Labs & Activities › Pineapple and gelatin lab
Enzyme Lab: Why Fresh Pineapple Ruins Gelatin
Gelatin sets into a gel, but fresh pineapple can keep it liquid. The reason is an enzyme, and heat can stop it.
- 20 minutes to set up, 1 or more hours to set
- Groups of 3–4
- No smell
- Biology BIO.1B.2
- Foundations FB.2.6
Question
Why does fresh pineapple stop gelatin from setting, and what happens when the pineapple is heated?
Background
Gelatin is made of protein chains that tangle together to form a gel. Fresh pineapple contains bromelain, an enzyme that breaks down protein. If bromelain is active, it cuts the gelatin chains and the gelatin stays liquid. Canned pineapple is heated during canning, which can denature the enzyme.
- enzyme
- protein
- substrate
- denature
- independent variable
- dependent variable
- control
Plan your investigation
Write a hypothesis in the form If …, then …, because …. Each group tests these four treatments, with three cups of each:
- Water (control)
- Fresh pineapple juice
- Canned pineapple juice
- Fresh pineapple juice that was boiled for 3 minutes and then cooled
Independent variable: the liquid added. Dependent variable: firmness score. Keep constant: amount of gelatin, amount of liquid added, temperature, and setting time.
| Score | What you see |
|---|---|
| 0 | Completely liquid; pours like water |
| 1 | Thick liquid; barely coats the spoon |
| 2 | Soft; slumps when the cup is tilted |
| 3 | Mostly firm; moves slightly when tilted |
| 4 | Firm; holds its shape when the cup is tilted |
Safety
- Do not eat or drink anything made in the lab. Check for pineapple, kiwi, and gelatin allergies before the lab.
- Use hot water only under teacher supervision, and keep it away from the edge of the table.
Materials
- Gelatin (plain or fruit-flavored, not sugar-free if your brand does not set well), prepared by your teacher
- 12 small clear cups, labels, and a marker
- Fresh pineapple juice, canned pineapple juice, water
- Pot or kettle and hot plate for boiling juice (teacher)
- Spoons, tape, refrigerator
Procedure
- Your teacher prepares the gelatin using the package directions and lets it cool until it is warm, not hot.
- Label 12 cups: four treatments, three cups each. Pour the same amount of warm gelatin into each cup (for example 50 mL).
- Add the same amount (for example 10 mL) of each treatment liquid to its cups and stir gently with a clean spoon.
- Place all cups in the refrigerator on a tray. Leave them for at least 2 hours, or overnight.
- Tilt each cup gently and score the firmness from 0 to 4. Record the scores.
Data
Analysis
- Which treatments kept the gelatin liquid? Use your firmness scores as evidence.
- What was the purpose of the water control?
- Gelatin is a protein. Explain how bromelain keeps it from setting.
- Canned and boiled pineapple let the gelatin set. Explain why, using the word denature.
- Kiwi and papaya also contain protein-digesting enzymes. Predict what would happen if you used fresh versus canned kiwi, and explain your prediction.
- Write a claim-evidence-reasoning answer that explains your results.
Teacher notes
Preparation and tips
- Make the gelatin ahead of time and keep it warm. Hot gelatin can denature the enzyme, so let it cool until it is just warm.
- Test the fresh pineapple juice before class. Very ripe pineapple has more active enzyme, and old juice loses activity.
- Use the same brand of canned pineapple each year so results are consistent.
What to expect
- The water control sets firmly. Fresh pineapple juice usually stays liquid or very soft. Canned and boiled fresh juice usually set.
- If every cup sets, the juice may be too old or the gelatin too hot when mixed. If every cup stays liquid, the gelatin may not have been strong enough.
Alignment
- Biology BIO.1B.2 and BIO.1B.1 (proteins); Foundations FB.2.6. Science and engineering practices: plan and conduct investigations; analyze and interpret data.