The effects of boiling and freezing on the Vitamin C
concentration in spinach
F.J. Smolders & C.K. Jansen
Gymnasium Felisenum, The Netherlands
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.
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
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
Figure 2: A visualization of our experiment
The tables below show the amount of ml
DCPIP needed for titration: