First ask the breeder what they fed.
I know Great Danes (another giant breed) should never be fed puppy food. I recommend a high quality adult formula food. Canidae is a wonderful food, usually easy to find, and an all life stages food.
www.canidae.com
Some other great foods:
Innova
California Natural
Solid Gold
Timberwolf
Merrick
I would personally stay away from Purnia, Pedigree, Science Diet, Iams, Eukanuba, Kibbles and Bits, Ol Roy, Beneful, Alpo etc