DELL CHAMPS CONTEST
AROOSA HODA
CLASS- VI-A
MOTHER MARY’S SCHOOL,
MAYUR VIHAR DELHI
110092
Why Do Apples Turn
Brown?
Have you ever bitten into an apple, set it down
for a few
moments, and found that it has turned brown?
This is caused by an enzyme (polyphenol oxidase and
Catechol oxidase are two common examples) that reacts
with oxygen in the air and an iron or copper cofactor in
the fruit.
A cofactor is a component that is necessary for
a certain enzymatic reactions to happen.
The fruit starts to oxidize, when electrons are lost to another
molecule (in this case the air), and the food turns brown. In
other words, it’s like edible rust on your food!
CONTINUED…….
Oxidation can be prevented or slowed down
by not allowing oxygen to get to the
surface of the fruit. To accomplish this,
you can cook the food, which destroys
the enzyme. It is also possible to prevent
browning without cooking by covering the
fruit (preventing air from reaching the
fruit), or by lowering the pH on the
surface, making it more acidic
Problem:
Which liquid do you think will prevent
the food from turning brown the best?
Why?
Materials
Baking sheet or wax paper
Labeling tape
Pen or marker
Tongs
Bowl
Knife
Lemon juice
Vinegar
Clear soda
Olive oil
Water
Saltwater
Potato
Apple
Banana
Avocado
Any other liquid you want to test
Any other fruit or vegetable you want to test
Camera (optional)
Procedure
1. Use the tape to create labels for each type of liquid
you will test.
2. Place your labels on the baking sheet or wax paper.
This is where you will set down your samples for
observation.
3. Cut each fruit or vegetable into slices at least 1-cm
thick. Make sure you have as many slices of each
food item as you do liquids to test, plus one more for
a control. Have an adult help you cut your samples!
4. Set out a slice of each food item on the baking sheet
or was paper under the heading “Control.”
Procedure--- Contd
5. Fill the bowl with enough liquid to fully submerge each
sample.
6. For each fruit or vegetable you are testing, dip a slice
into the liquid with tongs. Be sure to cover the whole
slice! Let the extra liquid drip off before placing it
under the correct label on the baking sheet or wax
paper.
7. Rinse out the bowl and repeat until you have made
samples with each liquid.
8. Record all your observations, taking note of the time.
You can also take pictures to document how the food
turns brown over several hours.
Results
Lemon juice, Vinegar, clear soda will all
prevent food from turning brown quickly.
These liquids are acidic, so they will lower
the pH of the food surface. Olive oil, will
also prevent food from browning, but is less
effective than the acids. Water and salt
water will also slow the browning of foods.
Lemon juice is the most effective, and by
chance, also the most delicious!
Why is it important to have a
control?
Having a control group is necessary
because it is important to know how
long the food samples will take to turn
brown without any liquid added.
Why should the food samples
be cut?
The food’s skin protects the inside “meat” of
the fruit or vegetable from damage and
debris.
When a fruit or vegetable is dropped and the
skin is poked or broken, the food often goes bad
faster. The reason fruits and some vegetables go
brown when they are cut is because the part
containing the oxygen-reactive enzyme is
exposed.
There is then a lot of surface area for the air to
come in contact with the food.
 For the most part, brown fruits and vegetables
still taste fine, they just do not look very
appetizing.
How do acids prevent browning?
Acids prevent browning because they react with
the oxygen that comes into contact with the
surface of the sample.
Once all the acid (or whatever else is covering
the surface) has reacted with the oxygen or the
acid has degraded or washed off, then the
sample will start to brown again.
Stronger acids, like lemon juice, can even
denature the enzyme.
This means that the enzyme can no longer
perform its original function because of its
environment.
APPLE WITH LEMON JUICE
APPLE WITHOUT LEMON JUICE