Will Sunlight Affect the Amount of Vitamin C in Orange Juice?

	Project title: Will Sunlight Affect the Amount of Vitamin C in Orange Juice?
Difficulty level:	Middle school
Main link:	None

Hypothesis:

I thought that if 18 270-mL cups of orange juice were left for different amounts of time in a constantly sunny area, the amount of ascorbic acid (vitamin C) would be affected in the orange juice more as the time wore on.

Materials:

540 mL 100% Tropicana original orange juice
18 270-mL plastic cups
2 droppers (with measurements up to 5 mL)
2 32 cm x 22 cm x 6 cm trays
(as needed) Safeway Select iodine
180 drops cornstarch solution (80 mL cup
cornstarch, 400 mL water)
(as needed) toothpicks
1 7 ½ mL measuring spoon
1 shaded area
1 constantly sunny area
1 permanent marker
1 large piece of cardboard
1 thermometer
(as needed) Sam’s choice plastic stretchable wrap

The Procedure:

1. To begin, I filled 18 270-mL cups to 30 mL of orange juice with a 7-½ mL measurement spoon, and took care that each spoonful was even and exact. I did it in a shaded area with very minimal sunlight as to not affect the outcome of the experiment.
2. Next, with a permanent marker, I marked 6 cups as 1, 6 as 2, and 6 as 3 on the sides.
3. Placing each in 2 different trays (one for the cups in the sunlight and one for the cups in the shade), I brought them outside.
4. The 9 in the sunlight were lined up along the step, close enough that the rims were touching.
5. The 9 in the shade were put in 3 lines behind a large piece of cardboard (once again touching) and I made sure that all 18 cups were within 90 cm of each other to ensure their identicalness. Throughout the experiment, the cups were constantly watched.
6. I took the temperature of the start of the experiment (12:23 pm, December 30, 2005), using a thermometer approximately 450 cm away from the cups. Every ten minutes, I took the temperature and recorded it in my notes for an average of the entire experiment.
7. At 1:23 pm, I quickly placed the number 1 cups into one of the trays used before and rapidly brought them inside into the shaded area.
8. I determined the amount of ascorbic acid (vitamin C) in each of the cups of orange juice using these steps (first covering work area with plastic wrap):
a. With 1 dropper, I added 10 drops of the starch solution (80 mL cup corn starch, 400 mL water) to 1 cup. Then I stirred the cup’s contents with a toothpick until I was sure the starch had all dissolved.
b. I began adding the iodine to 1 of the cups 1 drop at a time, and made sure to count the number of drops I was adding. Then I stirred the solution after the addition of each drop (with a different toothpick than the one used for the starch solution).
c. As I kept adding drops, I watched the solution carefully until it began to change color. When the solution first changed color, I stirred for at least 20 seconds. If the original color came back, I added more iodine. If it didn’t, that meant I had reached the endpoint.
This process is called titration.
9. I did step 8 with all of the number 1 cups, recording each amount and whether the cup was in the sunlight or not in my notes.
10. At 2:23 pm, I repeated step 8 and 9 with the number 2 cups.
11. At 3:23 pm, I repeated step 8 and 9 with the number 3 cups.

Results:

There was no major difference in the amount of ascorbic acid (vitamin C) in the cups that were in the sunlight as opposed to the controls over 3 hours. The drops needed to reach the endpoint were within 5 drops (with one outlier) regardless if they were in the sunlight or not. When I brought the cups inside, I noticed only one difference among them: the lit ones had lighter colored orange juice than the controls. Otherwise, including the amount of ascorbic acid, they appeared to be exactly the same, as you can see by the charts below.

Number 1 cups with an average temperature of 51.14° F
Group (Lit, Shaded) Cup Drops Needed To Reach Endpoint
1 L 1 19
1 L 2 20
1 L 3 20
1 S 1 17
1 S 2 20
1 S 3 18

Number 2 cups with an average temperature of 52. 85° F
Group (Lit, Shaded) Cup Drops Needed To Reach Endpoint
2 L 1 18
2 L 2 18
2 L 3 19
2 S 1 25
2 S 2 20
2 S 3 21

Number 3 cups with an average temperature of 52.16° F
Group (Lit, Shaded) Cup Drops Needed To Reach Endpoint
3 L 1 20
3 L 2 19
3 L 3 19
3 S 1 22
3 S 2 20
3 S 3 21
Conclusion:
I was surprised that my hypothesis turned out to be incorrect. The reason I thought that the orange juice’s ascorbic acid content would be changed was based on the fact that ascorbic acid is an antioxidant. When met with sunlight, I thought it would be oxidized (or destroyed, whatever you prefer) by the sunlight to protect the other vitamins and content of the orange juice. I read that light and heat would damage the acid, and that after 1 hour, 30% of it would be gone from the juice. I really was curious, and so, in the same place as the others, I placed just one cup to test if it would change over a longer period of time. It did! It took only 11 drops to reach the endpoint. I was excited, and wanted to test it like that to make my experiment better. Unfortunately, on the one day I could have done it, the weather turned against me. It was very foggy, and it began to snow. Still, I did achieve in this experiment what I wanted to – I wanted to find out if the content of ascorbic acid would be changed more over 3 hours, and it didn’t. Perhaps later I can do this experiment again.