Novel mechanism of enhancing Arthrospira chlorophyll photostability by natural deep eutectic solvent: Axial coordination between betaine-xylitol and the porphyrin ring.

Chlorophyll (Chl) extraction from Arthrospira using conventional organic solvents is limited by toxicity, environmental concerns, and poor pigment stability. Here, natural deep eutectic solvents (NADES) were explored as green media for Chl extraction and stabilization. Among eight screened NADES systems, betaine-xylitol (Bet-Xyl) showed the best extraction efficiency and photostability. Under continuous illumination (19,200 lx) for 6 h, Chl extracted with Bet-Xyl exhibited a retention rate of 90.61 ± 2.61 %, significantly higher than that obtained with conventional solvents. Futher process optimization through single-factor experiments achieved a Chl yield of 65.06 ± 4.57 %. The results based on the results of quantum chemistry revealed that Bet-Xyl interacts with Chl through hydrogen bonding and axial coordination with Mg in the porphyrin ring, thereby stabilizing the pigment structure. Overall, this study demonstrates the potential of Bet-Xyl as sustainable extraction media for Chl while providing mechanistic insights into the stabilization of natural pigments.