Investigating the Browning of a Fruit or Vegetable
Aim: To design, carry out and report on an experiment which
investigates the browning of red delicious, pink lady, granny smith,
braeburn and royal gala apples with regard to temperature and pH
Hypothesis: It is expected that each apple will brown at a faster rate
at warmer temperatures and at an optimal pH level. The degree and
speed at which each apple portion browns will depend upon the strength
and amount of the enzyme phenolase present in each portion.
Background Information: Apples will turn brown when cut and exposed to
air. This can be partly attributed to the action of enzymes which are
organic catalysts. They speed up chemical reactions without taking
part in the reaction. Enzymes are sensitive to temperature and pH and
have optimal levels of each variable at which they will function at
the fastest rate.
For the browning reaction of an apple to occur, three conditions are
1. The enzyme know as phenolase must be present
2. The target/substrate of the phenolase called phenols must be
3. Oxygen must be present in the surrounding atmosphere.
Apple browning occurs close to the fruit's flesh surface. This is
because cells beneath the fruit's skin are damaged and exposed to
oxygen. In whole apples, the phenolase and phenols are kept separate.
However, when one cuts or bites into any type of apple, the cells are
opened and the enzyme and target are free to react with one another.
The phenolase proceeds to combine the phenols and oxygen into the
different chemical of polyphenol oxidase which is yellow/brown in
colour. This type of reaction is an oxidation reaction. The brown
colouring of polyphenol oxidase is what is seen on the apple surface.
Ã˜ Universal indicator
Ã˜ 4 small plates
Ã˜ Small bowl
Ã˜ 10 teaspoons of citric acid
Ã˜ Alkaline solution, 1t Jif quarter cup water
Ã˜ 6 royal gala apples
Ã˜ 6 red delicious apples
Ã˜ 6 granny smith apples
Ã˜ 6 braeburn apples
Ã˜ 6 pink lady apples
Ã˜ Apple corer
Ã˜ 1 teaspoon
1. Place a thermometer in the freezer with the bulb not touching any
frozen items, (this will create a false reading) for 5 minutes.
Record the result.
2. Proceed to test the temperatures of the fridge, a kitchen
cupboard and on an outdoor table exposed to the full sun. Record
3. Core 3 royal gala apples and slice them into quarters.
4. Sprinkle 1 teaspoon of citric acid on 3 of the apple quarters and
1 teaspoon of Alkaline Jif solution on a different 3 apple
quarters. Leave the remaining 4 quarters untouched.
5. Immediately place 1 acidic quarter, 1 alkaline quarter and 1