Definition of "adulterant"

With regard to the presence of opium in ale, it appears to form a very deleterious adulterant;

1817 May 1, “Collectanea Dietetica”, in The Monthly Magazine, volume 43, number 297, page 320

Potato-flour is the waste of potato after the starch and alcohol have been extracted; it has no more food value than so much wood, and as its use as a food adulterant is a penal offence in Europe, thousands of tons of it are shipped to America every year.

1906, Upton Sinclair, chapter 11, in The Jungle‎, New York: Grosset & Dunlap, page 139

Once upon a time not so long ago, most of those chemical additives would have been deemed “adulterants” by the Food and Drug Administration. But after an all-out campaign of lobbying by the baking industry in the 1950s, the FDA liberalized its “standard of identity” for bread, permitting bakeries to add dozens of new additives to what had previously been a simple two- or three-ingredient food.

2013, Michael Pollan, Cooked: A Natural History of Transformation‎, Part 3, p. 268