Effect of foliar application of selenium on the antioxidant activity of aqueous and ethanolic extracts of selenium-enriched rice


Xu, J.; Hu, Q.

Journal of Agricultural and Food Chemistry 52(6): 1759-1763

2004


Selenium fertilizer was foliar applied to determine the effects of antioxidant activity of seleniumenriched rice assessed by a,α-diphenyl-P-picylhydrazyl (DPPH) radical scavenging and the ferric thiocyanate (FTC) method. Results showed that selenium concentration in rice was significantly enhanced dose dependently. Aqueous or ethanolic extracts of rice displayed significantly higher antioxidant activity against lipid peroxidation. The activities of aqueous extracts were significantly higher than those of ethanolic extracts and increased with the increasing selenium concentration in rice. The DPPH assay showed that the kinetic behaviors of aqueous extracts were complex and slow, while ethanolic extracts reacted quickly with DPPH radical. Aqueous extracts of rice exhibited higher antiradical efficiencies than ethanolic extracts, and rice (1.275 mg Se kg-1) presented the lowest EC50 values of 533.46±0.58,tig mL-1. As compared to rice extracts, all of the reference antioxidants showed more than 4-fold antiradical efficiencies than rice extracts. This radical scavenging activity was significantly correlated with selenium concentrations in rice (R=0.862, p<0.05), while ethanolic extracts were inversely correlated with selenium concentration in rice.

AGRICULTURAL
AND
FOOD
CHEMISTRY
J.
Agric.
Food
Chem.
2004,
52,
1759-1763
1759
Effect
of
Foliar
Application
of
Selenium
on
the
Antioxidant
Activity
of
Aqueous
and
Ethanolic
Extracts
of
Selenium
-Enriched
Rice
JUAN
XU
-14
AND
QIUHUI
HU
*
't
Key
Laboratory
of
Food
Processing
and
Quality
Control,
College
of
Food
Science
and
Technology,
Nanjing
Agricultural
University,
Nanjing
210095,
People's
Republic
of
China,
and
Department
of
Biology,
Changshu
College
of
Science
and
Technology,
Changshu
215500,
People's
Republic
of
China
Selenium
fertilizer
was
foliar
applied
to
determine
the
effects
of
antioxidant
activity
of
selenium
-
enriched
rice
assessed
by
a,a-diphenyl-P-picylhydrazyl
(DPPH)
radical
scavenging
and
the
ferric
thiocyanate
(FTC)
method.
Results
showed
that
selenium
concentration
in
rice
was
significantly
enhanced
dose
dependently.
Aqueous
or
ethanolic
extracts
of
rice
displayed
significantly
higher
antioxidant
activity
against
lipid
peroxidation.
The
activities
of
aqueous
extracts
were
significantly
higher
than
those
of
ethanolic
extracts
and
increased
with
the
increasing
selenium
concentration
in
rice.
The
DPPH
assay
showed
that
the
kinetic
behaviors
of
aqueous
extracts
were
complex
and
slow,
while
ethanolic
extracts
reacted
quickly
with
DPPH
radical.
Aqueous
extracts
of
rice
exhibited
higher
antiradical
efficiencies
than
ethanolic
extracts,
and
rice
(1.275
mg
Se
kg
-1
)
presented
the
lowest
EC
50
values
of
533.46
±
0.58
,tig
mL
-1
.
As
compared
to
rice
extracts,
all
of
the
reference
antioxidants
showed
more
than
4
-fold
antiradical
efficiencies
than
rice
extracts.
This
radical
scavenging
activity
was
significantly
correlated
with
selenium
concentrations
in
rice
(R
=
0.862,
p
<
0.05),
while
ethanolic
extracts
were
inversely
correlated
with
selenium
concentration
in
rice.
KEYWORDS:
Selenium;
extracts
of
Se
-enriched
rice;
antioxidant
activity
INTRODUCTION
Selenium
has
received
considerable
attention
as
an
essential
micronutrient
for
animals
and
the
human
body.
It
functions
in
the
active
site
of
a
large
number
of
selenium
-dependent
enzymes
such
as
GSH-Px
(1)
and
in
anticancer
and
other
physiological
functions
(2,
3).
A
lower
selenium
level
in
body
is
reported
to
be
responsible
for
high
incidences
of
cancer
and
disease.
