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Science Demonstration of the Enzyme Bromelain
Why Fresh Pineapple Cannot Be Used in Jell-O
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Enzymes are molecules that speed up chemical reactions in living things. These organic molecules are like little machines that make specific chemical reactions run faster, but are not used up in the reactions that they facilitate.
Denaturing an Enzyme
Enzymes are primarily made of proteins, large organic molecules with distinct three-dimensional shapes. The shape of enzymatic proteins is important in allowing the enzyme to work properly. Shape is crucial because the area of the enzyme where the substrate reactant binds to the enzyme (the active site) fits like a lock and a key. If the shape of the active site (the lock) changes, the substrate that the enzyme alters (the key) won’t fit.
Deactivating an enzyme by changing its shape is called denaturation. The effect can be achieved several ways, including:
- exposing the enzyme to high temperatures
- changing the pH
- non-competitive inhibition, where another chemical binds to the enzyme, changing the shape of the active site
Fresh Pineapple and Jell-O™
Jell-O™ is made of gelatin, a processed version of a structural protein called collagen that is found in the skin and bones of animals. Although Jell-O™ is often eaten plain, fruit is also sometimes added. When that fruit is pineapple, it can interfere with Jell-O™ solidifying.
Pineapple contains the enzyme bromelain, which can digest collagen protein. Adding fresh pineapple to Jell-O™ allows the bromelain to break down the gelatin’s collagen, and the Jell-O™ will not set upon cooling.
If instead of fresh pineapple, canned is used (cooked as part of the canning process), the bromelain is denatured and cannot facilitate the breakdown of gelatin. Using canned pineapple allows the gelatin to firm and set.
Classroom Demonstration of Heat Denaturing Enzymes
This lesson works best as a demonstration prepared ahead of time by the instructor, rather than as an in-class experiment. The instructor should prepare a batch of Jell-O™, and divide it into two plastic containers that can be sealed. To one batch, add fresh pineapple, to the other batch add canned. After teaching the class about enzymes, denaturation, the composition of Jell-O™, and the specific enzyme bromelain, show the students the two batches of prepared Jell-O™. Pass these samples around the room so that the students can get a close up look. Then ask why one batch would set and the other would not. Students may need to be prompted about what the canning process entails (the application of high heat) in order to solve the riddle.
Sources
- Campbell, NA and Reece JB (2005) Biology. Seventh Edition. Pearson Education, Inc.
- Thorpe, P. ed. (2007) Biology 120 General Biology I: Laboratory Experiments & Exercises. Grand Valley State University.
This article originally appeared on Suite101 online magazine.
Page last updated 2/4/2012
Article Summary: Have you even tried to make Jell-O with fresh pineapple in it? If so, you've been disappointed. Here's why, with a classroom demonstration for teaching about enzymes.
Science Demonstration of the Enzyme Bromelain
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Bromelain Experiment: Container on light is Jell-O made with canned pineapple (gelatin is set). Container on right is Jell-O made with fresh pineapple (gelatin is liquid).
