An overview of carotenoid extractions using green solvents assisted by Z-isomerization

The wide application of carotenoids in food, cosmetic, and pharmaceutical products due to their bioactive and color properties has emphasized a need for improved methods for their extraction. Recently, “green chemistry” has become a significant focus of research to minimize environmental and health impacts, leading to increased demand for safe and sustainable solvents. Several specific green solvents such as edible oils, supercritical CO2 (SC–CO2), ionic liquids (ILs), deep eutectic solvents (DES) and natural deep eutectic solvents (NDES) have emerged for carotenoid extraction. Efficient extraction processes have been successfully developed by combining these green solvents with novel extraction techniques (such as microwave-assisted extraction, ultrasound-assisted extraction, high-pressure processing and homogenization). Limiting factors (high water content of carotenoid-rich samples; the presence of cell wall/membrane and other physical and chemical barriers; low solubility, high crystallinity, difficult separation, and purification of carotenoids) and new ideas (carotenoid Z-isomerization) for carotenoid extractions are also outlined. Edible oils, biocompatible ILs (Bio-ILs) and NDES with little or no toxic effects are promising for carotenoid extraction. Alterations in the physicochemical properties of carotenoids by Z-isomerization are beneficial for their extraction. Toxicological studies about green solvents, especially for hydrophobic NDES, are urgently needed. More studies on green solvents (especially Bio-ILs and NDES) and post-extraction purification of carotenoids from the extracts are needed.