I just posted an article on Vitamin C on my hub. I don't know how to direct you there, other than using my name.
To your question: 300mg is child's play. I don't care if it is per Liter or per serving. That is just plain tiny.
The problem with most of us is we have a little bit of knowledge and it is usually from the wrong source. Not the one that may actually have done the testing or experimenting or or or....
There is a branch of medicine called orthomolecular medicine. A well established branch, with enough published material to crush anyone's card house.
For anyone advocting that 2 000mg will cause nausea, all I can say is : did you try it?
I take a minimum of 30 000mg per day and have never had nausea, even at 80 000mg. We are a species that does not make our own Vit. C and consequently, on a GOOD day, need the bare minimum of 20 000mg.
I don't think you could drink enough juice, Sammyfiction.