Ammonium fumarate is a compound with formula (NH4)2(C2H2(COO)2). It is the ammonium salt of fumaric acid. As a food additive, it has the E number E368. Ammonium fumarate is a compound with formula (NH4)2(C2H2(COO)2). It is the ammonium salt of fumaric acid. As a food additive, it has the E number E368.