Relational Design - Multiple tables into one foreign key column?
I think you are looking for a subtype/supertype construct.  Meat would be your migrating key and would contain a Type field that indicates which sub-type of meat it relates to.  So:

PurchaseMeat = Meat = {MeatBeef, MeatPork, MeatPoultry}

Where Meat is the type and the key of the subtype.

In Crow's feet notation this is a circle with a line under it.