Curcumin is the compound responsible for turmeric’s yellow color and its studied anti-inflammatory activity.
Curcumin is the principal curcuminoid in the rhizomes of Curcuma longa, the ginger-family plant commonly called turmeric. It is a bright yellow polyphenol that gives turmeric powder its characteristic golden color and is also used as the food-color additive E100.
Laboratory research has linked curcumin with antioxidant and anti-inflammatory mechanisms, including effects on several cell-signaling pathways. However, this does not mean turmeric or curcumin is a proven treatment for inflammatory disease. Human evidence remains mixed, partly because curcumin is unstable and poorly absorbed; some enhanced-absorption supplements have also been associated with rare liver injuries.
A common mix-up is confusing curcumin with piperine, the pungent compound in black pepper. Piperine is sometimes added to supplements because it can increase curcumin absorption, but it is not what makes turmeric yellow. Saffron is another yellow spice, while capsaicin is the hot compound in chili peppers.