As
can
be
seen
from
Table
5,
with
the
change
of
extrac-
tion
temperature
and
pressure
the
main
properties
of
water,
as
an
extraction
solvent,
are
changed.
SWE
attracted
great
attention,
especially
due
to
a
sig-
nificant
change
of
water
properties
caused
by
altered
temperature.
Namely,
at
ambient
conditions
water
is
con-
sidered
an
extremely
polar
solvent,
and
its
polarity
is
characterized
by
a
dielectric
constant
of
around
80.
In
this
state,
water
is
suitable
for
the
extraction
of
highly
polar
com-
pounds.
But,
at
the
temperature
between
100
and
374 ◦C,
and
under
high
enough
pressure
to
keep
the
water
in
the
liq-
uid
state,
the
polarity
of
water
considerably
decreases
and
it
becomes
suitable
for
the
extraction
of
both,
polar
and
non-
polar
compounds.
This
is
caused
by
a
dramatical
drop
of
the
dielectric
constant
with
increasing
temperature.
As
an
example,
in
the
subcritical
state,
the
water
dielectric
constant
decreases
to
about
33
at
200 ◦C
and
this
value
is
similar
to
some
organic
solvents,
such
as
methanol
(Herrero
et
al.,
2006;
Iba ˜
nez
et
al.,
2012;
Gil-Chávez
et
al.,
2013),
which
is
often
used
for
the
extraction
of
compounds
of
moderate
polarity.
According
to
Jo
et
al.,
at
the
temperature
of
250 ◦C,
the
dielec-
tric
constant
of
water
accounts
27,
while
with
the
further
increase
of
temperature
to
300 ◦C,
it
drops
to
20
(Jo
et
al.,
2013).
Therefore,
by
achieving
low
polarities
at
elevated
tempera-
tures,
the
SWE
technology
is
able
to
produce
high
extraction
yields
and
fast
extraction
times
for
a
number
of
hydrophobic
organic
compounds
(Herrero
et
al.,
2006).
At
elevated
tempera-
tures
in
a
subcritical
state,
surface
tension,
water
viscosity
and
density,
aside
from
polarity,
are
significantly
lowered
too.
At
elevated
temperatures
the
surface
tension
of
water
decreases;
this
enables
enhanced
water
wetting
of
the
extracting
mate-
rial
and
the
dissolution
of
targeted
compounds
in
the
solvent
much
faster.
Decreased
water
viscosity
is
enhancing
its
pen-
etration
inside
the
extracting
material
and
thus
improving
the
diffusion
rate.
The
improved
diffusion
rate
enables
accel-
erated
extraction
as
well.
The
density
of
water
at
saturated
pressure
goes
from
0.995
g
mL−1at
25 ◦C,
to
0.579
g
mL−1at
350 ◦C.
According
to
Plaza
and
Turner,
in
addition
to
the
men-
tioned
properties,
the
self-ionization
properties
of
water
also
vary
with
temperature.
Thus,
the
dissociation
constant
(Kw)
of
water
increases
with
two
units
from
1.0
×
10−14,
at
25 ◦C,
to
1.2
×
10−12,
at
350 ◦C,
with
the
maximum
value
of
4.9
×
10−12
at
250 ◦C.
This
implies
that
the
pH
changes
from
about
7.0
to
5.5
(Plaza
and
Turner,
2015).
These
unique
properties
of
subcritical
water,
as
well
as
the
fact
that
water
as
a
solvent
is
easily
available,
safe,
low
cost,
non-toxic,
non-flammable,
and
environmentally
friendly,
lead
to
a
number
of
studies
on
the
possibility
of
SWE
application
for
the
extraction/separation/isolation
of
various
compounds,
bioactive
and
many
others.
Until
now,
SWE
has
been
applied
for
the
extraction
of
antioxidants
(phenols
and
flavonoids),
essential
oils,
fatty
acids,
oils,
carotenoids,
sugars,
manni-
tol,
pectin,
resorcinol,
etc.
Aside
from
that,
the
application
of
SWE
for
the
isolation
of
PAHs
from
soils
has
been
stud-
ied
intensively.
Most
studies
on
SWE
are
investigations
on
the
extraction
of
antioxidants,
e.g.
phenolic
compounds,
from
a
wide
variety
of
sources
(herbs,
fruits,
seeds,
roots,
by-products,
waste
etc.)
(Table
6).
They
are
relatively
polar
compounds
and
compounds
of
different
stability,
and
this
should
be
taken
into
account
during
the
selection
of
the
adequate
extraction
tech-
nology
and
during
the
set-up
of
the
appropriate
extraction
conditions.
According
to
Plaza
and
Turner,
optimal
conditions

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59
Table
6
–
Application
of
SWE
for
phenolic
compounds
extraction.
Material
for
extraction/resource
Targeted
compound
SWE
operating
conditions
Reference
Mango
peels
Total
phenols
Investigated
range:
Temperature:
60–220 ◦C,
Extraction
time:
30–120
min
Solid
to
water
ratio:
1:10–1:50
pH
of
solution:
2–8
Optimal
conditions/highest
recovery:
180 ◦C,
90
min,
solid
to
water
ratio
1:40
and
pH
4
Tunchaiyaphum
et
al.
(2013)
Pomegranate
seed
residues
(Punica
granatum
L.)
Total
phenols
Investigated
range:
Temperature:
80–280 ◦C
Extraction
time:
15–120
min
Pressure:
60
bar
Solid
to
water
ratio:
1:10–1:50
Optimal
conditions/highest
recovery:
220 ◦C,
30
min,
solid
to
water
ratio
was
1:40
He
et
al.
(2012)
Uva
ursi
herbal
dust
Total
phenols
and
total
flavonoids
Investigated
range:
Temperature:
120–220 ◦C
Extraction
time:
10–30
min
Pressure:
30
bar
Added
acidifier,
HCl:
0–1.5%
Optimal
conditions/highest
recovery:
151.2 ◦C,
10
min,
1.5%
HCl
Naffati
et
al.
(2017)
Potato
peel
Total
phenols
Chlorogenic
acid,
Caffeic
acid,
Gallic
acid
Investigated
range:
Temperature:
100–240 ◦C
Extraction
time:
30–120
min
Pressure:
60
bar
Optimal
conditions/highest
recovery:
160–180 ◦C,
6
bar,
60
min
Singh
and
Salda ˜
na
(2011)
Cinnamon
bark
(Cinnamomum
zeylanicum)
Total
phenols Investigated
range:
Temperature:
150
and
200 ◦C
Extraction
time:10–60
min
Pressure:
60
bar
Optimal
conditions/highest
recovery:
200 ◦C,
60
min,
60
bar
Khuwijitjaru
et
al.
(2012)
Wild
garlic
(Allium
ursinum
L.)
Total
phenols
and
total
flavonoids
Investigated
range:
Temperature:
120–200 ◦C
Extraction
time:
10–30
min
Added
acidifier,
HCl:
0–1.5%
Optimal
conditions/highest
recovery:
180.92 ◦C,
10
min,
added
acidifier
1.09%.
To m ˇ
sik
et
al.
(2017)
Citrus
pomaces
Total
phenols
Investigated
range:
Temperature:
25–250 ◦C
Extraction
time:
60
min
Pressure:
10–50
bar
Optimal
conditions/highest
recovery:
200 ◦C,
14
bar,
60
min
Kim
et
al.
(2009)
White
grape
pomace
Total
phenols
Investigated
range:
Temperature:
170–210 ◦C
Extraction
time:
30
min
Pressure:
100
bar
Optimal
conditions/highest
recovery:
210 ◦C,
100
bar,
30
min
Pedras
et
al.
