What's the Best Way to Stop Cut Fruits and Vegetables from Turning Brown?
Talk It Over
What happens to slices of potato, apple, or banana if you leave them in air too long? Is there any way to keep them looking fresh longer?
- Cookie sheet
- Masking tape
- 4 small bowls (or more)
- Water, lemon juice, vinegar, lemon-lime soda, or any other substance you would like to test
- Camera (digital or with film)
- Access to a computer or photocopier (to make black-and-white pictures)
- Your grayscale (See "How to Make a Grayscale" in Part III)
- Stick a piece of masking tape to the cookie sheet. On the tape, write your labels, equal distances apart: none, water, lemon juice, vinegar, lemon-lime soda, and any others you have decided to test. Use masking tape to label your bowls in the same way.
- Pour each of the liquids you will test into its labeled bowl. The liquid needs to be about 2 cm (1 inch) deep.
- Have an adult cut slices from the potato. Make the slices the same size, about 1 cm (less than ½ inch) thick.
- Put 1 slice in each bowl. Make sure the liquid completely covers the slices. Let the slices stay in the bowls for about 1 minute. Keep 1 slice out; don't put it in any bowl.
- Using the tweezers, lift the slices from their bowls 1 at a time. Let the excess liquid drip from the slice into the bowl. Then place the slice on the cookie sheet, next to its label. Put the slice you kept out next to the "none" label.
- Leave the slices for several hours. Check them often to see what changes you can observe.
- When you see obvious differences, take a picture of the slices. Use your computer to print a black-and-white picture, or make a black-and-white copy on a photocopier.
- Compare the colors of the slices to your grayscale. Assign each slice the number from the grayscale that best matches its color.
Careful slicing those potatoes! Kitchen knives are sharp and can cut your fingers.
Test water and lemon juice against nothing (the air). Tell which slice turns darkest and which stays lightest. Try to explain why.
Commercial products that protect the color and flavor of cut fruits and vegetables contain ascorbic acid (vitamin C). Purchase such a product (Fruit-Fresh is an example) to compare with fruit juices and your own preparation made from crushed vitamin C pills.
Or you might find out whether Fruit-Fresh, citrus juices, or other preparations give better results with some foods than others. Use the "Go" procedure to test and compare slices of apple, banana, peach, pear, apricot, or avocado. Another idea is to dry two batches of peaches, one with Fruit-Fresh and one without. Conduct a blindfold test of taste preferences, using your friends and family as test subjects.
Show Your Results
Make a table like this for "Go Easy":
|Liquid Tested||Circle the Result|
|None||Dark medium light|
|Water||Dark medium light|
|Lemon juice||Dark medium light|
For "Go," show your slices and your pictures. Make a table of your results and a bar graph that compares the grayscale values. Suggest reasons that might explain the differences you observe.
|Liquid Tested||Grayscale Value (1–10)|
|Lemon juice . . .and so on|
For "Go Far," makes tables and graphs to compare different test solutions and different fruits. If you conduct a taste test, make a table and a graph of people's preferences:
|Batch||Number of People Who Preferred|
|Dried (no treatment)|
|Dried with Fruit-Fresh|
Tips and Tricks
- Fruits and vegetables turn brown more quickly in a warm place. In a cool room,you may need to leave your experiment overnight. Your potato slices may turn darkest around the edges. You'll get better comparisons if you make your grayscale comparisons in the middle of the slice.
- To speed up the process,try whirling potato pieces in a food processor with a tablespoon of hydrogen peroxide. Can you explain why the potato browns so rapidly?
Warning is hereby given that not all Project Ideas are appropriate for all individuals or in all circumstances. Implementation of any Science Project Idea should be undertaken only in appropriate settings and with appropriate parental or other supervision. Reading and following the safety precautions of all materials used in a project is the sole responsibility of each individual. For further information, consult your state’s handbook of Science Safety.