Effects of Porphyrin Photosensitizers on Photostability and Bioactivities of Dietary Pigments, Curcumin and β-Carotene

Natural food pigments such as curcumin and β-carotene are valued for their coloring properties and health-promoting bioactivities, including antioxidant and anticancer effects. However, both compounds are susceptible to light-induced degradation, which can compromise their stability and functional integrity. This study investigated changes in the photostability and bioactivity of curcumin and β-carotene under fluorescent light irradiation, focusing on their interactions with the porphyrin photosensitizers zinc protoporphyrin (ZnPP) and protoporphyrin IX (PPIX). Spectral and HPLC analyses revealed significant pigment degradation, with β-carotene exhibiting greater instability than curcumin. ZnPP and PPIX accelerated the bleaching of both pigments in a concentration-dependent manner, with ZnPP consistently showing stronger destabilizing effects. Functional assays further demonstrated that the antioxidant activity of curcumin was altered by light exposure. Co-irradiation with ZnPP or PPIX significantly reduced the scavenging activity of curcumin against DPPH, ABTS, and AAPH radicals. In HCT-116 colon cancer cells, irradiation alone slightly enhanced the cytotoxic activity of curcumin, whereas co-irradiation with ZnPP or PPIX significantly attenuated this effect. These findings indicate that porphyrin photosensitizers accelerate pigment degradation and impair functional properties under light exposure, highlighting the importance of pigment–photosensitizer interactions during food storage and processing.