(2017)
Oregano
leaves
(Origanum
vulgare
L.)
Total
phenols
Investigated
range:
Temperature:
100–200 ◦C
Extraction
time:
15
and
30
min
Pressure:
103
bar
Optimal
conditions/highest
recovery:
150 ◦C,
30
min,
103
bar
Rodrıguez-Meizoso
et
al.
(2006)
Winter
savory
(Satureja
montana
L.)
Total
phenols
and
total
flavonoids
Investigated
range:
Temperature:
79.15–220.5 ◦C
Extraction
time:
5.9–34.1
min
Pressure:
30
bar
Optimal
conditions/highest
recovery:
220 ◦C,
20.8
min,
30
bar
Vladic
et
al.
(2017)
Spent
coffee
grounds
(Coffea
arabica
L.)
Total
phenols
Investigated
range:
Temperature:
110–190 ◦C
Extraction
time:
15–75
min
Pressure:
50
Optimal
conditions/highest
recovery:
177.00 ◦C,
55
min,
50
bar
Xu
et
al.
(2015)

60
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–
Table
6
(Continued)
Material
for
extraction/resource
Targeted
compound
SWE
operating
conditions
Reference
Ginger
(Zingiber
officinale)
Gingerol
Investigated
range:
Temperature:
130–140 ◦C
Extraction
time:
10–40
min
Pressure:
2
bar
Optimal
conditions/highest
recovery:
130 ◦C,
20
min,
2
bar
Yulianto
et
al.
(2017)
Black
tea
Myrcetine
and
Quercetin*
Kampherol**
Investigated
range:
Temperature:
110–200 ◦C
Extraction
time:
5–15
min
Pressure:
101
bar
Optimal
conditions/highest
recovery:
170 ◦C,
15
min,
101
bar*
200 ◦C,
15
min,
101
bar**
Cheigh
et
al.
(2015)
Celery
powder
Myrcetine
and
Quercetin*
Kampherol**
Investigated
range:
Temperature:
110–200 ◦C
Extraction
time:
5–15
min
Pressure:
101
bar
Optimal
conditions/highest
recovery:
170 ◦C,
15
min,
101
bar*
200 ◦C,
15
min,
101
bar**
Cheigh
et
al.
(2015)
Ginseng
leaf
Myrcetine
and
Quercetin*
Kampherol**
Investigated
range:
Temperature:
110–200 ◦C
Extraction
time:
5–15
min
Pressure:
101
bar
Optimal
conditions/highest
recovery:
170 ◦C,
10
min,
101
bar*
200 ◦C,
15
min,
101
bar**
Cheigh
et
al.
(2015)
Tumeric
rhizomes
(Curcuma
longa
L)
Curcumin
Investigated
range:
Temperature:
120–160 ◦C
Extraction
time:
6–22
min
Particle
size:
0.6–2
mm
Pressure:
10
bar
Optimal
conditions/highest
recovery:
140 ◦C,
10
bar,
14
min,
0.71
mm
Kiamahalleh
et
al.
(2016)
Onion
skin
Quercetin
Investigated
range:
Temperature:
100–190 ◦C
Extraction
time:
5–30
min
Mixture
ration
of
onion
skin
and
diatomaceus
earth:
0.5:3.5–2:2
Pressure
maintained
from
90
to
131
bar
Optimal
conditions/highest
recovery:
165 ◦C,
15
min,
mixture
ratio
of
1.5:2.5,
from
90to131
bar
Ko
et
al.
(2011)
*,**
Correspond
to
optimal
SWE
operating
conditions
given
in
next
column.
for
different
groups
of
phenolic
compounds
vary
greatly,
and
e.g.
for
flavonoids
which
are
extremely
labile
phenolic
com-
pounds,
whose
stability
depends
on
pH,
generally
require
lower
extraction
temperatures
in
SWE
(Plaza
and
Turner,
2015).
According
to
the
same
authors,
in
SWE,
phenolic
compounds
have
usually
been
extracted
up
to
temperatures
of
150 ◦C,
and
for
the
extraction
time
from
1
to
60
min
(Plaza
and
Turner,
2015).
But,
several
studies
have
revealed
that
in
the
case
of
cer-
tain
sources
and
certain
phenolics
even
higher
temperatures
and/or
longer
extraction
time
can
be
applied
(Pedras
et
al.,
2017;
Vladic
et
al.,
2017;
Tunchaiyaphum
et
al.,
2013;
He
et
al.,
2012;
Khuwijitjaru
et
al.,
2012;
Kim
et
al.,
2009).
Many
studies
revealed
the
higher
efficiency
of
phenolic
compounds
extraction
using
SWE
over
conventional
extrac-
tion
technologies.
In
the
study
by
Ko
et
al.,
the
efficiency
of
SWE
was
compared
with
conventional
extraction
tech-
nologies;
it
was
found
that
SWE
yielded
over
eight,
six-
and
fourfold
higher
concentration
of
quarcetin
in
comparison
to
extraction
technologies
using
ethanol,
methanol
and
water
at
the
atmospheric
boiling
point,
respectively
(Ko
et
al.,
2011).
Pedras
et
al.,
in
the
study
on
SWE
of
white
grape
pomace,
explained
the
higher
efficiency
of
SWE
in
comparison
to
con-
ventional
technologies
by
ephasizing
the
fact
that
phenolic
compounds
in
white
grape
pomace
are
entrapped
within
a
lignocellulose
structure,
and
their
release
requires
hydroly-
sis
of
the
lignocellulosic
structure.
On
the
other
hand,
lignin
is
rich
in
polyphenols,
and
its
partial
degradation
could
also
contribute
to
the
phenolic
content
(Pedras
et
al.,
2017).
Antho-
cyanins
extraction
from
fruit
berry
substrates,
investigated
by
King
et
al.,
showed
that
SWE
provided
an
equivalent
or
bet-
ter
results
than
those
obtained
using
conventional
ethanol
extraction
(King
et
al.,
2003).
According
to
Rangsriwong
et
al.
(2009)
phenolic
compounds
were
extracted
from
Terminute-
salia
chebula
Retz
fruits
also
by
application
of
SWE.
In
this
study
the
comparison
was
made
between
SWE
and
Soxhlet
extraction
methods.
The
result
revealed
that,
SWE
hydrolysis
required
only
37.5
min
to
recover
highly
substantial
amount
of
phenolic
compounds
while
soxhlet
extraction
method

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required
more
than
2
h
reaction
time
to
achieve
maximum
yield
of
phenolic
compounds.
In
the
study
by
Singh
and
Salda ˜
na,
where
recovery
of
eight
phenolic
compounds
(gallic
acid,
chlorogenic
acid,
caffeic
acid,
protocatechuic
acid,
syringic
acid,
p-hydroxyl
benzoic
acid,
ferulic
acid
and
coumaric
acid)
from
potato
peel
using
conventional
and
SWE
technology
was
investigated,
the
use
of
SWE
resulted
in
higher
amounts
of
phenolics
(81.83
mg
100
g−1)
than
the
amounts
obtained
with
methanol
extraction
(46.36
mg
100
g−1)
or
with
ethanol
extraction
(29.52
mg
100
g−1)
(Singh
and
Salda ˜
na,
2011).
The
efficiency
of
SWE
differs
from
conventional
extrac-
tion
technologies
not
only
by
the
total
phenolic
yield,
but
also
by
the
quality
and
number
of
extracted
individual
phe-
nolic
compounds.
