Effects of bio-based solvents on bacterioruberin stability and spectroscopic properties

Bacterioruberin is a rare C50 xanthophyll carotenoid with exceptional antioxidant activity and scalable microbial bioproduction, making it a promising candidate for food, pharmaceutical, and biotechnological applications. However, the effect of solvents on its photophysical properties and stability remains poorly understood, limiting insight into its function in natural systems and its development for engineered applications. This study investigates the optical properties and stability of bacterioruberin extracted from Halobacterium salinarum across a series of bio-based solvents. Steady-state absorption, fluorescence, and resonance Raman spectroscopy reveal that solvent refractive index and hydrogen-bonding capacity govern spectral shifts and aggregation. Additionally, the molar extinction coefficient exhibits strong solvent dependence. Fluorescence emission and excitation spectra show deviations from Kasha's rule. Stability studies demonstrated that protic polar solvents provide the highest thermal and photostability, whereas dipolar aprotic and nonpolar solvents promote faster degradation, particularly under illumination. Moreover, micellar encapsulation and removal of co-extracted proteins further improve the stability of bacterioruberin. Collectively, these results advance our understanding of bacterioruberin photophysics and stability and establish a framework for the rational design of solvent environments in bacterioruberin-based technologies.