However,
selenium
concentration
of
a
particular
food
may
be
variable
and
dependent
on
the
geographic
origin
of
the
soil
where
the
agricultural
crops
are
grown
(4).
Selenium
deficiency
is
still
a
very
serious
nutritional
and
health
problem
in
China
(5).
Therefore,
the
supply
of
selenium
to
livestock
through
forage
and
to
human
beings
through
food
has
been
a
practice
adopted
to
prevent
selenium
deficiencies
in
several
areas
(6).
Rice
is
one
of
the
leading
food
crops
of
the
world
and
is
the
staple
food
of
over
half
of
the
world's
population
(7).
Rice
is
an
excellent
source
of
complex
carbohydrates,
fiber
(brown
rice),
and
vitamins,
and
after
it
is
hulled,
the
polished
rice
has
fewer
nutrients
than
brown
rice
(8).
Many
studies
have
shown
the
antioxidant
and
low
cholesterol
levels
of
oil
extracts
from
rice
bran
(9-11).
However,
little
is
reported
on
the
physiological
*
To
whom
correspondence
should
be
addressed.
Fax:
86-25-4396431.
Email:
qiuhuihu@njau.edu.cn.
Nanjing
Agricultural
University.
*
Changshu
College
of
Science
and
Technology.
properties
of
polished
rice.
In
addition,
the
selenium
content
of
rice
was
lower,
and
the
mainly
rice
-based
diet
contributed
an
inadequate
amount
of
selenium
for
Chinese
inhabitants
(12).
In
our
previous
study,
we
have
shown
that
selenium
application
could
increase
selenium
content
from
0.025
±
0.011
,ttg
g
-1
in
regular
polished
rice
to
0.471-0.640
,ttg
g
-1
in
Se
-enriched
polished
rice
(13).
The
in
vivo
antimutagenic
assay
of
Se
-
enriched
rice
also
exhibited
a
significantly
higher
activity
than
that
of
regular
rice.
The
objective
of
this
study
is
to
explore
the
effect
of
foliar
application
of
selenium
fertilizer
on
selenium
content
in
rice
and
determine
whether
Se
-enriched
rice
presented
higher
antioxidant
activity
than
regular
rice
at
various
selenium
concentrations
using
a,a-diphenyl-P-picylhydrazyl
(DPPH)
radical
scavenging
and
the
ferric
thiocyanate (FTC)
method.
MATERIAL
AND
METHODS
Chemicals.
Chemicals
were
used
as
follows:
linoleic
acid
(ca.
99%)
(Wako
Chemical
Pure
Chemical
Industries
Ltd.,
Osaka,
Japan);
DPPH
(Aldrich
Chemical
Co.,
Milwaukee,
WI);
6-hydroxy-2,5,7,8-tetramethyl-
chroman-2-carboxylic
acid
(Trolox)
(Aldrich
Chemical
Co.
Milwaukee,
WI);
a-tocopherol
(Sigma
Chemicals
Co.,
St.
Louis,
MO);
and
butylated
hydroxyanisol
(BHA),
ammonium
thiocyanate,
and
ferrous
chloride
(Nanjing
Chemical
Industry,
Nanjing,
China).
Ethanol
and
other
reagents
were
of
analytic
grade
produced
in
Nanjing.
10.102
1
/
1
'0349836
CCC:
$27.50
©
2004
American
Chemical
Society
Published
on
Web
02/19/2004
1760
J.
Agric.
Food
Chem.,
Vol.
52,
No.
6,
2004
Xu
and
Hu
Preparation
of
Selenium
Fertilizer.
Lobster
waste
(20%),
chicken
excreta
(30%),
silkworm
excreta
(15%),
pig
excreta
(34%),
and
EM
(effective
microorganism)
bacterium
(1%)
were
mixed
and
allowed
to
ferment
for
about
2
weeks
in
a
methane
-generating
pit.
Se,
as
sodium
selenite
and
water,
was
added
to
the
mixed
fertilizer
and
well
-
distributed,
and
then,
fermentation
was
allowed
to
continue
for
4
weeks.
The
fermented
solution
was
filtered.
The
final
solution
contained
50
g
Se
L
-1
.