Namely,
in
the
study
on
SWE
of
phenolic
compounds
from
cinnamon
bark,
Khuwijitjaru
et
al.
noticed
that
obtained
subcritical
water
extracts
contained
five
pheno-
lic
compounds
(caffeic,
ferulic,
p-cumaric,
protocatehuic
and
vanillic
acids),
while
only
three
compounds
were
identified
in
the
extract
obtained
by
conventional
organic
solvent
extrac-
tion
(Khuwijitjaru
et
al.,
2012).
The
study
by
Singh
and
Saldana,
on
the
recovery
of
eight
phenolic
compounds
from
potato
peel,
revealed
that
two
major
phenolic
compounds
(gallic,
28.56
mg
100
g−1,
and
caffeic,
12.22
mg
100
g−1)
from
potato
peel
were
more
efficiently
extracted
with
pure
methanol,
as
their
recov-
ery
with
ethanol
and
subcritical
water
was
lower
(8.62
and
5.18
mg
100
g−1,
and
9.23
and
14.59
mg
100
g−1,
respectively).
But,
the
recovery
of
gallic
acid
was
low
with
either
methanol
extraction
(0.46
mg
100
g−1)
or
ethanol
extraction
(0.60
mg
100
g−1),
while
SWE
yielded
significantly
higher
yield,
29.56
mg
100
g−1of
this
phenolic
acid
at
180 ◦C
(Singh
and
Salda ˜
na,
2011).
Aside
from
its
use
for
the
extraction
of
antioxidant
com-
pounds,
SWE
has
been
applied
for
the
isolation
of
essential
oils
from
various
plant
materials
(Table
7).
Generally,
in
SWE,
the
change
in
temperature
will
result
in
a
change
of
components
and
compositions
of
the
extracted
essential
oils.
According
to
several
studies
(Gámiz-Gracia
and
Luque
de
Castro,
2000;
Ozel
et
al.,
2003;
Khajenoori
et
al.,
2009),
in
SWE
with
the
increase
of
temperature,
if
the
target
compound
is
an
essen-
tial
oil,
the
increase
of
yield
can
be
expected
up
to
150 ◦C,
after
that
the
yield
decreases,
and
this
is
caused
by
the
degradation
of
the
essential
oil
components.
According
to
Gámiz-Gracia
and
Luquede
Castro,
from
150 ◦C
to
175 ◦C
the
yield
of
most
of
the
monoterpene
compounds
increased,
while
a
decrease
inoxygenated
compounds
has
been
noticed
(Gámiz-Gracia
and
Luque
de
Castro,
2000).
In
the
study
by
Khajenoori
et
al.,
on
the
extraction
of
essential
oil
from
Zataria
multiflora
Boiss
by
SWE,
it
has
been
noticed
that
the
efficiency
of
thymol
and
carvacrol
extraction
generally
increased
with
the
increase
in
temperature
up
to
15 ◦C,
at
175 ◦C
it
decreases
(Khajenoori
et
al.,
2009).
Miller
and
Hawethorne
reported
that
the
solu-
bility
of
d-limonene,
carvone,
eguenol,
1,8-cineole
and
nerol
increased
with
the
increase
in
temperature
up
to
200 ◦C
in
SWE
(Miller
and
Hawthorne,
2000).
SWE
has
several
advantages
over
hydrodistilation,
the
conventional
extraction
technology
usually
used
for
the
extraction
of
essential
oils.
Cleaner
features,
much
shorter
extraction
time
and
the
cost
of
extraction
are
among
its
main
advantages.
According
to
Soto
Ayala
and
Luque
de
Castro,
the
cost
of
extraction
is
clearly
advantageous
for
SWE.
Namely,
the
energy
cost
required
to
perform
hydrodistillation
is
ca.
20
times
higher
than
that
required
for
SWE.
This
feature
is
of
fundamental
importance
for
the
potential
future
implemen-
tation
of
this
technique
at
an
industrial
scale
(Soto
Ayala
and
Luque
de
Castro,
2001).
Further,
the
possibility
to
manipulate
the
composition
of
extracted
essential
oil
by
changing
the
pro-
cess
temperature
is
one
of
the
most
important
advantages
of
SWE.Aside
from
that,
according
to
several
studies
(Khajenoori
et
al.,
2013;
Eikani
et
al.,
2007),
SWE
enables
the
extraction
of
a
significantly
higher
amount
of
valuable
oxygenated
com-
ponents
in
comparison
to
conventional
methods,
Soxhlet
and
hydrodistilation,
and
this
has
an
impact
on
the
obtained
qual-
ity
of
extracts.
On
the
other
hand,
hydrodistillation
has
a
distinct
mechanism
of
extraction,
whereas
SWE
and
Soxhlet
extraction
mainly
consist
of
the
dissolution
and/or
solubili-
sation
of
the
essential
oil
in
solvent
(Khajenoori
et
al.,
2009).
Therefore,
a
positive
aspect
of
hydrodistillation
is
the
spon-
taneous
separation
of
the
two
immiscible
phases;
meanwhile
the
SWE
extract
is
an
emulsion
which
mustbe
broken
by
an
external
agent
(Soto
Ayala
and
Luque
de
Castro,
2001).
Aside
from
thestudies
on
the
extraction
of
antioxidant
compounds,
e.g.
phenols,
and
the
extraction
of
essential
oils,
the
appli-
cation
of
SWE
for
the
isolation/separation/recovery
of
many
other
compounds
from
different
plant
sources
has
been
inten-
sively
investigated
(Table
8).
3.
Natural
deep
eutectic
solvents
Deep
eutectic
solvents
(DES)
were
first
introduced
by
Abbott
et
al.
(2003),
who
reported
interesting
properties
of
eutec-
tic
mixtures
of
urea
and
a
range
of
quaternary
ammonium
salts.
Today,
DESs
are
widely
recognized
as
a
novel
class
of
sustainable
solvents
representing
a
green
alterative
to
ionic
liquids
(ILs).
Due
to
the
similar
properties
of
DESs
and
ILs
(non-
volatility,
non-flammability,
high
viscosity,
similar
starting
materials),
DESs
are
sometimes
referred
to
as
the
fourth-
generation
of
ILs,
even
though
they
are
not
entirely
composed
of
ionic
species.
DESs
are
prepared
simply
by
mixing
two
or
three
components
such
as
organic
salts
(quaternary
ammo-
nium
or
phosphonium
salt)
and
metal
salts
or
hydrogen
bond
donors
(HBD),
that
are
capable
of
associating
with
each
other
through
intramolecular
hydrogen
bonds.
The
charge
delocal-
ization
that
occurs
is
hereafter
responsible
for
the
decrease
in
the
melting
point
of
the
resulting
mixture,
relative
to
the
melt-
ing
points
of
the
starting
materials
(Paiva
et
al.,
2014).
However,
DESs
have
advantages
over
ILs,
such
as
lower
environmen-
tal
and
economic
impact.
This
is
especially
true
for
DESs
that
that
are
produced
from
primary
metabolites
common
in
liv-
ing
cells,
called
natural
deep
eutectic
solvents
(NADES),
that
are
generally
composed
of
components
that
are
abundant
in
our
daily
diet,
such
as
choline,
amines,
sugars,
polyalcohol
and
carboxylic
acids.
Actually,
NADESs
fully
fit
the
princi-
ples
of
green
chemistry
and
offer
many
advantages,
including
low
cost,
readily
available
component,
simple
preparation,
and
a
low
toxicity
profile.
Aside
from
that,
they
show
very
good
physicochemical
characteristics
(e.g.
negligible
volatility,
liquid
sate
even
at
temperatures
below
0◦C,
adjustable
viscos-
ity,
wide
polar
range,
high
degree
of
solubilisation
strength
for
different
compounds)
which
can
be
fine-tuned
for
spe-
cific
purposes
due
to
their
numerous
structural
possibilities
(Zhang
et
al.,
2012).
