vegetable vs. vegetables - hkasme.org20project.pdf · cells from high‐light damage by absorbing...
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Vegetable vs. Vegetables ‐ Detection of Heavy Metal Ions in Plants by Natural Pigments
Chan Sin Kan
Chiu Chun Yin
Lee Long Hei
Lee Po Lung
Liu Wan Ling
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Content
1. Introduction
1.1 Objectives P. 3
1.2 What is anthocyanin? P. 5
1.3 Design of experiment P. 6
2. Experimental P. 8
3. Results and discussions
3.1 Absorption spectrum of different vegetables or fruit
extracts P. 10
3.2 Response of anthocyanin to different metal ions P. 12
3.3 Detection limit of Pb2+, Cu2+ and Fe3+ by blueberry
extract and purple cabbage extracts P. 15
3.4 Absorbance spectrum of purple cabbage extract with
different concentrations of Pb2+, Cu2+ and Fe3+ P. 17
3.5 Growth of Rohdea Japonica P. 19
3.6 Using anthocyanin as a probe to find out the metal ions
absorbed in the plant P. 21
4. Conclusion P. 22
5. References P. 23
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1. Introduction
1.1 Objectives
Vegetable is our important diet, but do you know whether the
vegetables entering our body are non‐polluted? Polluted vegetable is
one of the major concerns of HK citizen. These vegetables are usual
polluted by different metal ions which coming from industrial discharge
in some areas in China. Fig. 1 shows the result of a survey done by a
press media on the content of lead in imported vegetables.
Fig.1 A newspaper cutting of vegetables polluted by lead.
From the survey, although the lead content of vegetables is lower than
the standard of HK, it is still higher than the level of standard of Australia
and European Union.
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Heavy metals do no good but harm to humans. They can disturb
important biochemical processes, constituting an important
threat for the health of humans. The accumulation of these heavy
metals can cause serious health conditions, such as autism, infertility,
dementia, thyroid problems, pathologicalevents, chronic
inflammatory disease, immune system disorders, cardiovascular
diseases, and even cancer. Other effects from heavy metal toxicity
include birth defects, constipation, anemia, liver disease, hypertension,
seizures, and insomnia. In other words—heavy metal toxicity is a very
serious concern.
Although metal ions have significant impact on our health, their
detection is time consuming and requires sophisticated instruments.
Therefore in this project, we are going to use anthocyanin, which is a
common pigment in vegetables, as a simple probe for the presence of
metal ions in vegetable. We also hope this cheap and easy method
allows all consumers to test whether vegetables they are going to eat are
heavily polluted with metal ions or not.
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1.2 What is anthocyanin?
Anthocyanin(Fig.2) can be easily find in fruit like blackberry, eggplant
peel, black rice, Concord grape, red cabbages, and violet petals.
Fig.2 Structure of Anthocyanin
Fruit containing anthocyanin gives an attractive skin to attract animals,
which may eat the fruits and disperse the seeds. In photosynthetic
tissues. Anthocyanin has been shown to act as a "sunscreen", protecting
cells from high‐light damage by absorbing blue‐green and ultraviolet
light, thereby protecting the tissues from photoinhibition, or high‐light
stress.
Anthocyanin is also known for different color at different pH. It usually
appears as pink in color when acidic, purple in color when neutral and
greenish yellow when alkaline.
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Fig.3 The binding between anthocyanin and metal ions.
Anthocyanin changes color too when adding on different
concentration of metal ions. It forms dative bond with metal ion (Fig.3)
and changes the structure of anthocyanin, this cause the change of color
of anthocyanin.
1.3 Design of experiment
We choose vegetables and fruits such as beetroot, purple cabbage
and blueberry as a source of anthocyanin. In each extraction, 50 grams
of vegetable or fruits are crushed and then extracted with alcohol. The
alcohol extracts are filtered and stored in dark to prevent decomposition
of anthocyanin by light.
The amount of anthocyanin is determined by spectrometer.
