Original
research
article
Improved
extraction
of
green
tea
components
from
teabags
using
the
microwave
oven
Quan
V.
Vuong
*
,
Sing
P.
Tan,
Costas
E.
Stathopoulos,
Paul
D.
Roach
School
of
Environmental
and
Life
Sciences,
University
of
Newcastle,
Ourimbah,
NSW
2258,
Australia
1.
Introduction
Green
tea
(Camellia
sinensis)
is
an
abundant
source
of
catechins,
which
are
strong
antioxidants
that
have
been
receiving
consider-
able
interest
for
their
potential
benefits
in
human
health
and
food
preservation
(Khan
and
Mukhtar,
2007;
Vuong
et
al.,
2010,
2011d).
For
example,
the
catechins
have
been
linked
with
protection
against
cardiovascular
disease
(CVD)
(Kuriyama,
2008).
Various
catechin
extracts
from
green
tea
have
been
shown
to
be
active
in
humans;
they
lower
low
density
lipoprotein
(LDL)
cholesterol,
one
of
the
major
risk
factors
for
CVD
(Zheng
et
al.,
2011).
Other
studies
have
shown
that
the
mechanisms
of
actions
for
their
cholesterol-
lowering
effect
include
an
increase
in
the
LDL
receptor
and
a
decrease
in
cholesterol
synthesis
(Bursill
et
al.,
2001,
2007;
Bursill
and
Roach,
2006,
2007).
Therefore,
due
to
the
potential
benefits
of
the
green
tea
catechins,
several
studies
have
been
done
on
the
various
brewing
conditions
to
maximise
the
extraction
of
these
components
from
green
tea.
The
results
have
defined
optimal
water
brewing
conditions
including
the
temperature
being
maintained
at
80
8C
for
30
min
and
a
ratio
of
tea
to
water
of
1:20
g/mL
(Komes
et
al.,
2010;
Lin
et
al.,
2008;
Peterson
et
al.,
2005;
Vuong
et
al.,
2011b).
However,
these
optimisation
studies
focused
on
loose-leaf
green
tea
and
were
carried
out
under
laboratory
conditions.
These
conditions
are
very
different
from
household
brewing
habits,
where
tea
is
simply
brewed
in
boiled
water
and
left
at
room
temperature
for
a
short
time
( 3
min)
before
being
consumed
(Astill
et
al.,
2001).
Although
many
people
still
traditionally
prepare
their
green
tea
by
brewing
loose-leaf
tea
in
boiled
water,
a
more
popular
and
convenient
way
of
preparing
green
tea
now
is
simply
brewing
a
teabag
in
boiled
water
for
3
min,
as
suggested
by
the
teabag
manufacturers
(Astill
et
al.,
2001).
However,
compared
to
30
min
under
optimal
laboratory
conditions,
it
was
hypothesised
that
most
of
the
catechins
would
not
have
time
to
infuse
into
the
hot
water
during
the
short
suggested
brewing
time
of
3
min.
This
could
be
relevant
because
it
may
explain
why
results
from
epidemiologi-
cal
studies
have
shown
that
only
high
volumes
(5–10
cups/day)
of
green
tea
are
associated
with
health
benefits
(Kuriyama,
2008;
Ui
et
al.,
2009).
In
other
words,
consumers
may
not
get
the
full
health
benefits
of
drinking
green
tea
because
the
extraction
of
the
catechins
is
not
optimal
under
household
brewing
conditions.
Journal
of
Food
Composition
and
Analysis
27
(2012)
95–101
A
R
T
I
C
L
E
I
N
F
O
Article
history:
Received
7
March
2012
Received
in
revised
form
28
May
2012
Accepted
2
June
2012
Keywords:
Bioactive
non-nutrients
Caffeine
Camellia
sinensis
Catechins
Food
analysis
Food
composition
Food
processing
Green
tea
Hot
water
extraction
Microwave
assisted
extraction
Teabag
Theanine
A
B
S
T
R
A
C
T
The
green
tea
(Camellia
sinensis)
catechins
are
strong
antioxidants
linked
with
potential
health
benefits.
Based
on
previous
studies,
it
was
hypothesised
that
the
typical
household
conditions
for
brewing
green
tea
in
a
teabag
–
200
mL
freshly
boiled
water
for
2–3
min,
as
per
the
manufacturers’
instructions
–
were
not
sufficient
to
extract
all
the
catechins
and
that
a
household
microwave
oven
could
be
used
to
improve
the
extraction.
The
catechins
and
the
two
other
main
green
tea
components,
caffeine
and
theanine,
were
monitored
by
HPLC.
The
typical
household
conditions
only
extracted
62%
(61
mg/g
tea),
76%
(24
mg/g)
and
80%
(10
mg/g)
of
the
catechins,
caffeine
and
theanine,
respectively,
from
the
five
varieties
of
teabags
analysed.
However,
using
microwave
assisted
extraction
(MAE)
by
first
brewing
a
teabag
in
200
mL
freshly
boiled
water
for
0.5
min
before
irradiation
for
1
min
in
a
microwave
oven
(hot
MAE),
improved
the
extraction
of
the
catechins
and
caffeine
to
80%
(80
mg/g)
and
92%
(29
mg/g),
respectively,
although
the
extraction
of
theanine
was
not
affected.
Therefore,
the
hot
MAE
technique
could
help
maximise
the
extraction
of
the
catechins
for
those
who
consume
green
tea
for
the
potential
health
benefits
of
the
catechins.
ß
2012
Elsevier
Inc.
All
rights
reserved.
*
Corresponding
author.
Tel.:
+61
2
4348
4129;
fax:
+61
2
4348
4145.
E-mail
address:
van.vuong@uon.edu.au
(Q.V.
Vuong).
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lists
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Journal
of
Food
Composition
and
Analysis
jo
u
rn
al
ho
m
epag
e:
ww
w.els
evier
.c
om
/lo
cat
e/jfc
a
0889-1575/$
–
see
front
matter
ß
2012
Elsevier
Inc.
All
rights
reserved.
http://dx.doi.org/10.1016/j.jfca.2012.06.001