Agriculture and Food 7–12 · Years 11–12
Gelation and protease enzymes: fresh and canned pineapple in jelly
Food Quality: functional properties of food
The idea
Gelatine sets because its protein chains form a network that traps water, and protein-digesting enzymes in fresh pineapple and kiwi fruit cut those chains so the jelly stays liquid unless heat has denatured the enzymes.
Safety card
Hazards
- scalds from kettle water
- kiwi fruit and pineapple allergies
- knife cuts
Controls
- teacher pours boiling water
- check allergy records
- cut on a board
Note
Food handling follows the FSANZ food safety standards (Standard 3.2.2) as explained on the FSANZ food temperature and thermometers page; check class allergy and anaphylaxis records before any food is prepared; the Food Technology Years 7–10 Syllabus reminds teachers that food allergies can cause anaphylaxis. Heat: complete a RiskAssess or school risk assessment for boiling water.
What you need
- gelatine powder or leaves, enough for 600 mL of jelly made to the packet directions
- fresh pineapple, crushed and strained to juice; canned pineapple juice; fresh kiwi fruit puree
- fresh pineapple juice boiled for 5 minutes and cooled
- agar powder for the extension
- 6 cups or moulds, measuring cylinders, kettle, refrigerator, labels
How to do it
- Make the gelatine solution to the packet directions and let it cool, stirring now and then, until it is lukewarm but still pourable, so its heat does not denature the fruit enzymes; then pour 80 mL into each of five cups.
- Stir 20 mL of one of the following into each cup: water (control), fresh pineapple juice, canned pineapple juice, boiled fresh pineapple juice, kiwi puree.
- Refrigerate all cups together and check each by tilting after 2 hours and the next day.
- Extension: set agar with fresh pineapple juice in the same way and compare.
- Explain each result by what the enzyme does to the gelatine and what heat does to the enzyme.
What you should see
The control, canned-juice and boiled-juice jellies set; the fresh pineapple and kiwi jellies stay liquid. The RSC article explains that bromelain (pineapple) and actinidain (kiwi fruit) break gelatine's chains and that heating before canning denatures bromelain. The agar jelly sets even with fresh pineapple, because agar is a seaweed gelling agent, not a protein. The learner knows it worked when the water control sets firmly.
What changes
- What you change
- fruit addition (none, fresh, canned, boiled, kiwi)
- What you measure
- set or not set by the tilt test at 2 hours and next day
- What you keep the same
- gelatine concentration
- volume added
- refrigerator temperature
- setting time
Common misconceptions
Each of these ideas is wrong, and the activity is a chance to test it.
- Fresh fruit stops jelly setting only because it is too watery.
- Gelatine comes from plants.
- Canned fruit contains the same active enzymes as fresh fruit.
Curriculum references
The NSW syllabus outcomes and Australian Curriculum v9 codes this activity supports. They are references, not a verified or complete curriculum alignment.
Sources
The pages the author read to write this activity.