IMHO I don't believe there's a "standard" value. For example, your body easily assimilates whey protein isolate. So, in essence you could take a lot a once.
The body takes some time breaking down beef in the digestive tract. So, if you ate "a lot" of beef (say 80g protein at one sitting) it would be like "time-released" into the system.
I've heard people say that the body will "only" assimilate something in the range of 40-50g of protein in one sitting - I just don't believe it.
Anyone else?!?
xcel