pasturizing won't hurt anything. Tree Top brand juice should not contain 'bad' preservatives.
Citric and ascorbic acid are fine. You really just need to make sure there's no 'sorbate' added.
if all else fails, frozen apple juice concentrate should not have sorbate but I think you'll find some liquid juice that fits the bill. I think when I made it the Hy-Vee store brand fit the bill.
Primary: English Mild
On tap: Pale Ale, Lancelot's Wheat, English Brown Ale, Steam Beer, HoovNuts IPA
Bottled: MOAM, Braggot, Raspberry Melomel, Merlot, Apfelwein, Pyment, Sweet mead, Cabernet
Gal in 2009: 27, Gal in 2010: 34, Gal in 2011: 13, Gal in 2012: 10