Pectic enzymes and the polysaccharide that they break down, pectin, are naturally occurring in apples. To get them to break down your apples for juice, though, you would need to wait for the fruit to ripen to the brink of rotting.
In your example, you would need to add pectic enzymes to the apples. The enzymes will break down the pectin and probably other polysaccharides that are holding the apples' cells together. Freezing will help things along as the ice's expansion will help burst cell walls. You would definitely need to warm the mixture up, though. I'm not familiar with any enzymes that work well while frozen.