How to Reduce Oxidation in Apples

Sliced apples can be kept from browning.

A tray of sliced fruit makes a colorful and appetizing addition to any table, if the fruits are carefully selected and arranged with an eye to aesthetics. Some popular fruits such as apples and bananas are prone to turning brown once they're peeled and sliced. This doesn't rule them out for use on fruit trays, because the browning reaction is easily prevented. Does this Spark an idea?

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Enzymatic Browning
- The browning reaction that's visible on apples and other fruits is caused by compounds occurring naturally inside the fruit's cells. When the apple's cell walls are damaged by biting or slicing, phenolic compounds in the cells are exposed to the air. An enzyme in the cells, which is normally contained and kept away from the phenolics, is also released and causes the phenolics to react with oxygen in the air. This results in the familiar brown color and soft, mushy texture that will develop if unchecked.
Controlling the Environment
- Browning can be slowed or minimized by controlling the environment around the apples, after they become slices. For example, refrigerating the apples slows browning because the enzymes are less active at temperatures below 40 F, which is the highest operating temperature for a properly-functioning refrigerator. A second technique is to limit the apples' exposure to oxygen, which deprives the reaction of its fuel. The simplest way to do this is by dropping the apples into a bowl of cold water, once they're peeled or sliced. Commercial food processors can seal the apples in a package containing an inert gas such as nitrogen, which achieves the same result.
Acidity
- Many common acids can also short-circuit the browning reaction. The acids have anti-oxidant properties, which simply means they interfere with the oxidation reaction. The most common acid used for this purpose at home is lemon juice, which is inexpensive and widely available. Ascorbic acid and citric acid are also effective. Ascorbic acid is better known as vitamin C, readily available at any department store or pharmacy. To use it, crush one or more tablets and dissolve the powder in water. Citric acid is the active ingredient in the commercial anti-browning products sold at the supermarket.
Process
- The most effective way to prevent apples from browning is to combine all of these techniques. Prepare a bowl large enough to submerge all of your apples. Fill it with cold water and acidify the water with either lemon juice, crushed vitamin C tablets or a commercial fruit-freshening powder. Stir the water to disperse the acid, then add a few ice cubes to reduce the water's temperature. Peel, slice or chop your apples, placing them in the bowl of cold water immediately. Use the apples immediately, refrigerate them in the bowl or drain them thoroughly and package them in an airtight bag for storage.