The
Se
-enriched
fertilizer
was
bottled
in
a
plastic
container
as
a
volume
of
100
mL
(12,
13).
Preparation
of
Regular
Rice
and
Selenium
-Enriched
Rice
Samples.
The
plot
experiment
was
conducted
in
May,
2001,
in
Kunshan
Country,
Jiangsu
Province.
The
cultivar
of
rice
was
R
109.
The
soil
pH
in
this
region
was
5.7,
and
the
total
selenium
content
was
0.326µg
Se
g
-1
of
soil.
Application
of
selenium
fertilizer
to
rice
was
detailed
by
Chen
(13)
on
September
9,
2001.
Rice
samples
with
three
different
selenium
concentrations
were
obtained
by
varying
the
concentrations
of
selenium
fertilizer.
When
being
thoroughly
tasseled,
the
grain
was
hand
harvested
on
October
30,
2001.
After
it
was
harvested,
the
grain
was
dried
at
50
°C,
then
hulled,
and
milled
into
powder
for
further
use.
Selenium
concentration
of
rice
was
analyzed
using
atomic
fluorescence
spectroscopy
(12).
Preparation
of
Rice
Aqueous
and
Ethanolic
Extracts.
Five
grams
of
ground
rice
was
extracted
with
100
mL
of
distilled
water
or
100
mL
of
75%
ethanol,
respectively.
Extractions
were
conducted
in
a
water
bath
with
a
constant
temperature
of
60
°C
for
3
h.
Each
sample
was
extracted
twice
with
the
same
volume
of
solvents.
The
mixture
was
filtered
and
combined.
The
filtrate
was
evaporated
to
dryness
in
vacuo
and
kept
frozen
for
antioxidative
assays.
Standard
Aqueous
and
Ethanolic
Rice
Extracts
Solution.
Twenty
micrograms
of
rice
extract
was
solublized
in
75%
ethanol
in
an
ultrasonic
water
bath
to
a
final
concentration
of
1000
yg
mL
-1
.
Determination
of
Antioxidant
Activity
with
the
FTC
Method.
Two
milliliters
of
1000
yg
mL
-1
rice
extract
or
2
mL
of
200
yg
mL
-1
antioxidants,
2
mL
of
2.51%
(w/v)
linoleic
acid
in
ethanol,
4
mL
of
0.05
mol
L
-1
of
phosphate
buffer
(pH
7.0),
and
2
mL
of
distilled
water
were
mixed
in
a
vial
of
10
mL
with
a
screw
cap
and
then
kept
in
a
40
°C
water
bath
in
the
dark.
A
0.1
mL
amount
of
the
above
mixture
was
added
to
9.7
mL
of
75%
(v/v)
ethanol
and
0.1
mL
of
30%
(w/v)
ammonium
thiocyanate.
After
5
min,
0.1
mL
of
0.02
mol
L
-1
ferrous
chloride
in
3.5%
(v/v)
hydrochloric
acid
was
added
to
above
mixture
and
then
kept
in
a
40
°C
water
bath
in
the
dark.
The
absorbance
of
mixture
was
measured
every
24
h
at
500
nm
until
an
unchangeable
absorbance
value
arrived.
The
FTC
method
was
described
in
detail
by
Kikuzaki
(14).
All
of
the
tests
were
performed
in
triplicate,
and
the
results
were
averaged.
Assay
of
DPPH
Radical
Scavenging
Activity.
The
antioxidant
activities
of
rice
extracts,
BHA,
a-tocopherol,
and
Trolox
were
determined
using
the
stable
radical,
DPPH
(15,
16).
Briefly,
0.1
mL
of
rice
extracts,
BHA,
Trolox,
and
a-tocopherol
was
added
to
3.9
mL
of
2
x
10'
mol
L
-1
ethanol
solution
of
DPPH
in
cuvette.
Absorbance
measurements
commenced
immediately.
The
decrease
in
absorbance
was
determined
at
517
nm
and
continuously
at
every
5
min
interval
with
a
spectrophotometer
until
the
reaction
reached
steady
state.
The
percentage
of
DPPH
remaining
at
the
steady
state
was
calculated
as
a
function
of
the
molar
ration
of
antioxidant
to
DPPH.
