Simple and green method for the extraction of xanthohumol from spent hops using deep eutectic solvents

Spent hops (SH) are a rich source of the prenylated chalcone, xanthohumol (XN), which has a broad spectrum of biological activity. In this study, four choline chloride-based deep eutectic solvents (DESs), which contained glycerol, ethylene glycol, propylene glycol, or lactic acid as a hydrogen bond donor, were tested for the extraction of XN from SH. XN-rich precipitates were obtained by the addition of water (as an antisolvent) to the DES extracts. To determine the XN contents, the precipitates were extracted with methanol and then analyzed by HPLC. The highest XN extraction yield (2.30 mg/g SH) was obtained using a DES composed of choline chloride and propylene glycol (1:2 mol/mol) with 5 wt% water, 1:50 SH/DES (w/w), and 3:1 antisolvent/DES (v/w) at 60 degrees C for 1 h. This DES could be recovered and reused at least three times without significantly decreasing the XN extraction yield. Our results therefore demonstrated that DESs can be considered green, efficient, and promising solvents for the extraction of XN from SH. Moreover, the proposed simple DES-based method appears to be an effective alternative to conventional XN extraction methods.