Why Do Apples Turn Brown?

Summary

In this educational video, EJ explains the science behind why fruits like apples and bananas turn brown. This process, known as enzymatic browning, occurs due to chemical reactions involving enzymes and phenols in fruit cells. EJ dives into how oxidation and melanin production are key factors in this natural phenomenon, which also serves to protect the fruit from damage. The video explores practical tips to slow down browning, such as using acidic liquids like lemon juice, and the role of ethylene gas in fruit ripening. Viewers are encouraged to experiment with fruit storage and learn about the fascinating science behind these changes.

Takeaways

• 😀 Enzymatic browning occurs when fruits like apples and bananas turn brown after being exposed to oxygen or damage.
• 😀 This process is driven by an enzyme called polyphenol oxidase (PPO) that interacts with phenols in the fruit.
• 😀 The chemical reaction of PPO with phenols produces melanin, the same pigment responsible for skin color in humans.
• 😀 Melanin production in fruit is a natural protective mechanism that helps prevent further damage and discourages insects and animals from eating the fruit.
• 😀 Enzymatic browning is a form of oxidation, which is also responsible for changes in other plants and foods, like chocolate.
• 😀 While browning fruits might not look appealing, it’s not harmful to eat them—it’s simply a cosmetic change.
• 😀 Cutting or bruising fruit exposes the flesh to oxygen, triggering enzymatic browning as a protective response.
• 😀 Certain acids, like those found in lemon juice, can slow down the browning process by inhibiting the PPO enzyme.
• 😀 Storing fruit in water or highly acidic solutions can help preserve its appearance and reduce oxidation.
• 😀 Ethylene gas, a naturally occurring plant hormone, accelerates the ripening process and browning in fruits like bananas.
• 😀 Fruits with high ethylene production, like bananas, ripen faster and may cause nearby fruits to ripen more quickly when stored together.
• 😀 Freezing ripe fruit is an effective way to preserve it for later use, such as in smoothies or homemade ice cream.

Q & A

What causes fruits like apples and bananas to turn brown?

The browning of fruits like apples and bananas is caused by a chemical reaction called enzymatic browning. This process occurs when an enzyme called polyphenol oxidase (PPO) interacts with phenols in the fruit, leading to the production of melanin, which gives the fruit its brown color.

What is the role of polyphenol oxidase (PPO) in the browning of fruit?

Polyphenol oxidase (PPO) is an enzyme found in fruit that reacts with phenols. When the fruit is exposed to oxygen (e.g., when it is cut or bruised), PPO accelerates the oxidation process, leading to the formation of melanin, the brown pigment.

How does enzymatic browning protect the fruit?

Enzymatic browning helps protect the fruit by discouraging insects and animals from eating it. The brown, mushy appearance is unappealing, which may prevent further consumption. Additionally, the process of producing melanin slows down the rotting process within the fruit.

Is the brown color on fruits like apples and bananas harmful?

No, the brown color on fruits like apples and bananas is not harmful. It’s a natural process due to oxidation and enzymatic reactions. While the texture and taste might change slightly, the fruit is still safe to eat unless it has fully rotted.

Why do some fruits, like bananas, ripen and turn brown faster than others?

Fruits like bananas produce higher levels of ethylene, a gas that acts as a hormone for ripening. This high ethylene production leads to faster ripening, which in turn accelerates the browning process.

How can you slow down the browning of fruit?

To slow down the browning of fruit, you can limit its exposure to oxygen, such as by placing fruit slices in water. You can also use acidic liquids like lemon juice, which interfere with the PPO enzyme and prevent the oxidation process from completing.

What are some other liquids that can help slow down enzymatic browning?

Other liquids that can slow down enzymatic browning include clear soda, carbonated water, salt water, and vinegar. These liquids can alter the environment around the fruit, preventing the PPO enzyme from functioning efficiently.

How does ethylene gas affect fruit ripening?

Ethylene gas is a natural hormone in fruit that triggers ripening. The more ethylene a fruit produces, the faster it ripens. Fruits like bananas produce large amounts of ethylene, which is why they ripen and turn brown faster than other fruits.

Can placing unripe fruit in a paper bag with a banana help it ripen faster?

Yes, placing unripe fruit, like a green banana or avocado, in a paper bag with a ripened banana will cause the unripe fruit to ripen faster. The ripened banana produces ethylene, which accelerates the ripening process of nearby fruit.

What should you do with ripe fruit if you want it to last longer?

To make ripe fruit last longer, you can store it in a cool place to slow down the production of ethylene and the ripening process. Alternatively, you can freeze ripe fruit to preserve it for later use, such as in smoothies or homemade ice cream.