Reducing the Browning of Apples

Introduction:

When many types of fruits and vegetables are bruised or injured, surface browning occurs rapidly. Enzymatic browning requires four different components: oxygen, an enzyme, copper, and a substrate. To prevent browning at least one of these components must be removed. One way to reduce browning is to lower the pH by 2 or more units below the optimum pH, in order to inactivate the enzyme. Ascorbic acid is used commercially to prevent enzymatic browning. It acts as both an acidulant and antioxidant.

Preparation:

In this lab you can use materials that are commonly found in kitchens. Use items that are familiar to students. This lab takes about 5 minutes to set up.

Materials:

8 small plastic plates or petree dishes
8 small cups
Salt
Sugar
Sprite
Lime juice
Lemon juice
Pineapple juice
Fresh fruit preservative
pH paper
Golden Delicious Apples (for best results)

Procedures:

  1. Set up all the solutions out and let the students pick at least four or you may want to let them try all the solutions.
  2. Pour a small amount (about 1 inch in depth) of solutions in each cup. Make sure to label the cups.
  3. Label plates and set next to cups
  4. Label one of the plates as the control so you will have a reference point.
  5. Take the pH of each solution and record.
  6. Cut the apple into pieces.
  7. Place the pieces of apples into the solution for 30-60 seconds and then place the apple piece on the plate.
  8. Determine the degree of browning over time and record your observations. Some samples may have to set out over night to see notable differences. (This is optional)

Results:

Solution pH Browning (yes or no)
     
     
     
     
     
     
     
     

Prelab Questions:

  1. Which apple piece will brown first?



  2. Which solution do you think will work best for preventing browning?



  3. Why do you think this solution (answer to #2) will work the best?



Post Lab Questions:

  1. Which apple browned the fastest?



  2. Which apple(s) did not brown?



  3. Why do you think the apples did not browned?



  4. Did any of the results surprise you from your predictions? Which ones?



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