The
EC
50
value,
which
is
defined
as
the
amount
of
antioxidant
necessary
to
decrease
the
initial
DPPH
concentration
by
50%,
was
calculated
from
the
results.
All
of
the
tests
were
performed
in
triplicate,
and
the
results
were
averaged.
Statistics
Analysis.
One
way
analysis
of
variance
was
performed
on
the
data
using
SPSS
(Release
11.0).
Student's
t
-LSD
(least
significant
difference)
(P
<
0.05)
was
calculated
to
compare
the
means
of
the
different
samples.
RESULTS
AND
DISCUSSION
Effect
of
Selenium
Application
on
Rice
Selenium
Con-
centration.
Table
1
shows
that
selenium
foliar
application
to
rice
can
significantly
increase
its
total
selenium
concentration
(P
<
0.05).
The
total
selenium
concentration
in
regular
rice
was increased
from
0.027
to
0.435
1.275
,ttg
g
-1
.
Statistics
Table
1.
Effect
of
Selenium
Application
on
Total
Selenium
in
Polished
Ricea
applied
Se
concn
(mg
Se
L
-1
)
applied
Se
dose
(g
Se
ha
-1
)
total
Se
concn
(mg
kg
-1
)
0 0
0.027
±
0.001a
20
15
0.435
±
0.220
b
60
45
0.890
±
0.017b
80
60
1.275
±
0.099'
a
Within
the
same
column,
means
followed
by
different
letters
are
significantly
different
at
P
<
0.05.
analyses
showed
that
selenium
concentrations
in
rice
were
significantly
increased
with
the
increasing
selenium
dose
of
applied
fertilizer
(R
=
0.993,
P
<
0.007).
This
suggested
that
application
of
selenium
fertilizer
can
effectively
enhance
the
selenium
content
in
rice.
Antioxidant
Activities
of
Rice
Aqueous
or
Ethanolic
Extracts
Assayed
by
FTC
Method.
The
antioxidant
activity
of
rice
extracts,
determined
using
the
FTC
method,
was
compared
with
that
of
BHA,
a-tocopherol,
and
Trolox,
and
the
results
are
shown
in
Figure
1.
The
individual
activity
of
samples
showed
low
absorbance
values,
which
indicated
a
high
level
of
antioxidant
activity.
All
of
the
rice
extracts
delayed
oxidation
of
linoleic
acid
and,
on
the
basis
of
low
absorbance
values,
exhibited
higher
activity
than
control.
Also,
lipid
inhibitive
activities
of
rice
aqueous
extracts
were
higher
than
those
of
ethanolic
extracts
except
of
rice
aqueous
extract
(0.027
mg
Se
kg
-1
).
However,
aqueous
extracts
and
ethanolic
extracts
showed
the
different
pattern
of
activity
(Figure
la).
Antioxidant
activities
of
rice
aqueous
extracts
decreased
in
the
following
order:
rice
(1.275
mg
Se
kg
-1
)
>
rice
(0.890
mg
Se
kg
-1
)
>
rice
(0.435
mg
Se
kg
-1
)
>
rice
(0.027
mg
Se
kg
-1
).
All
ethanolic
extracts
displayed
significantly
higher
activity
than
control
without
antioxidants.
However,
there
is
no
signifi-
cant
difference
between
all
ethanolic
exgtracts
(Figure
lb).
Comparisons
of
antioxidant
activities
were
also
made
between
rice
extracts
and
reference
antioxidants
including
BHA,
a-to-
copherol,
and
Trolox
(an
aqueous
analogue
of
a-tocopherol)
(Figure
lc).
The
activity
decreased
in
the
following
order:
aqueous
extract
of
rice
(1.275
mg
Se
kg
-1
)
>
BHA
>
Trolox
>
ethanolic
extract
of
rice
(0.435
mg
Se
kg
-1
)
>
a-tocopherol.
a-Tocopherol
appeared
to
exert
a
lower
antioxidant
potential
than
rice
extracts,
BHA,
and
Trolox.
During
the
first
3
days,
the
aqueous
extract
of
rice
(1.275
mg
Se
kg
-1
),
BHA,
and
Trolox
showed
no
difference
in
delaying
oxidation
of
lipid.
From
the
fourth
day,
however,
the
antioxidant
effect
of
aqueous
extract
on
lipid
oxidation
was
significantly
higher
than
that
of
BHA
and
Trolox.
