Once you cut into a fruit nothing can completely stop the oxidization process that makes fruit brown from happening.  Fruit oxidizing has nothing to do with whether you pack it in a PlanetBox or not.  However, there are a few things that customers have suggested you can do to slow down the oxidation process.Prepare your fruit as close as possible to when you're planning to serve it.Use a sharp knife. This minimizes the microscopic bruising.Toss the fruit with lemon or lime juice.  The acid in citrus fruits inhibits and slows the chemical reaction that causes oxidization. Blot the fruit on a towel after tossing.There are some powders available that you can sprinkle over fruit to stop it from browning. Most of the powders are made from absorbic acid (Vitamin C) and sugar.