Ultrasound-assisted green hydrophobic deep eutectic solvents extraction of capsanthin from red peppers: optimization, kinetics, stability, and insights into extraction mechanisms

Capsanthin is a widely used natural pigment, but its extraction with traditional solvents suffers from low efficiency and environmental pollution. To address these issues, this study employed ultrasonic-assisted hydrophobic deep eutectic solvent (HDES) to extract capsanthin. The thymol: menthol (molar ratio 1:2) (HDES-3) was selected as the optimum solvent. The extraction process of capsanthin conformed to Fick's second law. FTIR and SEM analyses confirmed that hydrogen bond interactions between HDES components led to its formation. HDES-3 had the most obvious destructive effect on the raw material structure and showed a stronger extraction ability. Density functional theory (DFT) and molecular dynamics (MD) simulations were employed to further explore the interaction between HDES-3 and capsanthin. The main interactions between capsanthin and HDESs were van der Waals forces and hydrogen bonds with van der Waals forces playing the dominant role. Meanwhile, the more stable hydrogen bond between HDES-3 and capsanthin enhances the stability of capsanthin. This study provides an efficient and green alternative to the use of traditional solvents in the extraction of capsanthin.