Why Do Apples Turn Brown?

Have you ever discovered that sliced apples turn brown after some time? Why do apples turn brown? It is because the apples get exposed to air which triggers an enzyme known as polyphenols oxidase. The biochemical reaction that creates the apple to turn brown is called enzymatic browning. This reaction enables the surface of a cut or injured apples to turn darker in color. To teach the concept of apples turning brown in an interesting way, you can conduct science experiments for kids

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Though children have seen the brown color on the surface of the sliced apples, they do not know the reason behind its change in color. Besides apples, there are also other fruits that turn brown in color when cut. Learning enzymatic browning can be one of the DIY science project ideas for kids. They can perform experiments at home and understand the biochemical reaction happening in the apples. 

What is an Enzymatic Browning?

Enzymatic browning is a biochemical reaction occurring in cut or sliced fruits exposed to oxygen that is triggered by an enzyme known as polyphenol oxidase. The oxygen and polyphenol oxidase (PPO) enzymes oxides to form o-quinones. The level of browning happens due to the level of PPO activity in the plant tissues. You can even avoid the enzymatic browning at home by following certain steps, such as dipping the fresh-cut apples in sugar syrup or lime juice. This reduces the oxidation process in the fruits by preventing them from turning brown in color. Besides this, fruits can be introduced into boiling water for some time in order to eliminate the PPO activity. 

Fun Facts about an Enzymatic Browning 

Some of the interesting facts about enzymatic browning are mentioned below:

  • There are three important factors responsible for enzymatic browning such as oxygen, polyphenol oxidase and phenolic compounds.
  • Cut or injured apples left open to oxygen turns brown in color. 
  • Polyphenol compounds are found inside the apple cells. 
  • The enzyme polyphenol oxidase is found in the chloroplasts of apples. 
  • When the apples are exposed to air, the cells are damaged, bringing together polyphenol oxidase and polyphenols. 
  • Exposure of apples to the air triggers the oxidation process leading to enzymatic browning. 
  • Polyphenols mixed with polyphenol oxidase and oxygen creates 1,2 Benzoquinone. 
  • The enzymatic browning process can be prevented by changing the temperature and PH levels of the apples. 

How Do You Prevent Apples from Turning Brown?

Simple ways to prevent apples from turning brown are mentioned below:

  • Prevent cut or injured apples from getting exposed to oxygen. 
  • Coat the sliced or cut apples with sugar syrup, lemon juice, vinegar or citrus juice in order to prevent oxidation of apples. 
  • Create a barrier between the surface of the cut apples and the oxygen by tossing it inside a bowl of water. 
  • Adding lemon juice to the cut apples reduces the level of PH and prevents it from turning brown. 
  • Avoid leaving cut apples in the air for a long period of time. 

Easy Science Project: Why Do Apples Turn Brown?

What do you observe in sliced apples after some time? Is it a brown color layer on the sliced portion of the apples? This is generally caused due to the enzyme that reacts with oxygen to form a brown color layer on the apples. The fruits get oxidized to turn brown in color. Why do apples turn brown? To know the concept behind its change in color, you can conduct an experiment for kids at home. 

Why Do Apples Turn Brown?

Aim of the Project

To experiment and observe the color turning brown in apples. 

Materials Required

  • Three apples 
  • A paper and a pen 
  • Labeling tape
  • Vinegar
  • Lemon juice
  • Bowls

Procedure

  • Keep a sliced apple in the bowl without covering the lid and label it as A. 
  • Keep a slice of apple filled with vinegar in the bowl labeling it as B.
  • Then, keep a slice of apple filled with lemon juice in the bowl labeling it as C. 
  • Keep all the three bowls of sliced apples at room temperature for 10 hours. 
  • After the given timeline, record the observations on a sheet of paper. 

Result 

It was observed that the sliced apple kept in a bowl without covering the lid turned brown in color compared to ones exposed to vinegar and lemon juice. The surface of the apple that was exposed to oxygen triggered an enzyme polyphenol oxidase to carry out an enzymatic browning reaction. On the other hand, the apples exposed to vinegar and lemon juice showed no change in color as the acids prevented enzymatic browning when it came in contact with air. 

Benefits of Learning about Why Apples Turn Brown?

Some of the benefits of learning about why apples turn brown are mentioned below:

  • Develops an understanding of the concept on why the apples turn brown.
  • Imparts knowledge on chemical reactions happening in the apples that enables them to turn brown in color when exposed to oxygen. 
  • Provides tips and tricks to prevent apples from turning brown using materials available at home. 
  • Enables children to understand about the different kinds of fruits and vegetables that can undergo enzymatic browning. 
  • Creates awareness about the quality of fruits among children by understanding the biochemical reactions. 
  • Enables children to understand about the enzymes involved in developing a brown color surface on the apples. 

To know more information, explore science games for kids, STEM activities for kids in the kids learning section at Osmo.

Frequently Asked Questions on Why Do Apples Turn Brown?

Why do apples turn brown?

The injured or cut apples are exposed to oxygen and polyphenol oxidase mixed with polyphenols to create a biochemical reaction known as enzymatic browning. This reaction enables apples to turn brown in color.

What are the benefits of learning about why apples turn brown?

The benefits of learning about why apples turn brown are that it helps children understand the concept with the help of science experiments effectively. Besides this, they will become familiar with the methods that can prevent apples from turning brown in color when exposed to air.