The science behind our food
Have you ever bit into an apple and after a while of forgetting it, you have found it to be brown? I think it’s happened to all of us!
To learn the reasons why some fruits and vegetables turn brown, we recommend doing the following experiment.
You will need the following materials:
✔ 1 apple cut into 6 slices
✔ 6 plastic cups or containers to accommodate the apple pieces
✔ Paper to mark each glass or container
✔ Juice of one lemon dissolved in half a cup of water
✔ 1 cup clear soda like 7-Up or Sprite
✔ Baking soda (1 tablespoon dissolved in 1 cup of water)
✔ Sugar (1 tablespoon dissolved in 1 cup of water)
✔ 1 cup of water
⛔ With the help of an adult, cut an apple into 6 equal-sized slices. Try to only use one apple since, if you include others, you are adding variables to the experiment. Then place each piece of apple in a glass or container large enough to completely cover it with each liquid. As a control, one of the slices will remain without any liquid and another will just be covered with water. Write the names of the liquids and stick them in the corresponding container so you don’t confuse them. Top each apple slice with one of the liquids. Now, make your predictions! What do you think will happen to the apple pieces? Some of these solutions will prevent apples from turning brown (rusting). What solution do you think it is and why?
Comparing the apple slice with no liquid in it to the others, it is clear that the lemon juice and clear soda keep the apple from turning brown. Both of these liquids contain ascorbic acid (vitamin C) and have a low pH level. Ascorbic acid works because the oxygen in the air reacts with it before it reacts with the enzymes in the apple. Once the ascorbic acid is depleted, the oxygen in the air will begin to react with the enzymes in the apple and browning will occur. Of these two solutions, the one that contains the greatest amount of ascorbic acid is lemon, which is why it was the most effective. However, both the lemon and the clear soda changed the flavor of the apple.
The sugar also decreased the time the apple turned brown, but changed its distinctive flavor making it much sweeter. The water prevented the piece of apple from oxidizing for a short time, this is because it protected it from the oxygen present in the air.
For its part, baking soda, unlike acids, has a high pH, which means it is more alkaline. Substances with a high pH contain higher amounts of oxygen. Therefore, exposing a slice of apple to baking soda can cause it to turn brown even faster.
Oxidation is not unique to apples. Pears, potatoes, plantains, bananas and aubergines among others, are also browned.