Question: Why Do Cut Apples Pears Bananas and Potatoes Turn Brown?

1. Does lemon juice (or orange juice) prevent fruit like apples and bananas from turning brown when exposed to air?

2. Question: Why Do Cut Apples Pears Bananas and Potatoes Turn Brown? Answer: Apples and other produce (e.g., pears, bananas, peaches, potatoes) contain an enzyme (called polyphenol oxidase or tyrosinase) that reacts with oxygen and iron-containing phenols that are also found in the apple. The oxidation reaction basically forms a sort of rust on the surface of the fruit. You see the browning when the fruit is cut or bruised because these actions damage the cells in the fruit, allowing oxygen in the air to react with the enzyme and other chemicals. The reaction can be slowed or prevented by inactivating the enzyme with heat (cooking), reducing the pH on the surface of the fruit (by adding lemon juice or another acid), reducing the amount of available oxygen (by putting cut fruit under water or vacuum packing it), or by adding certain preservative chemicals (like sulfur dioxide). On the other hand, using cutlery that has some corrosion (as is seen with lower quality steel knives) can increase the rate and amount of the browning by making more iron salts available for the reaction.

3. Apples and other produce (e.g., pears, bananas, peaches, potatoes) contain an enzyme (called polyphenol oxidase or tyrosinase) that reacts with oxygen and iron-containing phenols that are also found in the apple. The oxidation reaction basically forms a sort of rust on the surface of the fruit. You see the browning when the fruit is cut or bruised because these actions damage the cells in the fruit, allowing oxygen in the air to react with the enzyme and other chemicals. 

4. When fresh fruits and vegetables are peeled or cut open, the enzyme called polyphenol oxidase (also called tyrosinase) contained in the cells is exposed to and reacts with the oxygen in the air. The reaction that occurs, which is called oxidation, is what turns the fruits and vegetables brown. The bruising seen on some fruit, such as apples and pears, is caused by the same type of reaction. If an apple is damaged by being hit or dropped, the apple's cells in that area are damaged and the enzymes are exposed to the air inside the apple, causing them to turn brown. When preparing fruits and vegetables for use, an anti-browning solution should be used to prevent them from turning brown.

5. When you slice a banana, you damage various cells. If chemical compounds called phenols mix with a certain enzyme, the combination initiates an oxidation reaction with the air. Brown chemicals are the byproducts of the reaction. Many plant products undergo oxidation reactions when cut or bruised. For example, sliced apples, potatoes, avocados, pears, eggplants and mushrooms all turn brown when exposed to air. A common method to minimize browning is to use lemon juice. The acid in lemon juice deforms the enzyme necessary for the oxidation reaction, so the slices won't brown.