Home experiment to understand how natural preservatives work
We have been talking a lot about natural food preservatives in the background of the pandemic. Indians have used spices, lemon, curd and other natural preservatives successfully for centuries. Demonstrate how it works through this simple home experiment for kids.
What will you need for the experiment?
You will need some easily available items:
- An apple
- Knife
- 2 lemons
- Small bowl
- Clock/timer
- Paper plates
- Pen and paper
Assemble these on a table, call the kids, and start the experiment.
How to do the experiment?
Here is a step-wise guide for your school student to follow.
1. Make to labels with the pen and paper, one reading ‘control’ and the another ‘lemon’
2. Squeeze the lemons completely into the bowl
3. Slice the apple in half
4. Place half an apple with the cut end below in the bowl of lemon juice, and leave it for two minutes. Place the ‘lemon’ tag next to it. Place the ‘control’ tag next to the other half apple
5. Ask your kids to observe the colour of the whites of both apple halves
6. They are to observe the apples again after 10-minutes, 20 minutes, and 30 minutes and an hour, and note the difference in colour. They can even continue to look at the apples every hour for the whole day.
What is the result of the experiment?
As the kids observe, the apple without the juice becomes brown, while the one dipped in lemon juice remains white.
How do you explain the experiment?
When an apple is cut open, an enzyme (protein causing chemical reactions) called polyphenol oxidase is released by the apple, and it reacts with the oxygen in air. This causes the fruit to turn brown, like rust forming on iron. This chemical is a defence mechanism of plants. The brown area discourages animals and insects from eating the rest of the plant. The browning also has antibacterial effect, limiting the spread of germs.
Lemon juice acts as a preservative. It contains ascorbic acid (an isolate of Vitamin C) and has a low acidic level. Ascorbic acid reacts with oxygen before polyphenol oxidase. The low acidic level of lemon juice helps in keeping the polyphenol oxidase inactive, preserving the fruit.