There are enzymes (polyphenol oxidase & tyrosinase) that react with iron-containing molecules present in the fruit once exposed to oxygen. (It is the iron being involved that causes the brown color just like in metals that oxidize to make brown rust.) This is why cutting the fruit increases the rate of browning. Many cells are ruptured to spill their contents. The contents, including the enzymes and iron bearing molecules, are exposed to the air’s oxygen. The enzymatic reaction with iron doesn’t happen in the intact cell because most oxygen is excluded.
Enzymes are proteins that can be denatured by changes in pH or heat. This is why adding lemon juice or cooking slows or prevents the browning. Adding the fruit to ice water will slow the reaction rate but not stop it.
The other way fruit browns is called a maillard reaction. This one involves a protein that is not an enzyme and a sugar, but requires heat for the change to occur. This is a problem encountered in heating fruit that has been juiced and needs to be pasteurized to be sold.
Apples turn brown due to the release of Ethylene gas from the fruit itself. This is typically triggered by the picking of the unripe apple. Someone had mentioned Carbon Dioxide, which is a gas that actually prevents the fruit from ripening. Industry bathes unripened fruit in carbon dioxide to prevent ripening before the fruit arrives at the market.
The saying that "one rotten apple ruins the bunch" is because the over ripe apple is releasing much more ethylene than its counterparts, thus accelerating their ripening. The same can be seen when a person adds a ripe banana to a bag of unripened fruit to accelerate the process.
Apples as well as other starchy foods like potatoes turn brown due to oxidation of the starches. Oxygen binds to the starches causing the discoloration.
If you are prepairing apples and potatoes you can prevent the oxidation by soaking the sliced pieces in water and a little mild acid for 20 minutes or so. I prefer using lemon juice for that. Works great preventing fresh cut french fries and hash brown from turning that disgusting brown grey color while cooking.
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There are enzymes (polyphenol oxidase & tyrosinase) that react with iron-containing molecules present in the fruit once exposed to oxygen. (It is the iron being involved that causes the brown color just like in metals that oxidize to make brown rust.) This is why cutting the fruit increases the rate of browning. Many cells are ruptured to spill their contents. The contents, including the enzymes and iron bearing molecules, are exposed to the air’s oxygen. The enzymatic reaction with iron doesn’t happen in the intact cell because most oxygen is excluded.
Enzymes are proteins that can be denatured by changes in pH or heat. This is why adding lemon juice or cooking slows or prevents the browning. Adding the fruit to ice water will slow the reaction rate but not stop it.
http://chemistry.about.com/od/chemistryfaqs/f/brow...
The other way fruit browns is called a maillard reaction. This one involves a protein that is not an enzyme and a sugar, but requires heat for the change to occur. This is a problem encountered in heating fruit that has been juiced and needs to be pasteurized to be sold.
http://www.okyanusbilgiambari.com/Bilim/Okyanus-Br...
Apples turn brown due to the release of Ethylene gas from the fruit itself. This is typically triggered by the picking of the unripe apple. Someone had mentioned Carbon Dioxide, which is a gas that actually prevents the fruit from ripening. Industry bathes unripened fruit in carbon dioxide to prevent ripening before the fruit arrives at the market.
The saying that "one rotten apple ruins the bunch" is because the over ripe apple is releasing much more ethylene than its counterparts, thus accelerating their ripening. The same can be seen when a person adds a ripe banana to a bag of unripened fruit to accelerate the process.
Apples as well as other starchy foods like potatoes turn brown due to oxidation of the starches. Oxygen binds to the starches causing the discoloration.
If you are prepairing apples and potatoes you can prevent the oxidation by soaking the sliced pieces in water and a little mild acid for 20 minutes or so. I prefer using lemon juice for that. Works great preventing fresh cut french fries and hash brown from turning that disgusting brown grey color while cooking.
Carbon dioxide turns the apple brown... Part of the decomposition process.
exposed to oxygen