Antioxidant
Activity
of
Rice
Extracts
Assessed
by
Scav-
enging
DPPH
Radical
Method.
The
DPPH
radical
is
consid-
ered
to
be
a
model
of
a
stable
lipophilic
radical.
Antioxidants
react
with
DPPH,
reducing
a
number
of
DPPH
molecules
equal
to
their
number
of
available
hydroxyl
groups.
Therefore,
the
absorption
at
517
nm
was
proportional
to
the
amount
of
residual
DPPH*.
The
kinetic
classification
according
to
the
time
at
the
steady
state
has
been
reported
as
follows:
rapid,
<5
min;
intermediate,
5-30
min;
and
slow,
>30
min
(16).
Figure
2
illustrates
the
kinetic
behavior
of
rice
extracts
and
antioxidants
as
radical
scavengers
toward
DPPH*.
Different
kinetics
was
observed.
In
our
study,
all
of
the
rice
samples
exhibited
significant
antiradical
activity.
During
the
first
15
min,
Antioxidant
Activity
of
Selenium
-Enriched
Rice
J.
Agric.
Food
Chem.,
Vol.
52,
No.
6,
2004
1761
Absorbance
(X.-500nm)
0.5
0.45
0.4
0.35
0.3
0.25
0.2
0.15
0.1
0.05
a
0
1
2
3
4
Time
(day)
5
6
-X-Control
-M-
Rice
(0.027mg
kg
-1)
-A-Rice
(0.435
mg
kg
-1)
-0-Rice
(0.890
mg
kg
-1)
-t:3-
Rice
(1.275
mg
kg
-1)
0.5
0.45
P
E
0.4
0.35
0.3
g
0.25
0.2
2
0.15
<
0.1
0.05
0
-X-Control
1
2
Absorbance
(k=500nm)
0.5
0.425
0.35
0.275
0.2
0.125
0.05
b
0
1
2
3
4
5
6
Time
(day)
-x-Control -0-
Rice
(0.027mg
kg
-1)
-A-
Rice
(0.435
mg
kg
-1)
-0-
Rice
(0.890
mg
kg
-1)
-)K-
Rice
(1
.275
mg
kg
-1)
3
Time
(day)
4
5
6
-M-
Aqueous
rice
(1.275
mg
kg
-1)
-A-
Ethanolic
rice
(0.435
mg
kg
-1)
-N-a-Tocopherol
-0-Trolox
-Ct-
BHA
Figure
1.
Antioxidant
activity
of
rice
aqueous
extracts
and
ethanolic
extracts,
BHA,
Trolox,
and
a-tocopherol,
as
measured
by
the
thiocyanate
method.
(a)
Aqueous
extracts
of
rice
with
various
selenium
concentrations;
(b)
ethanolic
extracts
of
rice
with
various
selenium
concentrations;
and
(c)
comparison
of
antioxidant
activities
of
aqueous
extract
of
rice
(1.275
mg
Se
kg
-1
),
ethanolic
extract
of
rice
(0.435
mg
Se
kg
-1
),
and
reference
antioxidants.
the
reaction
between
DPPH
radical
and
aqueous
extracts
was
rapid
and
rice
(0.027
mg
Se
kg
-1
)
reached
to
the
steady
state
in
15
min
(Figure
2a).
Afterward,
the
absorbance
decrease
for
all
extracts
was
rather
weak.
However,
for
ethanolic
extracts,
the
reaction
reached
a
plateau
in
5
min
(Figure
2b).
Therefore,
the
rice
aqueous
extracts
and
ethanolic
extract
(0.027
mg
Se
kg
1
)
were
slow
and
the
rest
of
the
ethanolic
extracts
were
rapid.
Three
antioxidants
reacted
rapidly
with
DPPH
radical
and
BHA,
and
Trolox
reached
the
steady
state
in
5
min
while
the
absorbance
of
a-tocopherol
was
stable
till
15
min
(Figure
2c).
This
result
was
a
little
different
from
data
reported
by
Sanchez
-
Moreno
(16)
in
that
the
kinetic
classification
of
BHA was
slow
and
a-tocopherol
was
intermediate.
