Why do mashed potatoes stay white?

Question:

Why does a freshly cut potato turn brown when left standing, but why do mashed potatoes stay white?

Answer:

The enzyme denatures during cooking thereby mashed potatoes remain white.

Explanation:

Mashed potatoes are cooked. The heat from cooking them denatures the enzyme Catecholase which causes raw potatoes to turn brown through oxidation when they are exposed to air. When potatoes are freshly cut, the enzyme Catecholase in the cells is exposed to air, causing a chemical reaction that turns the potato brown. However, when potatoes are mashed and then cooked, the heat from cooking denatures the enzyme Catecholase, preventing it from causing the browning reaction. As a result, mashed potatoes remain white even after being exposed to air.