Apple Browning Project

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					     Gan Eng Seng School Presents

                Apple Browning
The effect of different PH levels on apple browning.
      To determine the pH range that is
      most effective in slowing down the
      enzymatic browning of apples

•   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.
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


 •   Red apples               •Stirring Rod

 •   Lime (pH 2.38)           •Tea spoon

 •   Lemon (pH 2.49)          •Electronic balance

 •   Distilled water (pH 7)   •Knife

 •   Common salt (sodium      •Chopping Board
     chloride) (pH 7)
                              •white paper

•   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
                                                          showing a 5
    of white paper
                                                          cm x 5 cm
•   The apple slices were labeled with the name of
    the solution it was dipped in accordingly.
                                                          apple slice
•   Photographs of the apples were taken at 1 hour
    intervals for a total of 5 hours to show the colour
    changes in the apples
  Lime          Lime


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.
• 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.
• 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

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.
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.