Moreover,
NADESs
probably
occur
in
liv-
ing
cells
and
are
involved
in
the
biosynthesis,
solubilisation
and
storage
of
various
poorly
water-soluble
metabolites
and
unstable
compounds
in
cells
(Choi
et
al.,
2011).
All
those
properties
provoke
a
number
of
ideas
for
the
application
of
NADESs
in
health
related
areas,
such
as
drug
delivery
systems,

62
Food
and
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Processing
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)
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Table
7
–
Application
of
SWE
for
essential
oil
extraction.
Material
for
extraction
SWE
operating
conditions
Reference
Fennel
(Foeniculum
vulgare)
Investigated
range:
Temperature:
50–200 ◦C
Pressure:
50
bar
Extraction
time:
5–50
min
Optimal
conditions/highest
recovery:
150 ◦C,
50
bar,
50
min
Gámiz-Gracia
and
Luque
de
Castro
(2000)
Wild
thyme
(Thymbra
spuicata)
Investigated
range:
Temperature:
100–175 ◦C
Pressure:
20–90
bar
Extraction
time:
30
min
Optimal
conditions/highest
recovery:
150 ◦C,
60
bar,
30
min
Ozel
et
al.
(2003)
Oregano
leaves
(Lippia
graveolens)Investigated
range:
Temperature:
100–175 ◦C
Pressure:
10–51
bar
Extraction
time:
30
min
Optimal
conditions/highest
recovery:
125 ◦C,
20
bar,
30
min
Soto
Ayala
and
Luque
de
Castro
(2001)
Chamomilla
(Matricaria
chamomilla
L.)
Investigated
range:
Temperature:
100–175 ◦C
Pressure:
20
bar
Extraction
time:
120
min
Optimal
conditions/highest
recovery:
150 ◦C,
20
bar,
120
min
Khajenoori
et
al.
(2013)
Coriander
(Coriandrum
sativum
L.)
Investigated
range:
Temperature:
100–175 ◦C
Pressure:
20
bar
Extraction
time:
20
min
Optimal
conditions/highest
recovery:
125 ◦C,
20
bar,
20
min
Eikani
et
al.
(2007)
Shirazi
thyme
(Zataria
multiflora
Boiss) Investigated
range:
Temperature:
125–175 ◦C
Pressure:
20
bar
Extraction
time:
60
min
Optimal
conditions/highest
recovery:
150 ◦C,
20
bar,
60
min
Khajenoori
et
al.
(2009)
Pepermint
(Mentha
piperita)
Investigated
range:
Temperature:
100–200 ◦C
Pressure:
60
bar
Extraction
time:
6–40
min
Optimal
conditions/highest
recovery:
150 ◦C,
30
min,
60
bar
175 ◦C,
12
min,
60
bar
Kubatova
et
al.
(2001)
bone-therapy
scaffolds,
and
other
food,
pharmaceutical
and
cosmetics
related
applications
(Faggian
et
al.,
2016;
Zainal-
Abidin
et
al.,
2017;
Li
and
Lee,
2016;
Mbous
et
al.,
2017).
There
is
also
an
increasing
number
of
studies
on
the
extraction
of
biologically
active
compounds,
including
flavonoids,
pheno-
lic
acid,
anthocyanin,
terpenoids,
alkaloids
and
saponins,
that
indicate
the
possible
utilization
of
NADESs
in
the
extraction
of
various
polar,
as
well
as
non-polar,
natural
compounds
(Zainal-Abidin
et
al.,
2017;
Ruesgas-Ramón
et
al.,
2017).
Among
the
biologically
active
compounds,
phenolic
compounds
are
studied
the
most
(Table
9).
In
order
to
design
efficient
extrac-
tion
methods
independently
of
target
compounds
by
using
NADESs,
the
following
steps
should
be
included:
(1)
selection
and
fine-tuning
of
physicochemical
characteristics
of
NADESs,
(2)
selection
and
optimization
of
the
extraction
method,
and
(3)
recovery
of
the
target
compounds
form
NADES,
if
it
is
nec-
essary.
NADESs’
capacity
to
extract
biologically
active
compounds
varies
considerably,
due
to
the
unique
physiochemical
prop-
erties
of
each
NADES.
In
order
to
select
the
ideal
NADES
for
certain,
Radoˇ
sevi´
c
et
al.
(2016)
values
polarity
and
pH
among
others.
The
first
step
is
the
selection
of
a
NADES
component
which
could
later
be
modified
by
changing
the
molar
ratio
between
the
components
and/or
by
the
addition
of
water.
Commonly,
it
is
necessary
to
try
several
typical
combina-
tions
which
considerably
differ
in
physiochemical
properties
in
order
to
select
a
suitable
NADES
(Dai
et
al.,
2013a;
Nam
et
al.,
2015;
Cvjetko
Bubalo
et
al.,
2016;
Wang
et
al.,
2016).
For
example,
Dai
et
al.
(2013b)
studied
the
extraction
of
aromatic
pigments
with
a
wide
range
of
polarity
from
Carthamus
tinc-
torius
L.
by
using
seven
NADESs,
indicating
that
the
NADES
with
the
lowest
polarity
showed
the
lowest
efficiency
for
polar
compounds
and
high
extractability
for
non-polar
com-
pounds.
This
corresponds
to
the
general
principle
of
“like
dissolves
like,”
i.e.,
that
polar
compounds
are
r
extracted
bet-
ter
by
using
a
polar
solvent,
and
vice
versa.
Similar
conclusion
was
also
obtained
for
the
extraction
from
grape
skin
phe-
nolic
compounds
(Jeong
et
al.,
2015a;
Cvjetko
Bubalo
et
al.,
2016;
Radoˇ
sevi´
c
et
al.,
2016).
Radoˇ
sevi´
c
et
al.
(2016)
applied
choline
chloride-based
NADESs
containing
organic
acid,
sugar
or
polyalcohol
as
HBD.
Organic
acid-based
NADESs
are
more
polar
that
sugar-
and
polyalcohol-based
ones,
with
polarity
close
to
that
of
methanol.
Moreover,
NADESs
with
organic
acids
are,
by
their
nature,
acidic,
whereas
sugars
or
polyal-
cohol
containing
NADESs
belong
in
the
group
of
solvents
with
pH
values
higher
than
6
(Dai
et
al.,
2014;
Radoˇ
sevi´
c
et
al.,

Food
and
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63
Table
8
–
Application
of
SWE
for
other
compounds
extraction.
Material
for
extraction/resource
Targeted
compound
SWE
operating
conditions
Reference
Oil
palm
Monosaccharide
Investigated
range:
Temperature:
170–200 ◦C
Pressure:
34–55
bar
Extraction
time:
5–15
min
Optimal
conditions/highest
recovery:
190 ◦C,
10
min,
41
bar
Norsyabilah
et
al.
(2013)
Ganoderma
lucidum
Polysaccharide
Investigated
range:
Temperature:
100–220 ◦C
Pressure:
40
bar
Optimal
conditions/highest
recovery:
170–220 ◦C,
40
bar
Matsunaga
et
al.
(2014)
Coconut
meal Oligosaccharide Investigated
range:
Temperature:
100–200 ◦C
Extraction
time:
30–240
min
Optimal
conditions/highest
recovery:
227 ◦C,
3
min
Khuwijitjaru
et
al.
(2012)
Sunflower
Oil
Investigated
range:
Temperature:
100–160 ◦C
Pressure:
bar
Extraction
time:
5–120
min
Solid:
liquid
ration:
1:10–1:30
Optimal
conditions/highest
recovery:
130 ◦C,
30
min,
30
bar,
solid
liquid
ration:1:20
Ravber
et
al.
