A freshly-cut apple turns brown, a bicycle fender becomes rusty and a copper penny suddenly turns green. What do all of these events have in common?
They are all examples of a process called oxidation.
In technical terms oxidation can be simply defined as the process which involves loss of one or more electron, when various substances react or interact with each other. So according to new definition, involvement of oxygen is not a must for oxidation reaction. Exactly opposite to the reaction of oxidation one more process occurs, which is called reduction, in which addition of electron takes place.
When it involves oxygen, the process of oxidation depends on the amount of oxygen present in the air and the nature of the material it touches. True oxidation happens on a molecular level — we only see the large-scale effects as the oxygen causes free radicals on the surface to break away. In the case of fresh fruit, the skin usually provides a barrier against oxidation. This is why most fruits and vegetables arrive in good condition at the grocery store. Once the skin has been broken, however, the individual cells come in direct contact with air and the oxygen molecules start burning them. The result is a form of rust we see as brownish spots or blemishes.
Oxidation may also be linked with the effects of aging in humans, as well as with other conditions such as cancer, hardening of the arteries, and rheumatoid arthritis. It appears that oxygen molecules and other oxidizing agents, always hungry for electrons, extract these from the membranes in human cells. Over time, this can cause a gradual breakdown in the body's immune system.
To forestall the effects of oxidation, some doctors and scientists recommend antioxidants—natural reducing agents such as vitamin C and vitamin E. The vitamin C in lemon juice can be used to prevent oxidizing on the cut surface of an apple, to keep it from turning brown. Perhaps, some experts maintain, natural reducing agents can also slow the pace of oxidation in the human body.
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