Curcumin is the principal curcuminoid of the popular Indian spice turmeric, which is a member of the ginger family (Zingiberaceae). Turmeric's other two curcuminoids are desmethoxycurcumin and bis-desmethoxycurcumin. The curcuminoids are natural phenols that are responsible for the yellow color of turmeric. Curcumin can exist in several tautomeric forms, including a 1,3-diketo form and two equivalent enol forms. The enol form is more energetically stable in the solid phase and in solution.Curcumin can be used for boron quantification in the curcumin method. It reacts with boric acid to form a red-colored compound, rosocyanine.Curcumin is brightly yellow colored and may be used as a food coloring. As a food additive, its E number is E100.