(2015)
Citrus
peel
Pectin
Investigated
range:
Temperature:
100–140 ◦C
Extraction
time:
5
min
Optimal
conditions/highest
recovery:
120 ◦C,
5
min
Wang
et
al.
(2014)
Apple
pomace Pectin Investigated
range:
Temperature:
130–170 ◦C
Extraction
time:
5
min
Optimal
conditions/highest
recovery:
150 ◦C,
5
min
Wang
et
al.
(2014)
Sugar
beet
pulp
Pectin
Investigated
range:
Temperature:
110–130 ◦C
Pressure:
80–120
bar
Extraction
time:
20–40
min
Liquid
solid
ration:
30–50
Optimal
conditions/highest
recovery:
120.72 ◦C,
30.49
min,
107
bar,
solid–liquid
ration
44.03
Chen
et
al.
(2015)
Olive
leaves
Mannitol
Investigated
range:
Temperature:
100–150 ◦C
Pressure:
30–110
bar
Optimal
conditions/highest
recovery:
100 ◦C,
50
bar
Ghoreishi
and
Gholami
Shahrestani,
(2009)
Mahkota
Dewa
(Phaleria
macrocarpa)
Mangiferin
Investigated
range:
Temperature:
100–150 ◦C
Pressure:
7–40
bar
Extraction
time:
1–7
h
Optimal
conditions/highest
recovery:
100 ◦C,
5
h,
40
bar
Kim
et
al.
(2010)
2015).
Consequently,
organic
acid-based
NADESs
showed
the
best
extraction
results
for
anthocyanin,
while
sugar
based
NASEDs
were
a
better
choice
for
other
phenolic
compounds
(Radoˇ
sevi´
c
et
al.,
2016).
This
is
not
surprising
since
it
is
well
known
that
anthocyanins
are
highly
polar
compounds
and
that
an
acidic
environment
favours
their
extraction
and
sta-
bility
(Casta ˜
neda-Ovando
et
al.,
2009).
When
the
extraction
of
anthocyanin
from
Catharanthus
roseus
was
studied,
organic
acid
base-
and
polyalcohol-based
NADESs
showed
the
best
performance,
indicating
that
the
extraction
efficiency
is
likely
to
be
correlated
to
the
viscosity
of
NADESs
rather
than
to
their
polarity
and
pH
value
(Dai
et
al.,
2016).
However,
further
NADES
tailoring
by
changing
the
molar
ratio
of
the
selected
combination
is
possible
(Wei
et
al.,
2015;
Li
et
al.,
2015;
Qi
et
al.,
2015;
Wang
et
al.,
2016).
Wang
et
al.
(2016)
reported
that
the
extraction
yield
of
the
lipophilic
compound
tashinone
was
increased
when
the
choline
chloride/HBD
molar
ratio
declined
from
1:1
to
1:5,
while
a
further
decrease
of
the
ratio
to
1:6
showed
no
significant
changes.
Similarly,
a
NADES
with
choline
chloride
and
lactic
acid
was
selected
for
the
extraction
of
catehins
from
Camellia
sinensis
and
the
molar
ratios
from
1:1
to
1:4
were
tested
for
the
extraction
efficiency.
Extraction
yields
of
the
target
catechins
were
found
to
increase
with
the
change
of
choline
chloride/lactic
acid
from
1:1
to
1:2,
while
a
sustained
decrease
was
noticed
with
the
change
of
the
molar
ratio
from
1:2
to
1:4.
About
30%
lower
content
of
catechin
was
noticed
in
NADESs
with
the
molar
ratio
of
1:4,
compared
to
the
ratio
of
1:2.
This
could,
probably,
be
due
to
a
decrease
in

64
Food
and
Bioproducts
Processing
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(
2
0
1
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)
52–73
Table
9
–
Extraction
of
phenolic
from
natural
sources
using
NADES.
Tested
NADES
Method
of
extraction
Sources
Compunds
(the
most
promising
solvent)
References
GlyGln
Stirring
[OC:
600
rpm;
120
min;
70 ◦C;
CDES =
80%
(w/v);
RL/S =
32
mL
g−1]
Olea
europaea
leaves
Total
polyphenol
yield
(mg
GAE
g−1dw)
(GlyGln)
Athanasiadis
et
al.
(2017)
ChLa;
LaSa;
LaAa;
LaGlnW
UAE
[OC:140
W;
80 ◦C;
90
min;
CDES = 80%
(v/v)]
Native
Greek
medicinal
plants
–
dittany
(DI),
fennel
(FE),
marjoram
(MA),
mint
(MI),
sage
(SA)
Total
polyphenol
yield
(mg
GAE
g−1dw):
DI
(LaGlnW)
FE
(LaGlnW)
MA
(LaGlnW)
MI
(LaGlnW)
SA
(LaGlnW)
Total
flavonoid
yield
(mg
RtE
g−1dw):
DI
(LaGlnW)
FE
(LaAa)
MA
(LaAa)
MI
(ChLa)
SA
(LaGlnW)
Bakirtzi
et
al.
(2016)
ChCit;
ChOx;
ChMa;
ChGlc;
ChFru;
ChXyl;
ChGly
UAE
[OC:30.6
min,
341.5
W,
CDES =
64.6%
(v/v)]
Wine
lees
Total
anthocyanin
(ChMa)
Bosiljkov
et
al.
(2017)
ChSuc;
ChP;
ChGlc;
ChSol;
ProGlc;
LaGlc;
ChGlycol;
ChGly;
ChB1,3;
ChBut1,4;
ChHx1,6
MAEa[600
W,
RL/S =
14
mL
g−1,
11
min,
80 ◦C,
CDES =
70%]
UAE
HRE
Pigeon
pea
roots
Genistin
(ChHx1,6)
Genistein
(ChHx1,6)
Apigenin
(ChHx1,6)
Cui
et
al.
(2015)
ChGly;
ChOx;
ChMa;
ChSor;
ChProMa
Microwave-assisted
extraction
(MAE);
Ultrasound-assisted
extraction
methods
(UAE)a
[Optimal
condtions
(OC):
65 ◦C,
50
min,
CDES =
75%
(w/w),
35
kHz]
Grape
skin Quercetin-3-O-glucoside
(ChGly)
Malvidin-3-O-mono
glucoside
(ChOa)
Malvidin-3-O-acetylmonoglucosides
(ChOa)
Malvidin-3-(6-O-p-coumaroyl)
monoglucosides
(ChOar)
Peonidin-3-(6-O-p-coumaroyl)monoglucosides
(ChOa)
Petunidin-3-O-monoglucoside(ChOa)
Peonidin-3-O-monoglucoside(ChOa)
Cyanidin-3-O-monoglucoside
(ChProMa)
Delphinidin-3-O-monglucoside
(ChProMa)
(+)-Catechin
(ChOa)
Cvjetko
Bubalo
et
al.
(2016)
ChP;
LaGlc;
ProMa;
ChMa;
ChGlc;
FruGlcSuc
Mechanical
stirringa[OC:
40 ◦C,
30
min];
Ultrasound-assisted
extraction
with
heating
(UEH)
Catharanthus
roseus
Hirsutidin
3-O-(6-O-p-coumaroyl)
glucose
(ChP/LaGlc)
Petunidin
3-O-(6-O-p-coumaroyl)
glucose
(ChP/LaGlc)
Malvidin
3-O-(6-O-p-coumaroyl)
glucose
(ChP/LaGlc)
7-O-methylcyanidin
(ChP/LaGlc)
7,3-O-dimethylcyanidin
(ChP/LaGlc)
(Dai
et
al.
