Objective
Apple slices turn brown very quickly when left in the air. This is caused by an oxidation reaction when the apple reacts with oxygen in the air. A particular enzyme in apples, called polyphenoloxidase, speeds up the oxidation of apples. In this activity, you will determine which preservatives are effective at preventing the oxidation (the browning) of apples.
Materials
30 mL (2 Tbsp) each of the following in labeled beakers or 3 ounce cups:
10% (w/w) ascorbic acid solution (vitamin C)
10 % (w/w) citric acid solution
Vegetable oil
10% (w/w) sodium chloride solution
10% (w/w) sugar solution
5 plastic cups per student
Marker
Knife
Round apple slices (7 slices per student)
Piece of plastic wrap (10 cm x 10 cm) per student
Forceps / tongs
Paper towels
10% (w/w) ascorbic acid solution (vitamin C)
10 % (w/w) citric acid solution
Vegetable oil
10% (w/w) sodium chloride solution
10% (w/w) sugar solution
5 plastic cups per student
Marker
Knife
Round apple slices (7 slices per student)
Piece of plastic wrap (10 cm x 10 cm) per student
Forceps / tongs
Paper towels
Procedure
1. Prepare solutions if not already made
2. Cut apple into 7 slices horizontally
3. Set one slice aside for control
4. Cover one with pastic wrap
5. Dip each of the slices into the solutions and label them
6. Take pictures and observe changes at 10min, 30min, 1 hour, and 1 day
2. Cut apple into 7 slices horizontally
3. Set one slice aside for control
4. Cover one with pastic wrap
5. Dip each of the slices into the solutions and label them
6. Take pictures and observe changes at 10min, 30min, 1 hour, and 1 day
Data
10 min 30 min 1 hr 1day
0 1 2 3 4 5
Not brown Very brown
Apple Slice 10 minutes 30 minutes 1 hour 1 day
In air (control) 3 4 4 5
Ascorbic acid 0 0 1 1
Citric acid 0 0 1 1
Vegetable oil 3 4 4 5
Sodium chloride 0 1 2 3
Sugar 1 1 2 4
Plastic wrap 1 2 3 4
Conclusions - Post Lab
1. Which substances were effective in preventing browning of apple slices?
There were two substances that were effective in preventing the browning of apple slices. Those were the ascorbic acid and the citric acid.
2. Did some of the treatments alter the smell, texture, or appearance of the slices? Which ones and how?
Yes, some of the treatments altered the smell, texture, and appearance of the slices. The smell was changed on the acids. the texture of the slice with oil was affected. The appearance of the apples were not greatly affected, only different stages of browning.
3. Is the treatment necessarily a good choice for a preservative just because it prevented browning? Why or why not?
No, It prevented the browning, but it involved covering the apple slice in a chemical. This changes the apple and its smell, texture, and appearance.
There were two substances that were effective in preventing the browning of apple slices. Those were the ascorbic acid and the citric acid.
2. Did some of the treatments alter the smell, texture, or appearance of the slices? Which ones and how?
Yes, some of the treatments altered the smell, texture, and appearance of the slices. The smell was changed on the acids. the texture of the slice with oil was affected. The appearance of the apples were not greatly affected, only different stages of browning.
3. Is the treatment necessarily a good choice for a preservative just because it prevented browning? Why or why not?
No, It prevented the browning, but it involved covering the apple slice in a chemical. This changes the apple and its smell, texture, and appearance.