Defeating Oxidation in
Apples
By: Alexa Conzuelo
Per. 6 Mr. Leingang
Question
• Which acidic fruit juices with
different levels of pH best
prevent an apple slice from
becoming oxidized?
Hypothesis
As I squeeze different acidic fruit juices then the
lemon juice will best prevent the apple slice from
becoming oxidized because it has the lowest pH
level of all the fruits and the lower the pH the
better it prevents oxidation in fruit. Also I believe
that the orange juice will least prevent oxidation
because it is the sweetest of all the fruit so it has a
higher level of pH.
Background Information
Oxidation is when two materials come into contact with each other and an electron is lost. This is
both good and bad because it can cause things to rust such as metals. It can also make aluminum
more durable, so its not such a bad thing. Oxidation does not weaken metal or copper when it rusts
but it creates a patina, which is a film that develops on a material over a long period of time. This
also affects fruits.
There are some negative affects if something becomes oxidized. On a car the paint becomes dull
over the years. A layer of wax protects the car and paint from oxidation. A bicycle left in the rain
becomes rusty and unusable. Also a greenish coat settles on copper that has become oxidized over
the years. Some metals don’t become oxidized because the steel is covered with a layer of metal that
doesn’t cause a chemical reaction with oxygen. Fruits and vegetables turn brown and blemish,
causing them to look inedible.
Oxidation affects fruit and causes blemishes, or browning. This happens because when fruit is cut
it comes into contact with oxygen. Then enzymes contained in the apple make a chemical reaction
with the oxygen. This is what makes the fruit darken. Even if the vegetable or fruit is brown it is still
edible, although it is best to cut those parts off.
There are ways to prevent vegetables and fruit from becoming oxidized. One way is to cover the
food item in plastic wrap. This prevents the cells and enzymes to interact with oxygen. Also you can
slightly heat the fruit, which causes the destruction of the enzymes. Another method, which is the
one I used, is to add citric acid to exposed parts of the fruit. This prevents oxidation because the
juices have a very low pH and it interferes with the 3D structure of the enzymes. So it disrupts the
structure, and prevents it from functioning.
Now you may be thinking what pH is. Basically it’s the measure of a liquid’s acidity or basicity. You
can measure this by using a pH indicator, which changes color to see the number of pH. The
measure of pH isn’t absolute though, but close enough. Most values will range from zero to
fourteen. Pure water at a lukewarm temperature is near seven, which is neutral. Less than seven is
considered acidic, and more than seven is alkaline. An example is lime juice, which has a pH of two to
2.8, so its acidic. Baking powder is around 8.2. pH is important for food science, medicine, biology,
chemistry, and other things.
Variables
• Manipulated variable: the different type of acidic fruit juice squeezed onto
the apple slice
• Responding variable: the amount of browning on the apple slice that is
recorded
• Controlled Variable: Type of apple, amount of juice squeezed onto apple,
size of apple slice, amount of time apples are left to brown
Materials
•
•
•
•
•
•
•
•
Two Fuji apples
One lemon
one lime
one orange
One grapefruit
Stopwatch
Knife
Cutting board
Procedures
• 1. Cut four slices of apples around the same size and thickness, like in the
diagram. Be careful when using the knife.
• 2. Cut a lemon in half and squeeze a tsp of juice.
• 3.Pour it on one side of apple slice # 1
• 4. Squeeze another tsp of juice and it on the other side.
• 5. Repeat steps 2-4 for the lime juice for slice # 2, orange juice for slice # 3
and grapefruit juice for slice # 4.
• 6. Put the apple slices on a plate.
• 7. Wait for two hours. Make sure the slices are not in the path of sunlight
and at room temperature.
• 8. Record your observations.
• 9. Repeat steps 1-8 for one more trial.
Data table Trial 1
Juices
Observations of browning on apples
Lime juice
Some browning on the top and
bottom of apple slice.
Lime juice
Very little browning on back, blemsih
on the bank.
Orange juice
Some browning over all of the apple
Grapefruit juice
Browning all over the apple, more on
the top front side.
Diagram
Data continued Trial 2
Juices
Observations of browning on
apples
Lemon juice
Slight amount of oxidation on
front, little bit more on the back
Lime juice
Left part in the front large
blemish, very little on back
Orange juice
Brown on back and front
Grapefruit juice
Slight oxidation on the front and
back of apple slice
Diagram
Conclusion
I believed that the lemon juice would best prevent
an apple lice from becoming oxidized, and the orange
juice the worst. My hypothesis was correct because
on both trials the apple slice covered in lemon had the
least oxidation. The orange juice covered apple slice
had the highest oxidation amount on both trials. The
difference was that apple slice number one looked
edible, while the apple slice number three didn’t.
Therefore if I repeat my experiment the visible
amount of oxidation on the lemon juice covered apple
slice should not increase, and the orange juice
covered slice should still have the most oxidation.
Abstract
The purpose of my project was to see which acidic
fruit juice best prevented an apple slice from
becoming oxidized. I thought that the lemon juice
would best prevent oxidation. To my knowledge there
was no inconsistency in my experiment that could
have affected my data. Upon completing my project I
learned that both lemon and lime juice both work well
against oxidation. Also orange juice isn’t very good as
an anti-oxidative because its too sweet. There are
some things I could have done differently and one of
them was I could have left the apples exposed to air
longer to see the fuller extent of how well the juices
prevented oxidation.