What it shows
Jelly sets because gelatin proteins link into a net, but fresh pineapple contains an enzyme, bromelain, that cuts proteins and stops the net forming. Heated or tinned pineapple has lost the enzyme, so the jelly sets normally.
The science
Gelatin is a protein whose long molecules tangle into a gel as they cool. Bromelain in fresh pineapple is a protease enzyme that breaks the protein chains into small pieces, so they cannot hold water in a net. Heat above about 70 C changes the shape of the enzyme and destroys its action.
Materials
Cost: under Rs 200. Many items come from home or from waste; spare parts such as LEDs, motors and wire are in the store.
- 1 packet of gelatin jelly crystals
- Fresh pineapple pieces
- Boiled or tinned pineapple pieces
- Hot water and cold water
- Six small identical cups
- A fridge
- A spoon and sticky labels
Safety
For this project: An adult must pour the hot water and cut the pineapple. Fresh pineapple can irritate the mouth, so do not eat the test cups, and check for allergy.
Never use mains electricity: power models with cells, batteries or a low-voltage adapter. Sharp and hot tools, flames and lab chemicals need an adult or your teacher beside you. Keep magnets, button cells and small parts away from young children, and wash your hands after making.
All the safety rulesStep by step
7 steps. Do them in order, and test each part before you go on to the next. Write what you notice in a notebook as you go.
Ask an adult to make up the jelly with hot water as the packet says, and let it cool a little.
Pour equal amounts into six cups and label them.
Add fresh pineapple pieces to two cups, boiled pineapple to two cups and nothing to two cups.
Stir gently and place the cups in the fridge.
Check every hour by tilting a cup to see whether the jelly holds its shape.
Look again after 8 hours and also the next morning.
Record which cups set, which stayed liquid, and compare the texture of the set ones.
What you should see
The cups with fresh pineapple stay runny or set only weakly, while those with boiled pineapple and the plain jelly set firmly. This shows enzyme action.
Viva questions
A teacher or a judge will ask how it works. Try to answer each question before you open it, then compare.
1What type of substance is gelatin?
A protein.
2What does bromelain do?
It breaks proteins into smaller pieces.
3Why does boiling fix the problem?
Heat destroys the enzyme.
4Name another fruit with a similar enzyme.
Papaya, with papain, or kiwi.
Take it further
Use papaya in a jelly cup and compare its power with pineapple.
Change one thing, measure what happens, and add a table or chart of your readings: that is what turns a model into your own investigation.
Free ebooks for this project
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