Chapter 9 is again by the priestly author of the first creation story and again he is insisting that vegetables were the only approved food before the flood.
You lost me there--isn't the vegetable sacrifice rejected, while the animal sacrifice is approved? How would this cause the reader to conclude that vegetables were the approved food?
Its in priestly post flood story in chapt 9 that God is said to give flesh as food as he had earlier given vegetation. Notice that blood is the issue
3 "Every moving thing that is alive shall be food for you; I give all to you, (B) as I gave the green plant.
4 "Only you shall not eat flesh with its life, that is, (C) its blood.