Real Life Science Project

Keeping Apples Fresh

Questions to think about: Why does lemon juice keep apples from turning brown? Would a different type of juice work better?

Topic- Fresh Apples

Purposes of the study- What is the best way to keep apples from turning brown?

Research questions/ hypotheses- My hypotheses is that I think lemon juice is the best way to keep apples from turning brown.

Materials: apple, lemon juice, lime juice, cranberry juice, sharp knife, and clock

Process:

1. Cut the apple in half from top to bottom.
2. On one apple half, lightly coat the white part of the apple with lemon juice. Leave the other half uncoated. (The uncoated half is your "control" sample and let's you see what normally happens to a cut open apple.)

3. Observe the color of both apple halves, then place them white-part-up on a counter or tabletop.
4. Observe the apples again after 30 minutes. Notice any color changes and/or differences in appearance.
5. Look at the apples again periodically throughout the day. What do you find?

Results and Findings

After doing this experiment, I discovered that the lime and lemon juice both produced the same results. Also, the cranberry juice produced the same results as the control apple with no juice applied.
Things to consider during the experiment:

1. Amount of juice applied to each apple
2. Whether the fruit is fresh or not
3. Cutting the apple into halves takes longer to see results than cutting the apple into fourths

Discussion and Conclusions

When an apple is cut open, an enzyme called polyphenol oxidase is released from the cells of the apple and reacts with the oxygen in the air. This reaction causes the fruit to turn brown, similar to rust forming on metal. Almost all plants contain polyphenol oxidase, and it is believed plants use this enzyme as part of a defense mechanism. When a plant is damaged, the browning of the affected area is thought to discourage animals and insects from eating the plant any further. It also might help the plant heal because the browning creates an antibacterial effect, preventing germs from destroying the plant even more.

Lemon juice helps keep the apple from browning, because it is full of ascorbic acid (Vitamin C) and it has a low (acidic) pH level. Ascorbic acid works because oxygen will react with it before it will react with the polyphenol oxidase. However, once the ascorbic acid gets used up, the oxygen will start reacting with the enzyme and browning will occur. Lemon juice's low pH level also helps prevent browning. Polyphenol oxidase works best when the pH level is between 5.0 and 7.0. However, below a pH level of 3.0, the enzyme becomes inactivated. The pH of lemon juice is in the 2.0 range, making it very effective against browning. Lime juice and cranberry juice also have a pH below 3.0.

Click below for references and extended resources or acknowledgment:

http://www.hometrainingtools.com/article.asp?ai=1461&bhcd2=1270475863
http://www.indiacurry.com/chutney/foodphlevel.htm