Republic Polytechnic Scientific
Thinking Programme 2008
Vitamin C content in local vegetables
and how cooking affects Vitamin C
content
Gan Eng Seng School Team 2
GAN ENG SENG SCHOOL
Aim
• To determine the concentration of Vitamin
C present in 4 common vegetables.
• To determine if the duration of boiling will
affect the concentration of Vitamin C in 1
of the 4 local vegetables.
GAN ENG SENG SCHOOL
Hypothesis
• Boiling will result in the decrease in the
concentration of Vitamin C. The longer the
duration, the lower the concentration of
Vitamin C left in the vegetable.
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Methods
•
4 different vegetables were selected to
determine the Vitamin C concentration
using iodometric titration.
Ascorbic acid + I2  2I- + dehydroascorbic acid
•
Excess iodine will then react with the
starch indicator to form the starch-iodine
complex, which marks the end point of
titration. This is when the first permanent
trace of dark-blue coloration is observed
due to the formation of the starch iodine
complex.
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Determining the concentration of the prepared
iodine solution
1.
2.
3.
4.
5.
Dilute 1 Redoxen Effervescence Vitamin C tablet (1000mg of
Vitamin C) in 1000ml of iced water.
Adding another 100m of iced water further dilutes 100ml of the
diluted solution.
25ml of this standard solution and 3ml of starch indicator solution
is pipette into a conical flask and titrated against the
iodine
solution.
Iodine solution was added slowly into the standard solution and
stopped when the first permanent trace of blue-black coloration is
observed.
Titration was repeated for a total of
3 times or more until concordant results
(within the range of 0.1cm3) were
obtained.
GAN ENG SENG SCHOOL
Determining concentration of Vitamin
C in 4 different vegetables
1.
2.
3.
4.
5.
Chop each type of vegetables
into fine pieces using a knife
on a chopping board.
Blend 100g of the chopped
vegetables and 200ml of iced
water for 2 minutes.
Iced water was added as the
heat generated by the blender
may destroy some of the
vitamin.
The blended mixture is
strained through a cheese
cloth and collected in a beaker.
The beaker was placed in ice
to keep the mixture cold.
Titration was carried
Determining the concentration
of vitamin C in green pepper
after boiling
1. The green peppers were
chopped into fine pieces using
a knife on a chopping board.
2. 100g of the chopped vegetables
were then added to boiling
water and was boiled for a fixed
duration (1min, 5min, 10min,
15min, 20min, 25min, 30min,
35min and 40min).
3. After boiling for a fixed duration,
the boiled green peppers were
removed and placed into the
blender.
4. Titration was then carried out
GAN ENG SENG SCHOOL
Concentration of vitamin C present in 4 common
vegetables.
Vegetable
Concentration of Vitamin C
Broccoli
(mg / 100g)
52.8
Cabbage
25.1
Carrot
11.6
Green Pepper
88.8
 Green pepper has the highest concentration of
vitamin C
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The effect of the duration of boiling on the concentration of
Vitamin C in green pepper
Change in concentration of Vitamin C
100
90
80
Concentration (mg/100g)
70
60
50
40
30
20
10
0
0
5
10
15
20
25
30
35
40
Time (min)
 The concentration of vitamin C decreases as the duration
of boiling increases
GAN ENG SENG SCHOOL
Significance of the experiment
• The group found evidence that cooking the
vegetables decreases the vitamin C content of
the vegetable. To retain the Vitamin C content,
we feel that it is necessary to keep the cooking
time to a minimum.
• Suggestions for Improvement
– The determination of Vitamin C content in the
vegetables can be done using Vitamin C indicator kits.
– Other similar experiments can be conducted. For
example, we investigate how storage conditions affect
the concentration of vitamin C in vegetables.
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What have we learnt
• Analyse raw data and how to present it
in a scientific manner.
• Search for information and compile
selected information together.
• Scientist mindset, never give up, if fail,
try again.
• Work together as a team.
• Ask questions.
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Acknowledgements
1.
2.
3.
4.
Miss Kong Ching Ying
Ms. Melanie Wong (Republic Polytechnic Supervisor)
Ms. Junainah Badron (Republic Polytechnic Supervisor)
Gan Eng Seng School Laboratory Technicians
References
1.http://en.wikipedia.org/wiki/Vitamin_C
2.http://www.nlm.nih.gov/medlineplus/ency/article/002404.htm
3.http://www.lenntech.com/fruit-vegetable-vitamin-content.htm
4.http://en.wikipedia.org/wiki/Capsicum
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Iodometric Titration
• Titration: Titration is a commonly used technique in
Chemistry to determine the concentration of a chemical
(titrant) by adding a measured volume of another
chemical (titrating solution) with a known concentration
until the formation of a coloured complex. The
concentration of the titrant can be then be calculated
using stoichiometry based on the volume of titrating
solution added.
• Iodine titration: The titrant in this experiment is ascorbic
acid and the titrating solution is iodine solution. Starch
indicator solution is also added into the titrant. The two
solutions react according to the following equation:
Ascorbic acid + I2  2I- + dehydroascorbic acid
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