Shedding light on curcumin stability.

The stability of molecular curcumin (purcumin, 1a) in solution is strongly light-dependent. Under laboratory artificial light, a relative stability is observed only at neutral pH, while more intense light and/or solar light can trigger degradation via a combination of hydrolytic and oxidative fragmentation of the heptadiendione moiety. Minor curcuminoids in commercial curcumin (purcuminoids) can improve the stability of molecular curcumin, but only under conditions of low irradiation. While confirming earlier observations alerting to the instability of purcumin, our results provide new rationales for unexplained differences between previous studies, question the biological relevance of a non-enzymatic degradation for the bioactivity profiles that have been reported for purcumin, and highlight the need of a better characterization of the degradation of purcuminoids under visible light irradiation.