![]() Plastic wrap is often used in food preparation and storage to prevent oxygen exposure thereby preventing oxidation. Coating freshly cut apples with sugar, syrup or oil can reduce the amount of available oxygen and thereby slow the browning reaction. Another method involves inactivation or lowering the activity of the enzyme catalyzing the reaction. Since oxygen plays a crucial part in the reaction, preventing it from entering the cells is one way of preventing the enzymatic browning of your apple. How to Keep Your Apple from Turning Brown It is the formation of these pigments that is responsible for the harmless but unappetizing discoloration of your apple. In the presence of oxygen, the enzyme oxidizes the colorless phenolic compounds into dark colored melanin pigments. Under normal circumstances, the cell membrane acts as a barrier between the enzyme and the air’s oxygen, but when the cell is damaged (bruised of cut) the barrier is broken. An apple contains lots of little cells, each protected by a cell membrane. When exposed to oxygen, the PPO enzyme will turn some colorless pheonolic compounds, that are also present in the apple, into brownish pigments known as melanins. ![]() Apples contain an enzyme called polyphenol oxidase (PPO). So, what has really happened? An oxidation has occurred but a pigment rather than rust has been formed. cellular respiration where oxidation of glucose to carbon dioxide yields energy. Oxidation is responsible for bronze roofs and statues developing a greenish patina and the reaction also plays a crucial role in many biological processes e.g. In chemical terms, an oxidation is a reaction where a substance looses an electron when interacting with another substance. The words oxidation and rust are often used interchangeably, however, not all oxidations form rust. An apple without skin only contains 0.0007% iron, so the amount of rust formed would be negligible and probably not even visible. To produce rust, also known as iron oxide (Fe 2O 3), iron has to be present. But just because it looks like rust, does not necessarily mean that it is. If you do a quick google search, several so-called science websites will tell you that your apple has rusted due to oxidation. Rust is formed when iron is exposed to oxygen and moisture.
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