Gan Eng Seng School Presents
Apple Browning
Project
The effect of different PH levels on apple browning.
AIM
To determine the pH range that is
most effective in slowing down the
enzymatic browning of apples
HYPOTHESIS
•
pH level affects the rate of action of polyphenol
oxidase enzymes. The lower the pH of the
solution the apples are soaked in, the lower the
rate of enzymatic browning of the apples.
INTRODUCTION
Apples have a group of enzymes called
polyphenol oxidases.
When apples are cut, polyphenol oxidase
catalyses the reaction between polyphenols,
which are naturally present in apple tissues,
and oxygen.
This oxidation reaction leads to the formation
of black-brown complexes called melanin,
causing browning of apples
MATERIALS
•Measuring cylinders
•Beakers
•
Red apples
•Stirring Rod
•
Lime (pH 2.38)
•Tea spoon
•
Lemon (pH 2.49)
•Electronic balance
•
Distilled water (pH 7)
•Knife
•
Common salt
(sodium chloride) (pH
7)
•Chopping Board
•white paper
•Marker
METHOD
•
•
•
•
•
•
•
100ml of fresh lime juice, lemon juice, salt solution
and distilled water were prepared.
The apples were cut longitudinally into 5cm by 5cm
slices.
The exposed surface of the slices of apple were
immersed into the different solutions prepared.
Apple slices were removed from the solutions after 5
minutes.
The treated apple slices were placed on a piece of
white paper
The apple slices were labeled with the name of the
solution it was dipped in accordingly.
Photographs of the apples were taken at 1 hour
intervals for a total of 5 hours to show the colour
changes in the apples
Figure showing
a 5 cm x 5 cm
apple slice
DISCUSSION
Lime
Lime
Lime
DISCUSSION
As seen from the results, lime juice is able to preserve the
fresh-cut colour of the apple best, followed by lemon juice,
salt solution and lastly distilled water.
Though salt solution and distilled water have a pH value of 7,
salt solution is able to retain the colour better. Salt (sodium
chloride) is a water binding chemical which removes water
molecules from the cells. This causes dehydration of the
apple. Since water is an important factor for enzymatic
browning of apples, salt solution has an anti-browning effect.
DISCUSSION
• Effect Of Acids
1.Lemon and lime juice contains ascorbic acid
(vitamin C) and citric acid.
2.Ascorbic acid also acts as an anti-oxidant.
3.These acids react with oxygen before the oxygen
reacts with the polyphenol oxidase, thus, giving an
anti-browning effect.
DISCUSSION
• Effect of pH
1. Polyphenol oxidase (PPO), which is responsible for the
enzymatic browning of apples, works best when the pH
level is between 5.0 and 7.0.
2.By bringing the pH level to less than 3, PPO will be
denatured.
3.The pH of lime and lemon juice is in the range of 2.0
and 2.5, making them very effective against enzymatic
browning.
CONCLUSION
We conclude that the more acidic the solution
in which apples are soaked in, the slower the
rate of enzymatic browning of the apples.
From our results, lime juice is the most
effective in preserving the fresh-cut colour of
apples.