Hydroxyl Radical Formation: A Key Mechanism and Regulatory Target in Monascin Photo-Degradation.

Monascin, a yellow azaphilone pigment derived from Monascus fermentation, undergoes significant photo-degradation that limits its applications. This study reveals that free radical formation, particularly hydroxyl radicals (·OH) generated via H2O2 photolysis, is the primary mechanism driving monascin photo-degradation. Dissolved oxygen synergistically accelerates degradation, whereas deoxygenation reduces radical yield by 68% and lowers the degradation to 5%. Enzymatic scavengers confirmed H2O2 as the critical ·OH precursor: catalase reduced radicals by 61% and suppressed degradation to 7%, while superoxide dismutase exhibited moderate effects. Natural antioxidants ascorbic acid and α-lipoic acid (ALA) protected monascin concentration-dependently, with ALA showing superior photo-protection (68% degradation reduction) due to its broad ROS-scavenging capacity. These findings establish H2O2-derived ·OH as the primary destructive species and identify oxygen exclusion, H2O2 decomposition, and radical scavenging as effective photo-stabilization strategies.