EC
50
,
meaning
the
concentration
of
antioxidant
needed
to
decrease
by
50%
the
initial
substrate
concentration,
is
a
parameter
widely
used
to
measure
the
antiradical
efficiency
(17-19).
The
lower
the
EC
50
is,
the
higher
the
antioxidant
power
is.
The
values
of
rice
extracts,
BHA,
a-tocopherol,
and
Trolox
are
compared
and
shown
in
Table
2.
Except
for
rice
aqueous
extract
(0.027
mg
Se
kg
1
),
all
of
the
aqueous
extracts
possessed
the
lower
EC
50
than
their
ethanolic
extract.
Rice
aqueous
extract
(1.275
mg
Se
kg
-1
)
was
the
most
efficient
by
the
lowest
ECso
values
of
553.46
mg
kg
among
all
of
the
extracts,
and
the
activity
decreased
in
the
order:
rice
(1.275
mg
Se
kg
-1
)
>
rice
(0.890
mg
Se
kg
1
)
>
rice
(0.435
mg
kg
-1
)
>
rice
(0.027
mg
Se
kg
-1
).
For
ethanolic
extracts,
the
activity
followed
the
increasing
order:
rice
(1.275
mg
Se
kg
-1
)
<
rice
(0.890
mg
Se
kg
-1
)
<
rice
(0.027
mg
Se
kg
-1
)
<
rice
(0.435
mg
Se
kg
-1
).
This
behavior
was
similar
to
the
above
results
determined
by
the
FTC
method.
However,
reference
antioxidants
provided
rather
lower
EC
50
values
than
rice
extracts,
in
other
words,
meaning
more
than
4
-folds
antiradical
efficiencies
than
rice
extracts.
BHA
has
the
lowest
EC
50
of
114.45
±
0.50µg
mL
-1
among
the
three
antioxidants
and
Trolox
followed
as
the
second.
This
result
was
in
agreement
with
the
previous
repot
that
BHA
and
a-tocopherol
had
EC
50
values
of
93
g
antioxidant
kg
-1
DPPH'
and
201
g
antioxidant
kg
-1
DPPH
(16).
Shimada
reported
that
the
activity
of
antioxidants
(compounds)
corre-
sponds
to
the
number
of
hydrogens
available
for
donation
by
hydroxyl
groups
(20).
Also,
it
is
well-known
that
monophenols
are
less
efficient
than
the
polyphenols,
but
in
BHA,
the
methoxy
substitution
increases
substantially
the
antioxidant
power
of
monophenols.
Because
of
the
complex
nature
of
plants,
extracts
cannot
be
evaluated
by
only
a
single
method.
In
this
study,
we
adopted
the
FTC
method
to
determine
the
ability
to
inhibit
lipid
oxidation
and
DPPH
radical
scavenging
assay.
On
the
basis
of
Figure
lc,
there
was
little
gap
between
the
rice
extracts
and
the
reference
antioxidants
assayed
by
the
FTC
method.
However,
large
gaps
were
found
in
Table
2.
This
difference
may
be
due
to
the
unequal
concentrations
of
antioxidants.
The
antioxidant
activity
of
rice
extracts
was
assayed
at
the
concentrations
of
1
mg
mL
-1
,
and
antioxidants
were
assayed
at
200
,ttg
mL
-1
.
Therefore,
it
is
noteworthy
that
the
FTC
method
and
DPPH
radical
scavenging
kinetics
gave
false
-negative
results.
EC
50
values
present
the
real
antioxidative
potential
of
antioxidants,
regardless
of
their
concentrations
tested.
Effect
of
Selenium
Concentration
in
Rice
on
Its
Antioxi-
dant
Potential.
The
associations
between
rice
selenium
con-
centration
and
its
antioxidant
activity
were
also
investigated
in
this
study.
Table
2
shows
that
the
EC
50
values
of
rice
aqueous
1762
J.
Agric.
Food
Chem.,
Vol.
52,
No.
