Preposition?

Refrigerated self-service cabinets keep goods at the required temperatures. These are at zero degree Fahrenheit for frozen food, 28-32 degrees for meat and fish, and 40-50 degrees for dairy produce and provisions.

The sentences are from an article. I'd like to know whether the preposition 'at' in the second sentence can be left out or not. If it cannot be left out, please explain to me.