<SCIENCE ALERT>
Fruit, like all food, is made up of individual "cells" held together into the fruit itself. The cell walls help the fruit keep its shape and texture. Fruit contains a lot of water. When you freeze the fruit, the water freezes, creating ice crystals. Ice crystals are sharp, and rip the cell walls of the fruit. That leaves the fruit without structure, hence, the fruit becomes mushy. Once the damage is done, there is no putting the fruit back together again.
The way to avoid this, when freezing fruit, is to freeze the fruit so fast that the crystals that form are smaller. Smaller crystals mean less cellular damage. Conventional freezing techniques cannot freeze fruit fast enough to minimize the damage. Commercial applications would use a blast freezer, set at 40 degrees below zero. At home, your best bet would be to buy some dry ice. Even using dry ice, it is essential that you store the fruit in the coldest part of your refrigerator (but NOT where they'd freeze!) for a good amount of time before you put them into the dry ice. To get the smallest crystals, you need to temperature conversion to go as fast as possible, and so you want the starting temperature of the unfrozen fruit to be as low as possible.
(Alton Brown did a whole episode on this. You might want to keep an eye on Food TV reruns for it.)
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