- When an apple is cut into or is bruised, the result is brown flesh. This browning is caused by the introduction of oxygen into the delicate plant cells. It is called oxidation.
- When the chloroplast cells (replete with polyphenol oxidase enzymes) oxidize from an injury, phenolic compounds starts to produce o-quinones in the apple's flesh. Although o-quinones are colorless, they are the first step in the reaction of the amino acids that produce a brown compound.
- Fruit maturity and different growing conditions can effect the browning of an apple. Granny Smith and Red Delicious apples brown very quickly when they are very ripe.
- Toss the cut apple slices in sugar or a syrup to reduce the oxidizing of the apple flesh. Both pineapple and lemon juice contain high levels of antioxidants that can slow the enzymatic browning of the cut apple. Lemon or pineapple juices, both of which naturally contain antioxidants, can be used to coat apple slices and slow enzymatic browning. You can also heat the apples to slow the browning of apple slices. The one challenge of using heat to slow the browning of apples is the heat changes the texture of the apple.
