Fruit oxidation is the result of cell damage in thin skin fruits such as apples, peaches, pears and bananas. Oxidation starts when peeling, slicing or rough handling causes cell membranes within the fruit to rupture and release an enzyme called polyphenoloxidase. The characteristic brown color that develops on the surface of the fruit is an organic compound that forms when polyphenoloxidase mixes with oxygen. While you cannot prevent fruit oxidation from ever occurring, you can buy time by giving oxygen something else to work on before it starts working on your fruit.
Brush smaller pieces of sliced fruit, such as bananas, with lemon-lime soda, or lemon, lime, orange or grapefruit juice. Oxygen will first turn its attention to the citric acid in the soda or juice as it undergoes oxidation at a faster rate than your fruit.
Soak whole or large slices of fruit, except for bananas, for up to 15 minutes in mixing bowl that contains a solution of 1/4 cup citrus juice or cider vinegar and 1 qt. of cold water. This mixture works by making the surface of the fruit less acid and by allowing less oxygen to mix with the fruit slices.
Crush a 500 mg tablet of vitamin C and let it dissolve in 1 gallon of water before adding sliced fruit. Ascorbic acid, a component in vitamin C, will stop oxidation from occurring. This method is a good choice when you are slicing large amounts of fruit, as it will not affect taste.
Always handle thin skin fruit with care. Rough handling or dropping a piece of fruit can cause small tears in the skin and start the process of oxidation.