6,
2004
Xu
and
Hu
a
b
Absorbance
(2.=5
17nm)
1.6
1.6
r
1.4"\
1.4
1.2
1.2
0.8
r
1
0.6
1)
0.8
AX
0.4
,
0.6
0.2
0.4
0
0.2
0
15
30
45
60
75
90
105
0
Time
(min)
-*-Control -M-Rice(0.027mg
kg
-1)
-A-Rice(0.435
mg
kg
-1)
--Rice(0.890
mg
kg
-1)
-0-Rice(1.275
mg
kg
-1)
1.6
1.4
0
15
30
45
60
75
90
105
Time
(min)
-•-Control
-0-
Rice(0.027mg
kg
-1)
Rice(0.435
mg
kg
-1)
-X-
Rice(0.890
mg
kg
-1)
-)K-
Rice(1.275
mg
kg
-1)
C
0.8
0.6
0.4
0.2
0
0
15
30
45
-0-Control
-X- BHA
X X X
X
X
X
60
75
90
105
Time
(min)
Aqueous rice(1.275 mg kg-1) -0- Rice(0.435 mg kg-1)
-X- a-Tocopherol -0- Trolox
Figure
2.
Kinetic
behaviors
of
radical
scavenging
activity
of
rice
extracts
and
three
antioxidants.
(a)
Rice
aqueous
extracts;
(b)
rice
ethanolic
extracts;
and
(c)
aqueous
extract
of
rice
(1.275
mg
Se
kg
-1
),
ethanolic
extract
of
rice
(0.435
mg
Se
kg
-1
),
and
antioxidants.
Table
2.
Radical
Scavenging
Activities
of
Rice
Extracts
and
Antioxidants
Expressed by
EC
50
a
sample
rice
(0.027
mg
kg
-1
)
rice
(0.435
mg
kg
-1
)
rice
(0.890
mg
kg
-1
)
rice
(1.275
mg
kg
-1
)
Trolox
a-tocopherol
BHA
EC
50
(irg
mL
-1
)
aqueous
extract
ethanolic
extract
802.91
±
3.69a
868.33
±
9.35a
597.65
±
0.68
b
860.23
±
4.94a
557.23
±
4.74'
918.90
±
7.25
b
533.46
±
0.58c
996.77
±
8.53c
122.39
±
0.14
133.65
±
1.02
114.45
±
0.50
a
Within
the
same
column,
means
followed
by
different
letters
are
significantly
different
at
P
<
0.05.
extracts
decreased
with
the
increasing
selenium
concentration,
and
it
is
opposite
in
ethanolic
extracts
that
EC
50
increases
with
selenium
concentrations
in
rice.
EC
50
values
of
aqueous
extracts
are
lower
than
ethanolic
extracts.
After
statistical
analyses,
we
found
that
the
selenium
concentration
in
rice
was
significantly
inversely
correlated
with
its
EC
50
values,
which
indicated
that
selenium
has
a
dose
-dependent
effect
on
antioxidant
activities
of
rice
aqueous
extracts
(R
=
0.862,
P
<
0.006).
However,
in
ethanolic
extracts,
it
is
interestingly
found
that
with
increasing
selenium
concentration
in
rice,
the
antioxidant
activity
of
ethanolic
extracts
significantly
decreased
(R
=
0.906,
P
<
0.006).
Selenium
has
been
reported
to
enhance
the
antioxidative
system
in
ryegrass
at
low
concentrations
dose
responsively
(21).
Oxidative
stress
in
Se
-enriched
garlic
was
significantly
lower
than
that
in
regular
garlic,
and
the
antioxidant
activity
increased
with
selenium
concentration
in
a
hydroponic
soulition
(22).
Selenium
can
also
enhance
the
total
antioxidant
capacity
property
in
"Seoul"
lettuce
in
hydroponics
without
any
nutri-
tional
loss
(23).
Our
previous
studies
have
reported
that
selenium
enhanced
the
antioxidant
activity
of
green
tea
extracts
and
that
the
effect
is
dose
-dependent
(24).
In
polished
rice,
starch
accounted
for
76.60%
and
crude
protein
and
lipid
accounted
for
7.80
and
1.30%,
respectively.
Therefore,
selenium
might
be
responsible
for
the
higher
antioxidant
activity
of
Se
-enriched
rice.
Further
studies
are
needed
to
clarify
the
components
in
Se
-enriched
rice
responsible
for
its
antioxidant
activity.
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Received
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1,
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Revised
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received
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7,
2004.
Accepted
January
20,
2004.
The
Scientific
Ministry
of
China
under
Project
G1999011808-3
supported
this
research.
JF0349836