Anthocyanins show an absorption maxima in the range of 500‐600 nm.
By Beer’s Law, the concentration of anthocyanin in the extracts is
proportional to absorbance. It would be the best if we can obtain the
spectra with pure anthocyanins. However, they are not commercially
available. Therefore, instead of determining the concentration of
anthocyanin, we fix the absorbance of absorption peak to certain value,
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say, 0.2, by proper dilution, so that the concentration of anthocyanins in
different extracts are comparable.
We selected seven metal ions (Ni2+,Pb2+,Zn2+,Cu2+,Fe3+,Cd2+ and Co2+)
to investigate the response of anthocyanins towards these metal ions.
For extracts with drastic color change, we will investigate the detection
limit of these metal ions.
Finally, we use Rohdea japonica to mimic the vegetables or plants
irrigated with industrial waste‐contaminated water. We would like to
investigate the feasibility of using anthocyanin as a probe to detect the
metal ions in the vegetables.
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2. Experimental
Preparation of solution
0.5M metal ion solutions Fe3+, Pb2+, Cu2+, Zn2+, Cd2+, Co2+, Ni2+ are
prepared by dissolving suitable amount of FeCl3, Pb(NO3)2, CuSO4,
ZnCl2,CdCl2, CoCl2 and NiSO4 in 100cm3 distilled water.
Extraction of anthocyanin
50g vegetables are cut into pieces. Then they are mixed with alcohol
and crushed in a mortar. Extract is filtered and then kept in dark. The
extract is freshly prepared every 3 to 5 days.
Action of different metal ions on anthocyanin
We use spectrometer to find out the absorption maxima of the
anthocyanin. The absorbance of peak is fixed to 0.1 to 0.2 by proper
dilution. 1cm3 0.5M Fe3+, Pb2+, Cu2+, Zn2+, Cd2+, Co2+, Ni2+ solutions and
water are added to each well of a 24‐well plate. 1cm3 anthocyanin
extract is added to each metal ion solution. For control, 1cm3 water is
used instead of anthocyanin extract.
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Detection the limitation of Pb2+, Fe3+ and Cu2+ by
anthocyanin
0.5M, 0.05M, 5mM, 0.5mM, 0.05mM, 0.005mM of 1cm3 metal ion
solutions (Pb2+, Fe3+, Cu2+) and water are added to each well of the plate.
1cm3 anthocyanin with an absorbance of 0.2 is added to each metal ion
solution and water. 1 cm3 water is also used instead of metal ions in
control. For spectrometric analysis, mixtures are prepared by the same
method and their spectra are recorded by PASCO PS‐2600 Spectrometer.
Cultivation of plants in metal salt solution
3 Rohdea Japonica are immersed in 500cm3 metal ion solution(Fe3+,
Pb2+, Cu2+) of 2mM. Same amount of Rohdea Japonica are planted in
distilled water as control. Metal ion solutions and water are changed
every 2 days.
Test the presence of metal ions in Rohdea Japonica
Each Rohdea Japonica is washed under running water. Leaf and roof
of Rohdea Japonica are cut into pieces and burned to ash. 0.17g of ash is
mixed with 3ml extract with purple cabbage extract with absorbance of
0.15. The mixture is filtered and 1 ml of the filtrated is added each well
of a 24 well‐plate.
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3. Results and discussions
3.1 Absorption spectrum of different vegetables or fruit
extracts
Fig.4: Absorption spectra of purple cabbage extract in alcohol.
Fig.5: Absorption spectra of beet root extract in alcohol
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Fig.6: Absorption spectra of blueberry extract in alcohol.
From Fig. 4 to Fig. 6, all extracts show an absorption peak between
500‐600 nm. We can see that the absorption peak of beet root extract
and blueberry extract are both sharp and their absorption maximum
position are comparable (575nm and 578nm, respectively). However, the
absorption peak of purple cabbage extract is boarder and it is positioned
545nm.
