Solidifying Science: Which Fruits Can Ruin Your Gelatin Dessert?
Have you ever noticed that if you’re making a gelatin dessert, like JELL-O, it’s not recommended to use certain fruits, like pineapple? Why is this? It’s because these fruits may prevent the gelatin from solidifying. In this activity you’ll get to determine if certain enzymes in some fruits are preventing the gelatin from solidifying, and whether there’s a way to still include these fruits without ruining your gelatin dessert!
This activity is not appropriate for use as a science fair project. Good science fair projects have a stronger focus on controlling variables, taking accurate measurements, and analyzing data. To find a science fair project that is just right for you, browse our library of over 1,200 Science Fair Project Ideas or use the Topic Selection Wizard to get a personalized project recommendation.
If you like making gelatin for dessert, you might have noticed that the box recommends against adding certain kinds of fruit, such as pineapple, kiwi, mango, ginger root, papaya, figs, or guava. People have a hard time getting the gelatin to solidify when they add these fruits. Gelatin is made from collagen, which is a structural protein found in all animals. Collagen is in many parts of the body and helps give animals their structure, or shape. Gelatin, which is a mixture of collagen proteins, solidifies when you cook it because its proteins form tangled mesh pockets that trap the water and other ingredients. When the gelatin cools, the proteins remained tangled. This results in your wiggly-jiggly gelatin dessert.
The fruits listed above contain proteases, which are enzymes. Enzymes help make certain chemical reactions happen. Proteases specifically act like a pair of scissors, helping reactions take place that cut other proteins up. In this activity you’ll explore whether these proteases are preventing the gelatin from solidifying (by cutting the gelatin into such small pieces that they are no longer able to tangle together and create a semi-solid structure). To do this you’ll inactivate these proteases by using heat.
Extra: In this activity you explored fruits that contain proteases, but many fruits do not contain proteases. You could repeat this activity using fruits that do not have proteases, such as apples, blueberries, oranges, raspberries, and strawberries. How well does the gelatin solidify when using fruits that do not contain proteases?
Extra: Meat tenderizer contains some of the same proteases that are found in the fruits explored in this activity. Try making a gelatin dessert with meat tenderizer (by dissolving 1 teaspoon [tsp.] of meat tenderizer in 1 tsp. of water and adding this to the 1 cup of gelatin liquid). Can gelatin solidify when it is made with meat tenderizer? If a solution of meat tenderizer is heated, is the enzyme deactivated?
Extra: You used heat in this activity to inactivate the proteases in fruit, but other temperatures and conditions may inactivate the proteases as well. Does freezing the fruit inactivate the proteases? Do other processes, such as drying or canning, inactivate the proteases? Does changing the pH of the gelatin and fruit mixture affect how well it solidifies?
Observations and Results
Did the cup with the raw fruit remain a liquid? Did the cups with the cooked fruit and no fruit added solidify like normal?
Normally the collagen proteins in gelatin form a tangled mesh that traps water and other ingredients in it, giving the gelatin its semi-solid form when it cools. However, proteases can cut up the proteins so that the gelatin cannot solidify. There are several different kinds of proteases in the fruits recommended for this activity, and using any of these fresh fruits should result in gelatin that does not solidify well, if at all. However, heating the fruit (through boiling or steaming) should inactivate the proteases, and the resultant gelatin mixture should solidify like normal (or nearly normal; because the fruit may have been hot when the gelatin was added, the gelatin may have been slightly less firm than in the cup without fruit). The proteases bromelian and papain (which come from pineapples and papaya, respectively) are often used in meat tenderizers. However, there are several other fruit proteases, such as actinidin (from kiwi fruit), ficin (from figs), and zingibain (from ginger).
More to Explore
Teisha Rowland, PhD, Science Buddies
Science Buddies |
Chemistry, gelatin, fruits, enzymes, heat
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