Vitamin C: Which contains more, citrus fruits or green vegetables? Does it decompose over time?

Project Purpose

The purpose of this experiment is twofold. First, to detect and compare the concentration of vitamin C in several citrus fruit and green vegetable juices by titration of the juice with a corn starch-iodine vitamin C indicator solution; and second, to study the effects of (1) heat, (2) freshness, and (3) sunlight on the concentration of vitamin C in them.

School Name: Monzano Day School

Grade: Fourth

Teacher: Heather Behling

How did I get interested in the project?

1. A few years ago, I thought the "C" in vitamin C stood for the word "citrus" because television commercials related vitamin C to citrus fruit juices, for example, orange juice. In recent years, I started thinking that the "C" in vitamin C actually stood for the word "cold" because my mom generally asks me to take a vitamin C tablet everyday when I catch a cold. She knows very well that fruit juices do not exist in my list of favorites. Vitamin C tablets are not my favorites either, so I would like to scientifically investigate what else I can eat/drink to substitute these tablets or citrus fruit juices.
2. In 1994, Dr. Linus Pauling, the late American scientist, two time Nobel prize winner, and humanitarian, claimed, "vitamin C has the potential to prevent and treat common cold, flus, and cancer, all of which plague our society." This created a lot of interest in me to learn more about the topic.
3. I like science, especially chemistry is fascinating to me because in many experiments one can see changes in colors taking place due to chemical reactions.
4. A science experiment book suggested that a corn starch-iodine solution, which is royal blue in color when properly prepared, could be used to detect vitamin C in food juices, and I thought I would investigate it myself.
5. This is a fun project for me and my entire family.

The Scientific Hypotheses I would test:

Hypothesis II: Vitamin C decomposes over time, on exposure to sunlight, and heat.

The Scientific Background

For our body and mind to stay healthy, we need to eat a balanced diet, which should include the four food groups, vitamins and minerals. The four food groups include the milk group, fruits and vegetables, meat group, and breads and cereals. The vitamins include A, B₁, B₂, B₁₂, C, D, E, and K. The minerals include calcium, iodine, iron, phosphorous, potassium, and sodium.

There are three controlling variables in this experiment. First, the correct preparation of corn starch-iodine vitamin C indicator solution, and since this solution is unstable, it is freshly prepared each time it is used. Second, the amount of corn starch-iodine vitamin C indicator solution used for each test sample did not vary during the experiment. And finally, I made a control sample of Vitamin C tablet solution to determine whether a weaker or stronger concentration of vitamin C was present in each fruit and vegetable juice tested.

Glossary of Terms Used

What materials did I use?

1. 40 clear plastic cups
2. 40 plastic stirrers
3. 1 medicine dropper
4. food processor
5. large wire strainer
6. hot plate
7. cooking pot
8. one 250 ml measuring cup
9. two small bowls
10. one gallon of distilled water
11. starch-iodine vitamin C indicator
12. two teaspoons of corn starch
13. tincture of iodine
14. Juices (some prepared and some ready made) of several citrus fruits and green vegetables
15. one 100 mg vitamin C tablet

What did I do?

1. Prepared the juices that were not ready made and stored them in the refrigerator in cups.
2. Prepared a vitamin C standard. Placed a 100 mg vitamin C tablet in a small plastic bag and crushed it with a hammer into a powder. Added the powdered vitamin C into 100 ml of distilled water and mixed them well. This solution was then poured into a closed container and stored in the refrigerator.
3. Prepared the corn starch-iodine vitamin C indicator solution. Poured half a teaspoon of corn starch into the cooking pot. Poured a cup of distilled water into the pot. Heated and stirred the pot of water and corn starch solution until all the cornstarch is dissolved in the water. After heating, I let everything cool. Poured two teaspoons of the solution and one cup of distilled water into one of the cups. Using the medicine dropper, added four drops of tincture of iodine into the solution. The color of the resulting solution was royal blue. At that point, the corn starch-iodine test solution was done.
4. Titration of the vitamin C standard and the fruit and vegetable juices one at a time. The procedure for the titration was carried out using the following steps. Step 1: placed 25 ml of the corn starch-iodine indicator solution into a clear plastic cup. Step 2: used the medicine dropper to drop in the vitamin C standard or the juice of fruit or vegetable being tested. Step 3: after each drop, I stirred the resulting solution. Step 4: when the royal blue indicator changed to clear, I stopped adding the juice. Step 5: recorded the number of drops needed to change the royal blue indicator to clear. Step 6: repeated steps 1-5 above for each item being tested.
5. Poured a small amount of the vitamin C standard or the juice of each item being tested into two clear plastic cups. Placed one of the cups on a table under shade for one hour. Placed the other cup on a table under direct sunlight for one hour. Titration of the content of each cup was performed and the result recorded.
6. Heated one cup of each item being tested, one at a time, to boiling and let it boil for about 10 minutes. Let the item to cool down, and performed the titration procedure and recorded the results.

What happened?

The results obtained from the experiment performed above are recorded in the table below. These results are captured and analyzed through the four bar charts presented below.

Interpreting the Data Obtained

Heated one cup of each item being tested, one at a time, to boiling and let it boil for about 10 minutes. Let the item to cool down, and performed the titration procedure. No amount of juice affected the royal blue corn starch-iodine solution. Heat had completely destroyed the vitamin C concentration in all the items that were tested.

What did I learn?

1. The royal blue colored corn starch-iodine solution does work as a vitamin C indicator as suggested by the science experiment book.
2. Orange and lemon are high in vitamin C concentration amongst the citrus fruits tested in this experiment.
3. New Mexico green and red chili and green pepper are high in vitamin C concentration amongst the green vegetables tested in this experiment.
4. This research experiment proved both my hypotheses to be true. The first hypothesis is true because green pepper, New Mexico green and red chili, parsley, collard green and mustard green had higher concentrations of vitamin C in them compared to orange, lemon and other citrus fruits tested. The second hypothesis is true because we observed that the concentration of vitamin C in the items tested either stayed the same or dropped in the samples that were exposed to air, and sunlight for an hour.
5. Vitamin C is unstable because it decomposed when exposed to the air. The rate (speed) of decomposition varied between the fruits and vegetables tested.
6. Vitamin C is unstable because it decomposed when exposed to sunlight. The rate (speed) of decomposition varied between the fruits and vegetables tested.
7. Heat (boiling for about ten minutes) had completely destroyed the vitamin C concentration in all the items that were tested.
8. In the future, it will be interesting to investigate the loss of vitamin C from vegetables which have been cooked by various methods (various temperature settings).
9. Fresher the fruits and vegetables, higher the concentration of vitamin C in them. Eating fresh fruits and vegetable salads will provide a lot of vitamin C to one who catches a cold.
10. New Mexico chilis are healthy, tasty, and provide a lot of vitamin C in our diet.
11. Based on the claim of late Dr. Linus Pauling in 1994 and the results obtained from our experiment, people of New Mexico should have less heart diseases and cancers compared to the rest of the nation because we New Mexicans love to eat our state grown green and red chilis.
12. Chemistry is a lot of fun!

Where did I gather the background information from?