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3.2 Response of anthocyanin to different metal ions
Fig.7: Color change of beetroot extract in 0.25M metal salt
From Fig7, we can see that the color of beetroot extract only change
slightly after adding metal ions except Ni2+, Cu2+ and Fe3+ turn to brown,
green and deep yellow, respectively.
0.25M metal
solution+water
0.25M metal
solution+beetroot
extract
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Fig.8: Color change of blueberry extract in 0.25M metal salt
From Fig. 8, we can see that the color change of blueberry extract
after is more significant compare with that of beet root extract after the
addition of metal ion. We can see that only Zn2+, Cd2+ and Cu2+ turn to red
or pink color. Ni2+ and Fe3+ turn to brown color. Pb2+ and Cu2+ turn to dark
purple color.
0.25M metal
solution+water
0.25M metal
solution+blueberry
extract
3
P. 14
Fig.9: Color change of purple cabbage extract in 0.25M metal salt
The color change of purple cabbage extract is even more significant
as shown in Fig. 9. Zn2+ Cd2+ and Cu2+ turn to purple color. Ni2+ turns to
brown color. Pb2+, Cu2+ and Fe3+ turn to deep purple color.
As both blueberry and purple cabbage extract shows the most
drastic color changes after the addition of metal ions, these two extracts
are chosen to study their detection limits on Pb2+, Cu2+ and Fe3+.
0.25M metal
solution+water
0.25M metal
solution+purple
cabbage extract
3
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3.3 Detection limit of Pb2+, Cu2+ and Fe3+ by blueberry
and purple cabbage extracts (a)
(b)
Fig.10: Mixture of (a) blueberry and (b) purple cabbage extract and Pb2+, Cu2+ and
Fe3+ at different concentrations
Cu2+
Fe3+
Pb2+
0.25M 0.025M 25mM 2.5mM 0.25mM 0.025mM
Fe3+
Pb2+
0.25M 0.025M 25mM 2.5mM 0.25mM 0.025mM
water
water
Cu2+
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From Fig. 10 (a) and (b), we can see that both blueberry and purple
cabbage extract have significant color change when the concentration of
metal ion solution down to 25mM. It seems that the anthocyanines in
both blueberry and purple cabbage bind to iron(III) ion strongly as shown
by their intense color at 25mM compare with other two metal ions.
Although both blueberry and purple cabbage extract have
comparable detection limits, purple cabbage gives a bigger contrast than
that of blueberry extract. Therefore, we investigate the action between
we use Pb2+ Cu2+ and Fe3+ and purple cabbage by spectroscopic method.
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3.4 Absorption spectrum of purple cabbage extract
with different concentration of Pb2+ Cu2+ and Fe3+ (a) (b)
(c)
Fig.11 Absorbance spectrum of purple cabbage extract with (a) lead(II), (b)copper(II)
and (c) iron(III) ion
As shown in Fig. 11(a), a new peak at 583nm appears gradually as the
concentration of lead(II) ion increases. This may responsible for the deep
purple color of the cabbage.
On the other hand, an absorption peak 538nm appears when copper(II)
ion is added to the extract. In addition, there is a new broad peak at
789nm, which is absent in lead(II) complex. In addition, the absorbance
increases drastically when the concentration reaches 25mM.
0.25M
0.025M
25mM
2.5mM
0.25mM
0.025mM
538 583.7
789
0.25M
0.025M
25mM
2.5mM
0.25mM
0.025mM
585
0.25M
0.025M
25mM
2.5mM
0.25mM
0.025mM
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The absorbance of purple cabbage with iron(III) ion has no significant
changes. When the concentration of iron(III) ion reaches 25 mM, its
absorption spectrum changes abruptly together with emergence of a
new, intense absorption peak at 585 nm. It seems that the
iron(III)‐anthocyanine complex is not formed until iron(III) ion
concentration reaches to a certain value, which is very different from
that of other two metal ions. This also explains why anthocyanine in
purple cabbage extract gives more intense color in the presence of
25mM iron(III) solution when compare with that with copper(II) and
lead(II) ions in Fig. 10(b).
