How to Prevent Apples from turning Brown
The fast food chains that sell pre-cut apples in bags use Nitrogen or similar food inert gas. But I can't see this being practical in a normal kitchen

Acid is the answer, try slightly less noticeable acid sources such as fresh (as in you squeezed it) orange or pineapple juice

They should not taint the taste so much if you just lightly brush it on the exposed surfaces, don't soak the apples in it