Not just Apple but also Potato or even Banana turns brown after some time of cutting them into slices. Let us find out why.
All cells contain thousands of enzymes. These enzymes do all of the work necessary for the cell to live its life.
The actual mechanics that causes browning in apples and potatoes involves an enzyme called 'Polyphenol oxidase', also known as 'tyrosinase, and an amino acid called 'Tyrosine'.
Amino acids are used to build proteins. Once you cut the fruit, you open up some of the cells and expose them to the oxygen in the air.
Oxygen combines with tyrosine to make dark stuff called 'Melanin' and tyrosinase speeds up the process. That's why a cut apple darkens. And the same thing happens to a cut banana or potato.
The easiest way to prevent browning is to put the sliced apples, bananas, or potatoes in water so that the enzyme does not have access to Oxygen or just seal them into the vacuum packet.