Yang 1
Jeffery Yang
Dr. Cousins
PRISM
Differences of Vitamin C in Oranges When Exposed to Sunlight
Abstract
This study shows the loss of Vitamin C (ascorbic acid) in whole oranges after seven days
of sunlight exposure. The study is based off a review that Steven Nagy wrote in 1980 about the
lost of Vitamin C in citrus fruits. About fifteen to twenty oranges were picked out and set on top
of a greenhouse rooftop located in San Bernardino, CA for a week and titrated (3 individually)
each day as it was exposed to sunlight. After collecting the data, a line graph was plotted and it
showed that the Vitamin C content was lost during the first couple days (1-3) of exposure.
Instead of a continuing degradation, the Vitamin C content appear to rise, possibly because of
other compounds or enzymes that oranges contain have reacted with the iodine solution after
certain aging or temperature is reached. The findings of this study open up a new topic of study
to examine what caused the sudden apparent rise of Vitamin C content in whole oranges after
sunlight exposure.
Purpose
To find how much vitamin C remains in oranges following a week of exposure to
sunlight.
Introduction
Oranges are citrus fruits that are grown and known all over the world for their vitamin C
content. Vitamin C, also known as ascorbic acid, is one of many kinds of vitamins consumed
from eating citrus fruits. In addition, Vitamin C has health benefits because it can prevent health
Yang 2
problems such as scurvy. Scurvy is disease that leaves a human body in “state of dietary
deficiency of vitamin C” (Goebel). According to the US Food and Drug Administration (FDA),
it is recommended for women to intake 75 mg of vitamin C per day and for men to take 90 mg of
vitamin C.
To determine the amount of vitamin C in oranges, an oxidation-reduction reaction can be
performed. Vitamin C reacts with iodine solution with little interference, in freshly squeezed
juice. Performing an acid-base titration will determine the amount of vitamin C. Iodine solution
is the oxidizing agent and vitamin C is a reducing agent (reaction 2). In order to form iodine
solution, potassium iodate (KIO3) and potassium iodide (KI) are combined in an acidic solution
(reaction 1):
2 IO3- + 10 I- + 12 H+ --> 6 I2 + 6 H2O (reaction 1)
C6H8O6 + I2  C6H6O6 + 2I- + 2H+ (reaction 2)
Ascorbic Acid
Dehydroascoric acid
When starch solution is added as an indicator, the endpoint of the reaction occurs after all
the vitamin C has been consumed. The blue-black color appears because of the iodine and starch
indicator reacting with each other, when there is excess iodine, meaning that the endpoint is
reached.
Procedures/Methods
Oranges
About 15-20 oranges were set on a greenhouse rooftop to be exposed to sunlight on July
20, 2011 in San Bernardino, CA. Three oranges per day were hand juiced, then titrated
individually (3 replications each) and recorded. Oranges were titrated on Day 0 (before sunlight
exposure), Day 1 were titrated after one day of sunlight exposure, and continued the same
process until Day 7 (oranges exposed to sunlight for seven. days).
Yang 3
Preparation of iodine solution
Five (5.00) g potassium iodide (KI), 0.270 g potassium iodate (KIO3), and 30 mL 3 M
sulfuric acid were added in a 500 mL volumetric flask. Two hundred (200) mL of distilled water
was added, and the solution was mixed well and diluted to 500 mL.
Preparation of Vitamin C solution
One-tenth of a gram, 0.1000 g of Ascorbic Acid (AA) was added into a 100 mL
volumetric flask, mixed well with 50 mL distilled water, and then diluted to 100 mL.
Standardizing the iodine solution
A 25 mL aliquot of Vitamin C solution was transferred into a 250 mL Erlenmeyer flask
using a 25 mL volumetric pipette with a 25 mL pipette pump. Thirty (30) drops of 1% starch
indicator (or 2% starch indicator used 15 drops) were added to the 250 mL Erlenmeyer that
contained the juice. A buret was rinsed twice with 5-10 mL of iodine solution. The iodine
solution was titrated with the standard Vitamin C until reached an endpoint (when the color
changes from clear to blue/purple). The final volume was recorded to the nearest 0.1 mL. The
process was repeated three times and data was performed with the Q-Test to remove any
different kind of data.
Titrating the orange juice samples
Each orange was measured for a total volume of juice by cutting the orange in half and
squeezing the fruit with a juicer appliance. The total volume of juice was measured using a
graduated cylinder and then recorded. An aliquot of 5, 10, 20, or 25 mL of juice (depending on
how much juice in total) was in a 250 mL Erlenmeyer flask using volumetric pipettes and 25 mL
pipette pump. The starch indicator (30 drops of 1% starch or 15 drops 2% starch) was added
along with the aliquot of juice. The orange juice sample was titrated until it reached endpoint
Yang 4