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3.5 Growth of Rohdea Japonica in different metal ion
solutions Day 1 Day 3
Day 6 Day 8
Day 10 Day 10 (whole plant)
Fig. 12 Growth of Rohdea Japonica in Cu2+, Fe3+, water and Pb2+ (from left to right.
Metal ion concentration = 2mM.
In order to find out the feasibility of using purple cabbage extract as
a probe for detecting heavy metal ions in vegetables, we use Rohdea
Japonica as a model plant. Fig. 12 shows its growth in different metal ion
solutions with water as a control. All the plants looked healthy on day 1
and day 3. Nonetheless, the leaves of the plants cultivated in metal ion
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solutions seemed stop to grow starting from day 6. Among these, the
plant cultured with copper(II) ion began to turn yellow. The growth
difference is more significant on day 10, and the leaves of the plant with
copper(II) salt start to wilt. Also we can see that the roots of plants which
planted in metal ion solutions turned brown to different extents. This
show these metals ions exhibit different toxicity to Rhodea Japonica.
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3.6 Using anthocyanin as a probe for the presence of
metal ions in plant.
The Rohdea Japonica are washed under running water to wash away
any metal salts adsorbed on the surface of the plant. The roots, stems
and leaves are cut into separately and burnt in order to release metal
ions from the plant tissue. However, the stems cannot be burnt into ash
with Bunsen burner flame even with 10 minutes of direct burning.
Therefore only root and leaves are collected for further studies.
After burning, the ash of the plants are weighted and mixed with
3ml of purple cabbage extracts. 1ml of filtered mixture is added to a 24
well plate as shown in Fig. 13.
Fig.13 Different parts of plant absorbed with metal ions solution burned and mixed
with purple cabbage extract
Extract
only Water Pb2+ Cu2+ Fe3+
Root
Leaf
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The color of extract of the ashes from Rohdea Japonica which has
been planted in water turned from purple to green. It may be due to
change of pH by the ash. The color of extract changes to deep brown
with the ashes of both root and leaves from the plant which has been
cultivated in Cu2+ salt. The color is similar to the mixture between extract
and pure metal salt. Although the color change for lead(II) and iron(III)
salts are not significant, there may be some other reason behind such as
the difference in uptake of metal ions by the plant.
4. Conclusion
We have demonstrated that anthocyanines in many vegetables and
fruits can bind with different metal ions to give intense colors. Among
these, anthocyanine from purple cabbage gives significant color change
in the presence of copper(II), lead(II) and iron(III) ions with concentration
down to 25 mM. We have seen that purple cabbage extract can detect
the copper(II) ion absorbed in root and leaves of Rhodea Japonica.
Although different plants may have different uptakes on the same metal
ion, our work successfully demonstrates the possibility of using purple
cabbage extract to detect the presence of metal ions in plants. In our
future works, we will explore different ways to optimize the testing
process, especially the treatment of the plant. For example, we may use
blender to obtain Rohdea Japonica extract instead of burning into ash, or
even blend it with purple cabbage to observe any color change.
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5. References http://cat.inist.fr/?aModele=afficheN&cpsidt=785410
https://www.engg.ksu.edu/CHSR/outreach/resources/docs/15HumanHe
althEffectsofHeavyMetals.pdf
http://www.academia.edu/543847/Effect_of_Toxic_Metals_on_Human_
Health
http://www.doctorshealthpress.com/general‐health/heavy‐metals‐the‐h
idden‐harmful‐ingredient‐even‐in‐healthy‐foods
http://en.wikipedia.org/wiki/Anthocyanin
http://en.wikipedia.org/wiki/Beer%E2%80%93Lambert_law
http://en.wikipedia.org/wiki/Spectrometer
http://en.wikipedia.org/wiki/Absorbance