2016)

Food
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65
–
Table
9
(Continued)
Tested
NADES
Method
of
extraction
Sources
Compunds
(the
most
promising
solvent)
References
LaGlc;
CitGlc;
CitFru
UAEa[OC:0–60
min;
40 ◦C;
LaGlc,
5:1,
CDES =
85%;
200
W]
Onion,
olive,
tomato
and
pear
industrial
by-
products
Gallic
acid
(LaGlc)
3-Hydroxytyrosol
(LaGlc)
Tyrosol
(LaGlc)
Catechin
(LaGlc)
Caffeic
acid
(LaGlc)
Rutin
(LaGlc)
Coumaric
acid
(LaGlc)
Trans-Ferulic
acid
(LaGlc)
Ooleuropein
(LaGlc)
Cinnamic
acid
(LaGlc)
Quercetin
(LaGlc)
Luteolin
(LaGlc)
Naringenin
(LaGlc)
Apigenin
(LaGlc)
Fernández
et
al.
(2018)
ChP;
ChGly;
ChGlc;
ChSuc
ChXylol;
ChSol;
ProGly;
GlyGln;
GlyAla;
GlyHis;
GlyThr;
GlyLys;
GlyArg
UAE
[20
kHz,
200
W
CDES =
80%,
w/w]
Tartary
buckwheat
hull
Rutin
(ChGly)
Huang
et
al.
(2017)
ChMa;
ChCit;
ChGly;
ChGlc;
ChFru;
ChGal;
ChRib;
ChSuc;
ChCalt;
ChCal;
CitMalt;
CitMal
UAEa[OC:9.23
min,
CDES =
76.20%
w/w,
RL/S =
7.3
mL
g−1]
Stirring;
heating;
vortexing;
stirring
−
heating
Grape
skin
Total
anthocyanins
(cyanidin-3,5-diglucoside
equivalents;
mg)
(CitMalt)
Jeong
et
al.
(2015a)
CitAdo;
CitGlc;
CitGal;
CitPro;
CitB;
ChMa;
Ch:Cit;ChCl:Xylol;
ChAdo;ChGlc;ChFru;
ChGly;
GlyXylol;
GlyPro;
GlyB;
GlyMa;
GlyFru;
GlySuc;
ProSuc;
BSuc;
ChSuc;
GlyProSuc;
GlyBSuc;
GlyChSuc
Stirring;
heating;
heating
+
stirring;
UAEa
[21.5
min;
CDES =
66.1%
w/w;
RL/S =
19
mL
g−1]
White
ginseng
Ginsenosides
(mg
of
five
ginsenosides
g−1dw)
(GlyProSuc)
Jeong
et
al.
(2015b)
BSuc;
BSol;
BMalt;
BGlc;
BMal;
BXylol;
BU;
BGly;
BCit;
CitSuc;
CitSol;
CitMalt;
CitMal;
CitGlc;
CitXylol;
CitFru;
CitGly;
GlySuc;
GlySol;
GlyMalt;
GlyMal;
GlyGlc;
GlyXylol;
GlyFru;
GlyGal;
GlyU;
BGlyMalt;
BGlyMal;
BGlyU;
BGlyCit;
BGlyGlc;
CitGlyMalt;
CitGlcMal;
CitGlyGlc;
UGlyMalt;
UGlyMal;
UGlyGlc;
BGlyGlc
Stirring;
heating;
heating
+
stirring;
UAEa
[6.5
min;
CDES =
81%
w/w;
RL/S =
18
mL
g−1]
Camellia
sinensis
Catechin
(epicatechin,
epigallocatechin,
epicatechin-3-gallate,
epigallocatechin-3-gallate;
mg
g−1dw)
(BGlyGlc)
Jeong
et
al.
(2017)

66
Food
and
Bioproducts
Processing
1
0
9
(
2
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1
8
)
52–73
–
Table
9
(Continued)
Tested
NADES Method
of
extraction Sources Compunds
(the
most
promising
solvent) References
ChGly;
GlySa;
GlySatW UAEa[OC:80◦C,
90
min,
140
W,
37
kHz,
35
W
L−1]
Red
grape
pomace
(RGP),
Olive
leaves
(OLL),
Wheat
bran
(WB),
Spent
filter
coffee
(SFC),
Onion
solid
wastes
(OSW),
Lemon
waste
peels
(LMP)
Total
polyphenol
yield
(mg
GAE
g−1dw):
LMP
(ChGly)
OLL
(ChGly)
OSW
(GlySatW)
RGP
(ChGly)
SFC
(ChGly)
WB(ChGly)
Total
flavonoid
yield
(mg
RtE
g−1dw):
LMP
(ChGly)
OLL
(GlySa)
OSW
(ChGly)
RGP
(ChGly)
SFC
(GlySa)
WB
(ChGly)
Mouratoglou
et
al.
(2016)
ChGly;
ChXylol;
ChGlc;
ProGlc;
CitGlc;
CitAdo;
BMa;
ProGly;
ProXylol
UAEa[OC:45
min ◦C,
CDES =
90%
w/w;
330–450
W];
Heat
reflux
extraction
(HRE)
Flos
sophorae
Quercetin
(ProGly)
Kaempferol
(ProGly)
Isorhamnetin
glycosides
(ProGly)
Nam
et
al.
(2015)
ChGly;
ChB1,4;
ChB1,3;
BHgly;
BHb1,4;
BHb1,3;
ChEg;
BHeg;
ChBHeg
negative
pressure
cavitation-assisted
extraction
(NPCE)a
[−0.07
MPa,
60 ◦C,
RL/S =
25
mL
g−1,
20
min,
CDES =
80%
(v/v)];
UAE
Equisetum
palustre
L.
Kaempferol-
3-O-ˇ-d-glucopyranoside-7-O-ˇ-d-Glucopyranoside
(ChBHeg)
Kaempferol-3-O-ˇ-d-rutinoside-7-O-ˇ-d-glucopyranoside
(ChBHeg)
Luteolin-7-O-ˇ-d-glucopyranoside
(ChBHeg)
Quercetin-3-O-ˇ-d-glucopyranoside
(ChBHeg)
Apigenin-5-O-␤-d-glucopyranoside
(ChBHeg)
Genkwanin-5-O-␤-d-glucopyranoside
(ChBHeg)
Luteolin
(ChBHeg)
Apigenin
(ChBHeg)
Genkwanin
(ChBHeg)
Qi
et
al.
(2015)
ChGly;
ChGlc;
ChGal;
ChPro;
ChMa;ChXylol;
ChFru;
ChSuc;ChCit;
GlyXylolFru
MAEa[OC:
64.46 ◦C;
RL/S =
17.53
mL
g−1,
GlyXylolFru
3:3:3CDES =
80%
(v/v);
24.34
min]
UAE
Ficus
carica
L.
leaves
Caffeoylmalic
acid
(GlyXylolFru)
Psoralic
acid-glucoside
(GlyXylolFru)
Rutin
(GlyXylolFru)
Psoralen
(GlyXylolFru)
Bergapten
(GlyXylolFru)
Wang
et
al.
(2016)
ChB1,4;
ChGly;
ChEg;
ChCit;
ChMa;
ChLa;
ChGlc;
ChSol;
ChSuc;
ChMalt;
CitSuc;
CitGlc;
LaSuc
MAE
[OC:
60 ◦C;
12
min;
RL/S =
15
mL
g−1CDES =
80%
(v/v)
Radix
Scutellariae Baicalin
(ChLa)
Wogonoside
(ChLa)
Baicalein
(ChLa)
Wogonin
(ChLa)
Wei
et
al.