(when color changes from yellow-orange to blue-blackish). The final volume was recorded to the
nearest 0.1 mL. The process was performed at least three times for every orange titrated and all
data was tested with the Q-test for off data value.
Microsoft Excel was used to calculate the T- Test (two-tailed, paired) and to graph the data sets
from Day 0 to Day 7.
Data
Time
mg/100mL
(Concentration)
Total AA
T Test
(Day0 Total
AA)
64.5526
T Test
(Day0
mg/100mL)
-
-
Total
Volume of
Juice, mL
334
Day 0
57.86890653
Day 1
56.59764903
53.45612
Day 4
41.88322681
Day 5
Weather
80 F/58 F
0.829969
0.404616
284
78 F/57 F
35.05361
0.052648
0.042976
252
95 F/45 F
57.23327778
41.6781
0.239647
0.154905
242
96 F/60 F
Day 6
45.87399418
47.35653
0.237693
0.198571
310
94 F/63 F
Day 7
46.98146721
40.32506
0.077811
0.024142
265
90 F/61 F
0
0
0
0
0
0
0
0
0
0
0
0
Table of the comparison of the concentration and total AA of Day 0 to each of the individual days
The T test performed was a paired T test, meaning using two different sets of data to
compare, and given a probability of the data being the same. The probabilities seen in the table
are the sets of data compared to Day 0 data set representing the chances of the two sets of data
being similar.
Yang 5
Effects of Sunlight on Ascorbic Acid Content in Whole
Oranges
70
65
60
55
50
mg/100mL
45
Total AA
40
35
30
Day 0
Day 1
Day 4
Day 5
mg/100mL 57.8689 56.5976 41.8832 57.2333
Total AA
Day 6
Day 7
45.874
46.9815
64.5526 53.4561 35.0536 41.6781 47.3565 40.3251
Using oranges exposed to sunlight for different time periods, the different colored lines represent AA total and concentration
.
The graph shows the total amount of AA and mg of AA per 100 mL of juice dropped
steadily after 1-3 days of exposure to sunlight (average of data from three oranges). Instead of
further degradation, there was a surprising rise in apparent AA concentration after Day 4
exposure to sunlight.
Data Analysis
According to the data, the total amount of ascorbic acids, mg/100mL, and volume of
juices dropped steadily after 1-3 days exposed to sunlight. The value of the T Test performed on
each different day based on Day 0, are all significantly different on both the total amount of
ascorbic acid and mg/100mL (Data Table). In addition, the volume of juice from 1-3 day has
dropped depending on the size of the fruits picked. The weather temperature from Day 0 to Day
4 got hotter as each day went by, which means each orange would constantly be exposed to
higher temperature before analysis.
Yang 6
As the mg/100mL and total amount of AA are dropping from Day 0 to Day 4, Day 5-Day
7 had different outcomes. Instead of degradation, there was a rise in mg/100mL and apparent
amount of AA (refer to line graph). It was expected that because the temperature and time both
increased on Days 5-7, the AA content and juice volume would continue to decrease. In addition,
the volume of the juices on Day 6 (310 mL) has a higher amount of juices than Day 5 (242 mL),
and the apparent AA showed an increase for over Day 4. The likely cause of the increase was a
metabolic reaction produced during heating/arid conditions, such as ethylene, reacting with the
iodine making ascorbic acid concentration appears higher than they are.
Conclusion
Exposure to the sunlight (1-3 days) has degraded the ascorbic acid content, but after 3-4
days a climb in apparent ascorbic acid content occurs, probably from a side reaction of some sort
that occurs in an orange. Many compounds or enzymes could have reacted with the iodine
solution when juice aging orange are titrated or perhaps temperature can play a part where only
as certain conditions are reached, the side reaction can occur. This side reaction would open up a
new topic for further research for future ascorbic acid experiments. Iodine titration, while being
effective for Vitamin C in fresh oranges, is not as effective for stressed oranges due to side
reactions. Other methods to more explicitly examine AA content, such as HPLC analysis would
be better to study the aging.
Yang 7
References
Dr. J. Roger Bacon. “Determination of Vitamin C by an Iodometric Titration.” July 7, 2011
Goebel, Lynne, Bradley S. Buckler, Henry P. Driscoll, Dirk M. Elston, Anne E. Laumann, Julia
S. Minocha, Van Perry, Kathryn Schwarzenberger, and Janet J. Wong. "Scurvy."
Medscape. WebMD Health Professional Network. Web. 19 July 2011.
Nagy, Steven. "Vitamin C Contents of Citrus Fruit and Their Products: a Review." Journal of
Agricultural and Food Chemistry 28.1 (1980): 8-18. Print.
Acknowledgments

National Science Foundation (NSF) Grant # DMS-1035120

Dr. Rolland Trapp, Department of Mathematics, CSUSB, Head of PRISM

Dr. Kimberley R. Cousins, Department of Chemistry and Biochemistry, CSUSB, PRISM
Chemistry Mentor

Vannary Sann, Department of Chemistry and Biochemistry, PRISM Student Assistant

Department of Chemistry and Biochemistry, for their hospitality