The effects of boiling and freezing on the Vitamin C
concentration in spinach
F.J. Smolders & C.K. Jansen
Gymnasium Felisenum, The Netherlands
Summary
Vegetables are edible parts of plants and are usually eaten as main meals and snacks. They contain many things necessary for a healthy diet and must be eaten many times a week. One of the healthiest vegetables around is spinach. Spinach contains Vitamins A, C and K, minerals like calcium and magnesium, fibers, folic acid and β-Carotene. Spinach helps
preventing cardiovascular diseases, strokes, overweight, cancer and osteoporosis. It is said that a vegetable is healthier when its fresh. Many people boil their vegetables before eating them, a process that destroys a lot of Vitamin C. If you want to preserve your food, freezing is a commonly used method. This could however, effect the Vitamin-C concentration. We wanted to test this. We took some fresh spinach and divided it into three groups. The first group was left untouched, the second group was boiled and the third group was frozen. We then measured the amount of Vitamin C in these three groups by titrating with 2,6-dichlorophenolindophenol. We think both boiling and freezing will lower the Vitamin C-concentration and we also expect to see a bigger decrease through boiling because the high temperature will destroy the Vitamin C.
Introduction
Spinach (Spinacia oleracea) is a flowering
plant in the family of Amaranthaceae. It is
native to central and south-western Asia. It
is an annual plant (rarely biennial), which
grows to a height of up to 30 cm. Spinach
may survive over winter in temperate
regions. The leaves are alternate, simple,
ovate to triangular-based, very variable in
size from about 2-30 cm long and 1-15 cm
broad, with larger leaves at the base of the
plant and small leaves higher on the
flowering stem. The flowers are
inconspicuous, yellow-green, 3-4 mm
diameter, maturing into a small hard dry
lumpy fruit cluster 5-10 mm across
containing several seeds.
Vitamin C or ascorbic acid is an essential
nutrient for humans and many animals. Figure 1: Spinach
The pharmacophore of vitamin C is the
ascorbate ion.
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In living organisms, ascorbate is an anti-This method was repeated three times for oxidant, since it protects the body against the 75g of spinach that was left. oxidative stress, and is a cofactor in several A burette was filled with DCPIP and the vital enzymatic reactions. four residues were titrated. Because DCPIP
Vitamin C react 1:1, the amount mol and2,6-dichlorophenolindophenol or DCPIP DCPIP used to titrate the residue is equal is a blue chemical compound used as a to the amount mol Vitamin C in the residue. redox dye. Oxidized DCPIP is blue, reduced DCPIP is colorless. 2.
Some fresh spinach was put in a freezer DCPIP and Vitamin C react 1:1, so when,
until it was completely frozen. after titration, one mol of DCPIP was
The exact same method as described in test needed to turn the Vitamin C solution red,
was then used to determine the amount of one mol of Vitamin C was in the solution.
Vitamin C in the residue.
This method will be used to measure the
amount of Vitamin C in our three groups 3.
of spinach. Once again 100g of spinach was weighted
and divided it into 4 portions of 25g. One Our research question is: how big is the portion of 25g. was put in a volumetric effect of boiling and freezing on the flask and some water was added. The Vitamin C concentration of spinach? water + spinach was then boiled for 15
minutes and filtered it when it was done. Out hypothesis is that both processes will
This was repeated three times for the 75g have a big effect on the Vitamin C
that was left. The method as described in concentration, boiling having the largest
test 1. was then repeated again by grinding, effect.
filtering and then titrating the spinach. Experimental Design
The experiment was split up into three There also were a few variables we needed parts: to take into account:
1. Normal Spinach
2. Frozen Spinach Independent Variable: The state the
3. Boiled Spinach spinach was in (normal, boiled, frozen) 1.
100g of spinach was weighted and divided Dependant Variable: The amount of
it into 4 x 25g. DCPIP needed for titration. One portion of 25g was then put into a
mortar and some sand and 25ml of acetic Control Variables: Type of spinach,
acid was added. These materials were boiling time, amount of water used for grinded until nothing but fluid was left. boiling, room temperature, amount of The fluid was filtered using some filter acetic acid added, amount of sand added, paper and a funnel. 10ml of the residue filtrating time, filtrating paper. was taken apart and the rest was thrown
away.
