I forgot one more option I considered: Even though every ingredient is stored in a different table, I could enforce unique PK across tables. Then I would not need to specify type in the ID. This would mean that I need to lookup every ID to know which tables it belongs in though.

There is no rule you can make the query like: ?vitamin=b12&mineral=ca&mineral=se in this case the query woukd be for B12, calcium and selenium