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When an apple is cut (or bruised), oxygen is introduced into the injured plant tissue. When oxygen is present in cells, polyphenol oxidase (PPO) enzymes in the chloroplasts rapidly oxidize phenolic compounds naturally present in the apple tissues to o-quinones, colorless precursors to brown-colored secondary products. O-quinones then produce the well documented brown color by reacting to form compounds with amino acids or proteins, or they self-assemble to make polymers.
One question that often accompanies yours is, "Why do some apples seem to brown faster than others?"
Well, nearly all plant tissues contain PPO, however, the level of PPO activity and concentration of substrate--here, the phenolic compounds--can vary between varieties of fruits (say, Granny Smith versus Red Delicious). In addition, a tissue's PPO level can vary depending on growing conditions and fruit maturity. One approach the food industry employs to prevent enzymatic browning is to select fruit varieties that are less susceptible to discoloration-either due to lower PPO activity or lower substrate concentration. This approach, however, may not be practical for the home "culinary scientist."
In the home kitchen enzymatic browning can be prevented by either reducing PPO oxidation activity or lowering the amount of substrate to which the enzyme can bind. Coating freshly cut apples in sugar or syrup can reduce oxygen diffusion and thus slow the browning reaction. Lemon or pineapple juices, both of which naturally contain antioxidants, can be used to coat apple slices and slow enzymatic browning. In addition, both fruit juices are acidic and the lower pH that they bring about causes PPO to become less active. Heating can also be used to inactivate PPO enzymes; apples can be blanched in boiling http://wiki.answers.com/topic.cfm?id=waterfor four to five minutes to nearly eliminate PPO activity. (Be warned that cooking will affect the texture of the product.)
Enzymatic browning is not unique to apples. PPO-a mixture of monophenol oxidase and catechol oxidase enzymes-is present in nearly all plant tissues and can also be found in bacteria . In fact, browning by PPO is not always an undesirable reaction; the familiar brown color of tea, coffee and cocoa is developed by PPO enzymatic browning during product processing.
What else can I help you with?
A sliced apple turning brown is exhibiting the ability to react with oxygen a physical property?
The sliced apple turning brown is a chemical change, not a physical property. It is a result of a chemical reaction between the compounds in the apple and oxygen in the air, leading to the formation of new compounds that give the apple its brown color.
Does an apple skin protect the apple from chemical changes?
Not in general. It does protect the flesh of the apple from certain specific chemical changes (such as oxidation) to some extent, by keeping the oxygen away from the flesh. This is why an apple rapidly turns brown when you cut it: the previously protected flesh is now exposed to oxygen in the air.
Ozone turns benzidine paper to which colour?
Ozone turns benzidine paper to a blue color.
Why Furan turns brown on exposure to air?
Furan is prone to oxidation reactions in the presence of air. This oxidation process causes the molecular structure of furan to change, leading to the formation of brown-colored compounds as byproducts. This is why furan turns brown when exposed to air.
What chemical change occurs when a banana peel turns brown in the air?
When a banana peel turns brown in the air, a chemical change called oxidation occurs. This is due to the exposure of enzymes in the banana to oxygen in the air, which causes them to react and produce brown pigments.
What happens when you put an apple in vinegar?
The apple turns brown and loses color.
Why does a peeled banana turn brown?
Because they rot quicker. There's a greater surface area , both the inside and the outside , that is exposed to the air .
What makes apple tree leaves go brown in summer?
the sun burns it and turns brown
Does the color of an apple change the time that it rotts?
Yes, the apple usawly changes color when it rots it turns brown
How long till an apple in air turns brown?
If it is a whole apple it will go rotten after about a week, but if it is cut it will only take a couple hours to go brown
Why does Guacamole turn dark?
It oxidizes and turns brown quickly after exposure to air. To prevent this, lime or lemon juice can be added to avocados after they are peeled.
Can an apple melt?
No, the best you'll get is a heap of ash.
Does air effect if an apple turns brown if so how?
The oxygen in the air causes food to rot.
What happens when a peeled banana turns black?
it stanks
Is darkening of cut apple physical change?
It's a chemical change because the apple is oxidizing. It turns brown, because of the oxygen, hence the word " oxidizing".
When iron is left outside in the weather it turns reddish brown What is happening What type of reaction is this?
Rusting? Oxidation reaction? Chemical reaction
A sliced apple turning brown is exhibiting the ability to react with oxygen a physical property?
The sliced apple turning brown is a chemical change, not a physical property. It is a result of a chemical reaction between the compounds in the apple and oxygen in the air, leading to the formation of new compounds that give the apple its brown color.