(2015)
OC
—
optimal
conditions.
CDES —
concentration
of
natural
deep
eutectic
solvents.
RL/S —
liquid/solid
ratio.
Component
abbreviations:
Aa,
ammonium
acetate;
Ala,
alanine;
Ado,
adonitol;
Arg,
arginine;
B,
betaine;
B1,3,
1,3-butanediol;
B1,4,
1,4-butanediol;
Cal,
caltose;
Calt,
caltitol;
Ch,
choline
chloride;
Cit,
citric
acid;
Eg,
ethylene
glycol;
Fru,
fructose;
Gal,
galactose;
Glc,
glucose;
Gln,
glycine;
Gly,
glycerol;
Glycol,
glycol;
H1,6,
1,6-hexanediol;
Hb1,3,
hydrochloride-1,3-butanediol;
Hb1,4,
hydrochloride-1,4-butanediol;
Heg,
hydrochloride-
ethylene
glycol;
Hgly,
hydrochloride-glycerol;
His,
histidine;
La,
lactic
acid;
Lys,
lysine;
Ma,
malic
acid;
Mal,
maltitol;
Malt,
maltose;
Ox,
oxalic
acid;
P,
1,2-propanediol;
Pro,
proline;
Rib,
ribose;
Sa,sodium
acetate;
Sat,
sodium–potassium
tartrate;
Sol,
sorbitol;
Sor,
sorbose;
Suc,
sucrose;
Thr,
threonine;
U,
urea;
W,
water;
Xyl,
xylose;
Xylol,
xylitol.
aThe
best
extraction
method.

Food
and
Bioproducts
Processing
1
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(
2
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1
8
)
52–73
67
the
amount
of
choline
chloride,
which
led
to
the
reduction
of
the
proportion
of
hydrogen
bond
receptors
in
the
NADES
system,
negatively
influencing
the
major
mechanism
of
solu-
bility
of
bioactive
compounds
(Li
et
al.,
2015;
Wei
et
al.,
2015).
Namely,
NADESs
have
the
ability
of
donating
and
accepting
protons
and
electrons,
which
confers
them
the
ability
to
form
hydrogen
bonds,
thus
increasing
their
dissolution
capability
(Dai
et
al.,
2013a,b;
Nam
et
al.,
2015).
A
further
improvement
of
the
extraction
efficiency
could
be
obtained
by
the
optimization
of
NADESs
water
content
(Zainal-Abidin
et
al.,
2017;
Ruesgas-Ramón
et
al.,
2017).
The
addition
of
water
leads
to
a
decrease
in
the
viscosity
of
NADESs,
thus
enhancing
the
mass
transfer
from
plant
matri-
ces
to
a
solution,
and
increasing
the
extraction
efficiency.
The
viscosity
of
NADESs
is
generally
very
high
at
room
tempera-
ture,
which
is
one
of
the
major
problems
when
using
NADESs
as
extraction
solvents
(Zhang
et
al.,
2012).
For
example,
some
NADESs
cannot
even
be
used
for
extraction
without
the
addi-
tion
of
water,
due
to
problems
NADESs
have
with
transferring
and
filtering
(Cvjetko
Bubalo
et
al.,
2016).
On
the
other
hand,
the
addition
of
water
causes
a
decrease
in
hydrogen
bonding
interactions
between
the
NADESs
and
the
target
components.
Moreover,
a
large
excess
of
water
in
the
NADESs
could
break
the
halide-HBD
supramolecular
complex
and
a
simple
aque-
ous
solution
of
the
individual
components
could
be
obtained
(Dai
et
al.,
2016).
Aside
from
that,
the
water
content
influ-
ences
the
polarity
of
the
NADES,
thus,
the
addition
of
water
should
be
optimised
for
each
NADES
and
target
compound.
In
general,
NADESs
with
high
water
content
are
better
for
polar
compounds
and
NADESs
with
low
water
content
are
more
suitable
for
the
extraction
of
less
polar
compounds
(Dai
et
al.,
2013b).
However,
in
many
cases
the
addition
of
water
between
20–30%
(w/w)
has
a
beneficial
influence
on
the
extraction
yield
of
both
polar
and
non-polar
compounds
(Wei
et
al.,
2015;
Li
et
al.,
2015;
Cvjetko
Bubalo
et
al.,
2016;
Huang
et
al.,
2017).
Fur-
thermore,
the
stability
of
target
compounds
in
NADESs
should
be
considered
as
an
important
factor
for
NADES
selection
(Dai
et
al.,
2014,
2016).
Dai
et
al.
(2014)
studied
the
stabil-
ity
of
phenolic
compounds
in
safflower
extracts,
indicating
that
the
stabilization
of
phenolic
compounds
in
some
typi-
cal
NADESs
was
better
than
in
conventional
solvents
such
as
ethanol
and
water.
The
stabilisation
ability
of
NADESs
cor-
related
with
strong
hydrogen
bonding
between
solutes
and
solvent
molecules,
while
among
the
tested
NADESs,
sugar-
based
ones
showed
the
best
results
(Dai
et
al.,
2014).
This
interaction
decreases
the
movement
of
solute
molecules,
reducing
their
contact
time
with
oxygen
and
the
interface
of
NADESs
and
air,
and
consequently
reducing
oxidative
degra-
dation,
which
is
the
major
degradation
mechanism
(Dai
et
al.,
2016).
Data
on
bioactive
compounds
stability
in
NADESs
are
scarce
and
extra
work
is
necessary
in
order
to
provide
further
understanding
of
the
stabilizing
ability
of
NADESs.
In
addition,
prior
to
the
final
selection
of
the
NADES,
the
evaluation
of
its
environmental
impact
should
be
performed
(Radoˇ
sevi´
c
et
al.,
2015;
Hayyan
et
al.
2016;
Radoˇ
sevi´
c
et
al.,
2016).
The
assumption
that
NADESs
are
benign
is
based
on
the
toxicity
data
for
the
components
that
make
up
the
NADESs,
which
are
biomaterial-derived
and
pharmaceutically
accept-
able.
This
theory
does
not
take
into
account
the
possibility
of
a
synergetic
effect
of
combining
the
compounds
in
the
NADES,
which
could
have
a
significant
impact
on
the
biolog-
ical
properties
of
such
mixtures
(Paiva
et
al.,
2014;
Radoˇ
sevi´
c
et
al.,
2015;
Hayyan
et
al.,
2016).
Also,
many
authors
suggest
that
the
NADESs
containing
organic
acids
as
the
HBD
(for
instance
oxalic,
citric,
malic,
or
tartaric
acids)
exhibit
greater
cytotoxicity
in
vitro
than
the
NADESs
containing
sugars
as
the
HBD
(for
instance
glucose,
mannose,
fructose,
and
xylose)
(Radoˇ
sevi´
c
et
al.,
2016;
Paiva
et
al.,
2014).
Consequently,
the
potential
application
of
this
solvent
in
the
extraction
of
bio-
logically
active
compounds
should
be
accompanied
by
the
evaluation
of
its
environmental
impact,
in
order
to
develop
a
truly
environmentally
friendly
process.
Moreover,
if
the
bio-
logical
activity
of
a
plant
extract
is
one
of
the
research
goals,
possible
antioxidative
activity
of
the
NADESs
should
be
con-
sidered.
Previous
studies
indicate
that
NADESs
could
enhance
the
antioxidative
activities
of
plant
extracts,
which
could
be
explained
by
the
reactive
oxygen
species
scavenging
activi-
ties
of
the
NADESs
itself
or
NADES
forming
compounds
(Nam
et
al.,
2015;
Radoˇ
sevi´
c
et
al.,
2016).
