thanks..it's in a lot of "prepared" food too...
Oral ingestion compared to inhalation are two totally different games. We know that oral ingestion is fine, as diacetyl is a naturally occurring chemical. The issue is, there is only a limited amount of research done on the inhalation of diacetyl.
I generally try to avoid juices that may contain any form of diketones in them, but can't lie: I have a bottle of Cheesecake from Nicoticket (I don't think you can achieve cheesecake without some diketones) and a bottle of Cuttwood Sugar Bear (which just tastes too good to be "true" -- its gotta have some sort of vanilla/custard/cream flavoring in it). I try and limit the amount of diketones I inhale, just because I don't want to find out, in 20 years, that my decision to vape vanilla custard has some dire negative health effect.