Last week in the Lab Report, we saw enzymes in action. Today, I want to show you an apple experiment that will allow you to see enzymes in action and show you how to prevent the same enzyme activity.
Apples contain an enzyme called polyphenol oxidase (phenolase). When an apple is cut, the enzymes inside are released. Oxygen from the air causes phenolase to catalyse (speed up the process) the formation of brown pigments called melanins. This is called oxidation or enzymatic browning. It’s kind of like rust forming on metal – another form of oxidation.
I’m sure you have seen this process occur. Just think what happens to cut apples and bananas when left out on a counter for a while. They turn brown and unappealing. Certain substances can stop or slow down this process. Today, we are going to test one such substance.
For today’s experiment, you will need one apple cut in half and a couple vitamin C tablets.
First, crush a couple of vitamin C tablets.
Sprinkle one half of a cut apple with the crushed vitamin C tablets.
Set the two apples halves – one with the vitamin C and one without- side by side. Observe them over time. What do you see? Keep track of each apple every 15 minutes for the next hour or two. What is happening to the apples? Are they different or the same?
What you should observe is browning occuring in the apple without the vitamin C within the first 30 minutes, while the apple with the vitamin C should remain unchanged at first. You may see overtime the vitamin C apple will start to brown a bit. The ascorbic acid in the vitamin C tablet doesn’t stop the enzymes from reacting. Instead, the oxygen reacts with the ascorbic acid before the enzymes, therefore stalling the enzymatic browning. However, once all the ascorbic acid reacts with the oxygen, the oxygen will then react with the enzymes and cause the browning of the apple.
Try this for yourself and let me know your results!