It
has
been
proposed
that
NADESs
formed
from
compounds
with
proven
pharmacolog-
ical
effects,
such
as
an
amino
acid
or
an
organic
acid,
could
also
have
similar
properties,
indicating
that
not
only
physic-
ochemical
characteristics
of
solvents,
but
also
their
biological
activity,
could
be
fine-tuned
(Radoˇ
sevi´
c
et
al.,
2016).
NADES
choice
is
followed
by
the
selection
of
an
extraction
method,
which
also
significantly
contributes
to
the
extraction
efficiency.
When
methods
for
green
extraction
are
consid-
ered,
the
reduction
of
energy
consumption
by
using
innovative
technologies
(e.g.
ultrasound
extraction
(UAE),
microwave
extraction
(MAE),
negative
pressure
cavitation
method)
should
be
taken
into
account.
These
innovative
technologies
have
been
recognized
as
an
excellent
energy
source
for
promot-
ing
extraction
efficiency
(Chemat
et
al.,
2012).
Several
studies
showed
that
NADESs
are
compatible
with
those
technolo-
gies
and
that
the
optimization
of
the
process
parameters
by
experimental
design
based
on
response
surface
methodology
was
conducted.
Irrespective
of
extraction
methods
chosen,
the
common
optimised
process
parameters,
were
extraction
time,
extraction
temperature
and
solvent
to
solid
ratio
(Wei
et
al.,
2015;
Qi
et
al.,
2015;
Li
et
al.,
2015;
Jeong
et
al.,
2015a;
Cvjetko
Bubalo
et
al.,
2016;
Bosiljkov
et
al.,
2017).
The
decrease
in
NADES
viscosity
at
elevated
temperatures
facilitates
the
penetration
of
the
NADES
into
the
plant
matrix,
leading
to
more
destruction
of
the
intermolecular
interaction,
and
thus
enhancing
the
dissolution
of
the
target
molecules
(Li
et
al.,
2015;
Wei
et
al.,
2015).
On
the
other
hand,
plant
bioactive
compounds
are
usually
thermosensitive,
thus
the
optimiza-
tion
of
temperature,
as
well
as
time
extraction,
are
necessary.
In
addition,
NADESs
could
also
be
used
in
headspace-solvent
microextraction
as
a
solvent-minimized
extraction
technique
for
the
extraction
of
volatile
compounds
(Tang
et
al.,
2015).
The
compatibility
of
NADESs
with
other
innovative
technol-
ogy,
such
as
supercritical
fluids,
as
a
two-phase
separation
system
should
also
be
considered.
Based
on
the
aforementioned,
the
green
extraction
of
plant
bioactive
compounds
in
a
biorefinery
could
be
based
on
the
utilization
of
NADESs.
However,
to
our
current
knowledge
there
are
no
such
processes
on
the
industrial
scale.
In
order
to
include
NADESs
in
both
new
and
existing
processes,
eco-
nomic
and
environmental
aspects
of
NADESs
should
still
be
considered.
The
cost
of
NADESs
is
comparable
to
conventional
solvents,
and
their
production
could
be
classified
as
a
sustain-
able
process
(Bi
et
al.,
2013;
Paiva
et
al.,
2014).
Nonetheless,
several
other
issues
should
be
taken
into
account,
includ-
ing
the
recovery
of
target
compounds
and/or
the
recyclability
of
NADESs,
prior
to
the
transfer
of
the
methodology
on
a
larger
scale.
The
almost
zero
vapour
pressure
of
the
NADESs

68
Food
and
Bioproducts
Processing
1
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9
(
2
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1
8
)
52–73
could
pose
a
huge
problem
when
the
recovery
of
the
target
compounds
is
needed,
especially
on
the
industrial
scale
(De
Oliveira
Vigier
et
al.,
2015).
So
far,
several
approaches
for
the
recovery
of
target
compounds,
such
as
solid
phase
extrac-
tion
and
the
application
of
anti-solvents,
recrystallization
and
adsorption
chromatography
have
been
reported
(Dai
et
al.,
2013b;
Nam
et
al.,
2015;
Jeong
et
al.,
2015b;
Huang
et
al.,
2017).
Jeong
et
al.
(2015b)
used
hydrophilic-lipophilic
−based
sorbent
to
recover
the
extracted
ginsenoside
from
NADESs
using
a
sim-
ple
procedure
including
the
loading
of
extracts
and
washing
with
water,
followed
by
elution
with
ethanol
with
full
recov-
ery.
Solid
phase
extraction
could
be
used
for
other
interesting
plant
bioactive
compounds,
using
simple
changes
of
the
solid
phase
for
particular
compounds
(Li
et
al.,
2015).
A
success-
ful
application
of
anti-solvents
method
was
also
reported,
by
using
water
as
the
most
efficient
anti-solvent
with
the
recov-
ery
of
95.1%
of
rutin
(Huang
et
al.,
2017).
Also,
the
recyclability
of
reused
NADESs
was
reported
using
the
simple
evapora-
tion
of
water
from
NADESs
following
the
recovery
of
rutin.
The
extraction
efficiency
of
choline
chloride:
glycerol
recycled
once,
twice,
three
times
was
92%,
87%
and
81%,
respectively
of
that
of
the
original
solvents.
A
similar
result
was
obtained
for
recycled
NADESs
by
lyophilisation
of
the
aqueous
solu-
tion
of
NADESs
produced
during
the
recovery
of
ginsenoside
(Jeong
et
al.,
2015b).
However,
recovery
and/or
recycling
after
extraction
and
scale-up
issues
should
be
definitely
studied
in
more
details
if
we
want
to
use
this
solvent
more
widely
on
the
industrial
scale.
4.
Future
trends
Nowadays,
we
cannot
find
a
production
process
in
the
food,
cosmetic,
pharmaceutical,
perfume,
or
chemical
industry
which
does
not
use
extraction
processes.
Recent
trends
in
extraction
techniques
have
largely
focused
on
finding
solu-
tions
that
minimize
the
use
of
harmful
solvents
and
allow
the
use
of
alternative,
so
called
“green”
solvents,
and
renewable
natural
products
that
ensure
safe
and
high
quality
extracts.
Safety,
environmental
and
economic
aspects
are
forcing
the
industry
to
turn
to
greener
extraction
techniques,
such
as
SFE,
SWE,
and
NADES.
The
future
of
SFE
is
surely
on
the
large
scale
for
a
lot
of
new
industrial
applications
(food,
cosmetic,
pharmaceutical
etc.),
thanks
to
the
many
benefits
of
CO2as
a
solvent
mentioned
in
this
review.
SWE
has
many
advantages
over
conventional
technolo-
gies.
Aside
from
that,
the
unique
properties
of
subcritical
water,
the
possibilities
for
the
selective
extraction
by
alter-
ing
temperature,
and
work
with
widely
available
and
low
cost
green
extraction
solvents,
makes
this
extraction
technology
the
technology
of
the
future.
Challenges
in
SWE
present
today
should
be
focused
on
a
scale
up
on
the
industrial
level
and
a
decrease
of
investment
costs.
Furthermore,
NADESs
have
unique
physicochemical
properties
and,
thanks
to
the
possi-
bility
of
designing
their
properties
for
a
particular
purpose,
their
low
ecological
footprint
and
attractive
prices,
they
have
become
increasingly
interesting
to
both
the
academia
and
the
industry.
However,
green
solvents
are
undoubtedly
the
sol-
vents
of
future
industry.
Acknowledgment
This
work
is
supported
by
the
Croatian
Science
Foundation
under
the
project
No.
9550.
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