Why Apples Turn Brown in Packaging

Apples come in a wide variety of colors.

Polyphenol oxidase, also known as tyrosinase, is an enzyme contained in fruits and vegetables such as apples, pears, potatoes, and other starchy foods. When oxygen comes in to contact with the enzyme it causes the fruit to turn brown. Almost all plant matter contains polyphenol oxidase to some extent, but some fruits and vegetables are more susceptible to browning than others.

Packaging

Polyphenol oxidase is an enzyme found in apples.

The type of packaging used to store the fruit has a significant effect on how fast the fruit will turn brown. Storing fruit in plastic bags or containers retains oxygen, while paper bags help oxygen encircle the fruit. Allowing the fruit to "breathe" in this way helps prevent browning.

Function

Polyphenol oxidase plays a role in the defense mechanism of all plants.

Polyphenol oxidase enzymes are important in the defense mechanisms of plant species. The enzyme is thought to play a major role in fighting off disease, and healing wounded, growing plants. Cut an apple and you will notice that the exposed area quickly turns brown. This happens because the enzyme is collecting at the wound site, in an attempt to heal the cut. Once the enzyme is exposed to oxygen there is a chemical reaction which results in the brown color you see.

Types

Red, yellow, and green apples contain different levels of the enzyme.

Levels of polyphenol oxidase can vary according to the type of apple. The enzyme has a direct effect on the color of the fruit. Red, yellow, and green apples all contain different levels of polyphenol oxidase. This is why yellow and green apples tend to turn brown faster then red apples.

Considerations

Enzyme levels are effected by many variables.

Other variables in the level of this enzyme can include growing conditions, variety of fruit, and farming and harvesting practices. The level of polyphenol oxidase in a specific piece of fruit can change over time, as the fruit ages, as well.

Prevention/Solution

Keep your apples from turning brown by storing them in paper bags.

Keep apples from turning brown by storing them in paper, rather then plastic containers. Selecting fruits that have no visible scars or wounds is also a good way to prevent browning of the fruit. Choose fruit specimens based on overall freshness. Prevent polyphenol oxidase from collecting on the surface of the apple by treating with an acidic compound such as lemon juice.

References

• MD Idea
• Special Properties of Polyphenols