Determine what causes a banana to turn brown after it is peeled with a simple science experiment.
Once cut, bananas, like apples, pears and other fruits that produce polyphenol oxidase, quickly begin to turn brown. Though it's not harmful to eat fruit that has begun to turn brown, it makes the fruit look less appetizing. By conducting a simple science experiment, perfect for a science fair, you can determine not only what causes a fruit to brown but also slow the process -- a valuable lesson for those interested in agricultural or food industry careers.
Preparation
Fill six bowls with different liquids, such as lime juice, orange juice, water, salt water, vinegar and oil. Label the bowls using sticky notes or masking tape. Use pH strips to test the pH level of each liquid and take note of the ingredients (including vitamin content) listed on each liquid's container. Peel and cut one or two bananas into 1-inch-thick slices. Place two slices of banana in each bowl. Set two slices of banana aside on a paper plate as a control sample; these slices of bananas will allow you to compare the results of the treated banana to an untreated sample.
Observation
Draw an observation chart that includes a column for each type of liquid, as well as a column for the control sample. Next to each column, write down different amounts of time, such as 15 minutes, 30 minutes, 1 hour, 2 hours, 4 hours and 8 hours. Observe your banana samples at the set time segments and record your observations on the chart. Take photographs of the samples for further documentation.
Conclusion
Review your observation data to determine which liquids worked best to prevent browning in your . Compare the pH levels of the liquids, as well as the ingredients (including vitamin content), and determine which pH levels and which ingredients work best for delaying or preventing browning. You will find that liquids with lower pH and more vitamin C perform best.
Explanation
Bananas and other fruits produce polyphenol oxidase when cut. Polyphenol oxidase reacts with oxygen, causing browning. High levels of absorbic acid (vitamin C) deter browning because polyphenol oxidase reacts to absorbic acid more quickly than it reacts to oxygen. Low pH levels deter browning because polyphenol oxidase functions most efficiently at higher pH levels (between 5 and 7).
Further Experimentation
Now that you have determined the effectiveness of vitamin C and low pH levels in delaying or preventing bananas from browning, experiment using alternative compositions. Crush vitamin C tablets or multivitamins and sprinkle them on banana slices. Soak banana slices in different types of juices, such as cranberry, apple, grape and grapefruit. Try soaking the banana slices in other liquids, such as Kool-Aid, sugared lemonade, soft drinks or carbonated water. Compare the results of your alternative experiments to the results from your original experiment.
Tags: , polyphenol oxidase, absorbic acid, banana samples, because polyphenol, because polyphenol oxidase