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
cooking.stackexchange.com/users/3203/TFD
A great place to start is the Scientific American article,
Why do apple slices turn brown after being cut?
The discoloration of apples is caused by oxidation , which, in the case of apples, is actually caused by oxygen (this is not always the case).
Specifically it's caused by an enzyme in the apple caused polyphenol oxidase (PPO).
There are many things you can try if you want to prevent this browning:
First, choose a type of apple that has lower PPO .
Apples classified as "baking" apples tend to be better for this, although that's not always a reliable indicator.
Orin, a Japanese apple, is said to have a mild pineapple flavour and has very low PPO (does not brown easily).
Golden Delicious and Granny Smith are also good in this respect.
Have a look at this annotated list of common apple varieties for more.
The suggestion that most people will give you - to use lemon juice - works for two reasons.
One is that lemons are high in antioxidants, which prevent oxidation as the name implies.
The other is the acidity; lower pH somewhat inhibits oxidation.
So apply this knowledge; if you're concerned about the taste imparted by lemon juice, understand that almost all fruits (except apples) are high in antioxidants and most fruit juices are at least mildly acidic.
Choose something that's closer to the taste of apple, or doesn't clash as much; pineapple, grapefruit, or orange juice might be better bets.
Some spices are also high in antioxidants; if your dessert includes a lot of cinnamon then sprinkle that cinnamon directly onto the apples; it's also a mild antioxidant and will at least slow the browning.
Alternative, you can simply lower the amount of oxygen available by either coating with syrup or placing the apples in a sealed (i.e. tupperware) container, or both.
This should be fine if the apples are intended as a dessert.
Lastly, blanching (boiling)
the apples for 5 minutes will basically kill (inactivate) the PPO enzymes which will totally prevent browning - although it'll obviously also soften the apples a whole lot, so whether or not this is viable depends on exactly how you plan to serve them.
cooking.stackexchange.com/users/41/Aaronut
If you don't want to use lemon or lime juice, you can get a vitamin-c tablet and dissolve it in water.
Same effect, only flavorless.
cooking.stackexchange.com/users/145/Covar
Agree with TFD.
I usually use a bit of lemon juice and mix the juice with cold water.
I think the ratio would be 1 lemon per 1L water.
just dip the apple in the mix for a few seconds and then the apple should last for a long time
cooking.stackexchange.com/users/2951/Foodrules 
You can use acid, such as some lemon juice.
In your baking aisle at the grocery store in the canning area you also may find Ball Fruit Fresh, which provides preservatives.
cooking.stackexchange.com/users/1816/justkt
It depends on how long you need to preserve the apples for.
If it's only between slicing and serving, just submerge the peeled apples in water.
No oxygen, no oxidisation.
Depending on the type of apples you're using, you can keep them submerged for more or less time before they start to get soft & pulpy.
Keeping them in the fridge will extend that time, but not indefinitely.
cooking.stackexchange.com/users/5897/Camassey
I don't prefer to any of above.
Generally people find a way which we can use at glance & easily available at home.
I prevent my apple from turning brown by spraying some salt on it.
And it works for me very well from very long time!
cooking.stackexchange.com/users/14943/Foram Mukund Shah
That is it, you need acid to prevent oxidation.
The only other possibility would be to prevent air getting to your apples, but if you cover them with some mass you'd probably not see the brown color anyway...
cooking.stackexchange.com/users/3144/RBloeth
I love to use Apples in my Desserts. They look really delicious when I just make them, but by the time they are consumed as dessert, the apples have all turned brown. and suddenly the dessert doesn't look all that nice anymore. How do I prevent this?  UPDATE:  I remember reading somewhere that dipping apples in lemon juice prevents the oxidation which turns them brown, but this effects the flavor of my recipe. What else can I do?
How to Prevent Apples from turning Brown
cooking.stackexchange.com
<dessert><apples>
cooking.stackexchange.com/questions/9018
cooking.stackexchange.com/users/3039/Srikar Appalaraju
Baking apples are better at avoiding this, but you can use an acid like lemon or lime juice or a dissolved vitamin C tablet, or just submerge the slices in water before serving. Try a different kind of apple that doesn't oxidise. You can coat with an acid like lemon juice or spray with salt.
Try using baking apples instead. Try coating with lemon juice or any other acid. Put the apples in water. Spray some salt on the apples.