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Figure 2: A visualization of our experiment
Results
The tables below show the amount of ml
DCPIP needed for titration:
DCPIP Boiled Spinach DCPIP Normal Spinach
Titration (1ml) - Test Titration (1ml) 0.4ml
Titration 1 (10ml) 0.7ml Titration 1 (10ml) 4.05ml
Titration 2 (10ml) 0.5ml Titration 2 (10ml) 4.90ml
Titration 3 (10ml) 0.8ml Titration 3 (10ml) 4.55ml
Titration 4 (10ml) 0.7ml Titration 4 (10ml) 3.95ml
Type of spinach Average DCPIP DCPIP Frozen Spinach
Test Titration (1ml) 0.2ml Normal 4.36ml Titration 1 (10ml) 0.5ml
Frozen 0.825ml Titration 2 (10ml) 1.00ml
Titration 3 (10ml) 1.10ml Boiled 0.675ml Titration 4 (10ml) 0.70ml
3
6
5
4
Titration 1
3Titration 2
Titration 32
Titration 4
1
0
Normal spinachFrozen spinachBoiled spinach
Figure 3: A graph of our results (DCPIP)
Mg Vitamin C in spinach
Our DCPIP had a concentration of 9,14e-4
or 0.000914 mol/liter and Vitamin C has a
molecular mass of 176.13g
We can calculate the amount of mg
Vitamin C using:
(ml DCPIP) x 0.000914 x 176.13 = mg
Vitamin C
Vitamin C DCPIP Normal Spinach Boiled Spinach
Test Titration) 0.064mg Titration -
Titration 1 0.65mg Titration 1 0.11mg Titration 2 0.79mg Titration 2 0.08mg Titration 3 0.73mg Titration 3 0.13mg Titration 4 0.64mg Titration 4 0.11mg
Type of spinach Vitamin C Average Vitamin C Frozen Spinach
Test Titration 0.032mg Normal 0.70mg Titration 1 0.080mg
Titration 2 0.16mg Frozen 0.13mg Titration 3 0.18mg
Boiled 0.11mg Titration 4 0.11mg
4
Mg Vitamin C
0,8
0,7
0,6
0,5
Normal Spinach
0,4Frozen Spinach
Boiled Spinach0,3Mg Vitamin C
0,2
0,1
0
State of Spinach
Figure 4: A graph of our results (Average Vitamin C)
As you can see in the tables and the graphs
our results seem to be pretty accurate. The
measurements are pretty close together and no mistakes seem to have been made
(otherwise one of the results would’ve been way off).
As you can see the boiled and frozen
spinach contain much less Vitamin C then the normal (fresh) spinach.
The difference between boiled and frozen
spinach seems to be rather small Since no weird measurements showed up,
and because these results add to our hypothesis, we can conclude that these results are reliable.
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Evaluation Discussion and conclusion The experiment was fun to perform. The There definitely is a difference in the method used to determine the amount of Vitamin C concentration after boiling and Vitamin C was easy to use. The freezing. Boiling seems to have the biggest experiment was performed step by step and impact. There is a difference of 3,685 ml no grove mistakes were made. The DCPIP/0.59mg Vitamin C. After freezing experiment could however be improved. the difference is 3,535 ml DCPIP/0.57mg
Vitamin C. For example, more portions of spinach
could have been used. Also, the titration
The answer to our research question ‘how could/should have been a little bit more
big is the effect of boiling and freezing on precise. The tap on our burette was a bit
the Vitamin C concentration of spinach?’ hard to operate, so we may have added too is that the effect is pretty big. If you look at much DCPIP. That way, our results the results you can see that there is a huge would’ve been a bit more reliable. We also difference in Vitamin C, approximately 6/7 didn’t have enough time to finish all our
of the original Vitamin C has disappeared. planned tests. Originally we wanted to buy
We can conclude that boiling and freezing some frozen spinach and see if Vitamin C
has a big impact on the Vitamin C was added manually to counter the effect
concentration of spinach and it’s healthier of freezing. Perhaps we could do this to eat spinach fresh. another time.
Bibliography
www.wikipedia.com
www.bioplek.org
Cito Arnhem 1999 - Bepaling van het
gehalte vitamine C in Spa Citroen
RIS-practica - Bepaling van het gehalte
aan vitamine C
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