An apple starts turning brown quickly once it is cut and exposed to oxygen. This browning process is called oxidation. Brown apples don't look appealing to me, especially in a salad. What I use to stop my apples from oxidizing can be found in almost every kitchen.
1/2 tsp salt
Ice cold water
Cut the apple. I was recently given an apple cutter by my husband, it makes cutting an apple so much easier. I really enjoy using it.
Put a cup of very cold water in a small bowl with half a teaspoon of salt. Once the apple is cut, put it in the water for 5 minutes. Take the apple slices out of the water and rinse with water.
Other ways of preventing oxidation is by soaking them in lemon water, sprite, lime water etc.