Ascorbic acid is commonly known as the vitamin C. The compound has a five-membraned unsaturated lactone ring with two hydroxyl groups attached to the doubly bonded carbons. Vitamin C is required for the formation of intercellular material. It is present in most of the fruits and vegetables. Deficiency of vitamin C leads to scurvy in human.
Vitamin C is powerful reducing agent which can reduce DCPIP (2,6-dichlorophenolindophenol) and changes the colour of DCPIP solution from blue to almost colourless. The more vitamin C, the more DCPIP can be decolourized.
What is the ascorbic acid content in fruit and vegetable fruits?
type of the solution (the juice)- each trial was carried out by using different solutions intended to decolourise DCPIP solution. All solutions were prepared either by squeezing the juice out of fruits and vegetables or by filtering the juice from the carton. Obtained juices were clear and transparent.
volume of the solution (needed for decolourisation) -certain volume of DCPIP is decolourised by a certain volume of ascorbic acid. Each sample of solution has different concentration of vitamin C therefore the volumes of solution needed for decolourisation of 1 cm3 of DCPIP would differ.
1) Concentration of DCPIP- the solution of DCPIP was prepared in larger amounts and the same sample was used in each trial. No changes were made to the content of the solution.
2) Volume of DCPIP used- in each trial one constant volume of DCPIP was used so as to obtain reasonable final values. The established volume of DCPIP was 1 cm3 and it was controlled by using the same pipette (1cm3 ï¿½0.05) to measure needed volume of DCPIP.
3) Type of equipment- each measurement was carried out using the same apparatus. Example: the DCPIP solution was measured using only one same pipette throughout the experiment
4) State of the decolourisation- as the experiment bases visual aspects, one sample of decolourised DCPIP was used as the basic one and later on each test tube (containing DCPIP and certain amount of juice) was compared with the basic one. The state (the colour) of decolourisation was supposed to be the same in both samples.
* 5 test tubes (20cm3 each 0.5cm3)
* 2 pipettes (10cm3 0.5)
* Pipette (1cm3 0.05)
* DCPIP solution
* Ascorbic acid solution (concentration 0.1%, 500cm3 1)
* Bottle of distilled water
* 8 filters
* Fruit press
1. Label the test tubes, then slowly pipette 1 cm3 of DCPIP into each test tube.
2. Take 5 cm3 of 0.1% ascorbic acid using the pipette.
3. Add the o.1% ascorbic acid drop by drop into the first test tube, gently shake the tube after each drop is added. As soon as the DCPIP becomes decolourised, note the number of drops added.
4. Wash the pipette and the beaker.
5. Into second test tube, add the same volume of distilled water as ascorbic acid that you added in test tube1. Gently shake the test tube and note your observations.
6. All solutions are tested 3 times.
7. Add the first sample of solution drop by drop, gently shake the tube after each drop is added and note the number of drops in order to decolourise DCPIP.
8. Continue in the same way with all solutions.
DCPIP is corrosive and toxic. Wash any spills with plenty of water.
The concentration of vitamin C in the samples was calculated using the equation drops of vitamin C needed to decolourise DCPIP times concentration of ascorbic acid solution (0.1%) divided by the number of drops of the sample solution needed to decolourise DCPIP.
Table4: The vitamin C concentration in samples.
Type of the solution
Vitamin C concentration [%]
Graph1: The graph showing the concentration of vitamin C [ %] in solutions used.
The samples (juices) used in the experiment were chosen using “the highest vitamin C content”i list. Also, to check whether or not the maturity state has influence on the change of vitamin C concentration, the newly bought and old lemon were used. To create wider range of solutions to compare both the juice from the fruit/vegetable and the fruit/vegetable juice from carton were used. Water was used as the control sample to illustrate that only a substance containing vitamin C could decolourise DCPIP.
The results obtained in the experiment are similar to the literatureii results and therefore are considered reasonable.
The lowest volume of the solution used was ascorbic acid (0.55 cm3), which means that among solutions used it has the highest concentration of vitamin C (0.1%).
Second highest vitamin C concentration has Rutinoscorbin and new lemon -0.057%.
The lowest vitamin C concentration has tomato juice from carton- 0.009%.
To put those results from the highest to the lowest vitamin C concentration:
I. Ascorbic acid
II. Rutinoscorbin and new lemon juice
III. Orange juice from carton
IV. Old lemon juice
V. Orange juice
VI. Tomato juice
VII. Tomato juice from carton
The results present that our everyday nutrition should include as much of the solutions above as to reach the daily need for the ascorbic acidiii.
In the experiment, some errors and mistakes occurred:
* Maturity state- vitamin C concentration decreases during the ripening process. Immature fruit has the highest levels because at a immature state citrus fruits contain more ascorbic acid hence the sour taste of un-ripened citrus fruits. There was no information which provided the state of the ripening process of the fruits/vegetables, therefore the concentration of ascorbic acid can vary (and differences in results and literature might occur). It is difficult to improve that aspect but some ECO shops sell fruits with additional information about their state.
* Human error- as the experiment considers only visual aspects, the human error could occur. Eye might have not notice a drop of solution added to DCPIP, two drops could bind and look like they’re one etc. To increase the reliability of this method and experiment, I suggest to use two people to watch and count the drops of solution added. Also the state of decolourization is not precise as, again, the human eye can be deceiving.
* Uncertainty of the equipment had small influence on the final results. The pipettes used to measure DCPIP volume could have slightly different scales- therefore one pipette should be used for DCPIP volume measure.