Sulforaphane is an isothiocyanate compound abundant in cruciferous vegetables like broccoli. Studies in cell and animal models have shown this compound’s significant potentials as anticancer, anti-diabetes and anti-autism reagents, and so on. Sulforaphane was reported to act as an indirect antioxidant via activating the Nrf2 pathway. In our preliminary studies, we also observed the excellent free radical clearance capability of carbon dots made from broccoli powder. Therefore, efficient extraction of sulforaphane has raised great interest. However, a green and efficient extraction method is still missing, given dichloromethane has been usually used in sulforaphane extraction from plants. In this study, we investigated the application of deep eutectic solvents (DESs) to extract sulforaphane from broccoli. First, we found that the extraction efficiency of hydrophobic DESs prepared with methyltrioctylammonium chloride and ethylene glycol at a molar ratio of 1:1 was the highest, with 90-97% yield.  After applying methyltrioctylammonium chloride ethylene glycol as the extraction solvent, the factors affecting the extraction efficiency were optimized by response surface analysis, and we found that the optimal extraction conditions were: volumetric ratios of hydrogen bond acceptor (HBA): hydrogen bond donor (HBD) of 1:1, salt concentration of 0.25 g / ml, vortex time of 45s, and DES: water volumetric ratio of 1:1.5. Under these conditions, the extraction yield was 97.7%, which was significantly higher than 70% of the conventional solvent dichloromethane. In addition, sulforaphane was recovered from the DESs by activated carbon separation, with DES reusable. The extraction efficiency of activated carbon was 68.62%. The synthesized DESs were further characterized by <sup>1</sup>H-NMR and FT-IR, and the correlation was found between the extraction efficiency and the solvent polarity. This is the first study reporting that hydrophobic DES was able to efficiently extract of sulforaphane from broccoli, which fits the green and environment-friendly concept as well.

Green and efficient extraction of sulforaphane from broccoli

ACS Spring 2022

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