Because apples and pears both oxidize when exposed to air for too long, I recommend slicing them just prior to using them and then soaking them to prevent browning. The best solution to keep the unsightly browning from happening after tossing your salad is to first bathe the fruit slices in a solution of either water and citric acid (or lemon juice) or in plain seltzer water. To make an acid solution, use 1 Tablespoon of either lemon juice or citric acid powder for each cup of water. Drop your slices in the water solution and allow to sit for 3-5 minutes. Drain the water and lightly dab the fruit or place it in a salad spinner to remove excess liquid before tossing in the salad. Alternatively, if you are pre-slicing your fruit, you can put the pieces back together in the shape of the fruit. Use a rubber band to hold it in place so the sliced edges don't touch air, thus preventing the oxidation process. You can also double up and use both the solution and the rubber band trick to keep the fruit in tact for up to 48 hours. Bonus: this also works for packed lunches!