Why do apples and potatoes turn brown when sliced; apples and other produce e.g., pears, bananas, peaches, potatoes contain an enzyme called polyphenol oxidase or tyrosinase .
Which reacts with oxygen and iron-containing phenols present in the apple, pears, bananas, potatoes etc. This enzymes do all of the work necessary for the cell to live its life.
#Fact 1: The browning reaction results from the oxidation of phenolic compounds in the fruit under the action of an enzyme called polyphenol oxidase (PPO), which is common in plant tissues.
Once you cut the fruit, you open up some of the cells. The enzyme then has access to oxygen in the air and it does its thing, turning the fruit brown.
This is the same thing that causes brown spots in apples when you drop them.
Technically, an enzyme called polyphenol oxidase (also known as tyrosinase), which is comprised of monophenol oxidase and catechol oxidase enzymes, when exposed to oxygen will result in phenolic compounds in the apple tissue turning into ortho-quinones or “o-quinones.”
O-quinones are what is providing the protection from bacteria and fungi as they form a natural antiseptic.
O-quinones themselves have no color, but they further react with amino acids and oxygen to produce melanin, which is how we get the brown color on the cut cells of the apple.
How to Prevent Apple from Browning
- Prevent browning by putting the sliced apples in water so that the enzyme does not have access to oxygen.
- You can also heat the apples to denature the enzyme.
- Slowed or prevented the reaction by inactivating the enzyme with heat (cooking).
- Reducing the pH on the surface of the fruit (by adding lemon juice or another acid).
- Adding certain preservative chemicals (like sulfur dioxide).
In humans, tyrosinase is also important because it helps create melanin, which causes tanning.
The lack of tyrosinase in humans leads to albinism. So in humans, the browning that tyrosinase helps cause is actually a good thing!
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