Light stability and mechanism of monascus pigment under different lights

Application of Monascus pigments in the food industry is hindered by their vulnerability to light, yet the underlying mechanism of their light-induced fading remains unclear. In this study, Monascus pigments sourced from Monascus rice were employed to investigate their stability under distinct light treatments, including visible light, UV light, and sunlight. The research demonstrates a clear connection between the light stability of Monascus pigments and their composition. Among the various light sources, simulated sunlight emerges as the most deleterious to the red Monascus pigment, whereas UV light inflicts greater damage on the yellow Monascus pigment compared to other sources. Employing density functional theory (DFT) and time dependent DFT (TDDFT), we deduced the mechanism of Monascus pigments' photolysis by comparing EHOMO, ELUMO, △E, λmax, and Eλmax of the six original Monascus pigments. The outcomes reveal a distinct photo-stability sequence for different pigments: red Monascus pigment < orange Monascus pigment < yellow Monascus pigment. Furthermore, our study proposes electron transfer from the c = c double bond to the c-c single bond as a component of the photolysis mechanism. This research contributes theoretical and experimental evidence on the photo-stability and mechanisms governing diverse Monascus pigments under various light conditions. These insights are crucial for optimizing the integration of these pigments in the food industry, with implications for packaging and storage considerations.