Curcumin is the principal curcuminoid of the popular Indian spice turmeric, which is a member of the ginger family. 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 structure and two equivalent enol forms. The enol form is more energetically stable in the solid phase and in solution.
A curcuminoid is a curcumin or a derivative of a curcumin with different chemical groups that have been formed to increase the solubility of curcumins and make them suitable for drug formulation. These compounds are natural phenols and produce a pronounced yellow color. Many curcumin characters are unsuitable for use as drugs by themselves. They have poor solubility in water at acidic and physiological pH, and also hydrolyze rapidly in alkaline solutions.