Determination of phenolic acids in Prunella vulgaris L.: a safe and green extraction method using alcohol-based deep eutectic solvents

The extraction of natural products with available green and safe solvents is rather limited. Recently, deep eutectic solvents (DESs) have attracted growing interest as sustainable and safe solvents. However, few studies have applied DESs in the extraction and determination of phenolic acids. Therefore, in the present study, DESs (alcohol-based) were applied to extract rosmarinic acid and salviaflaside, which were the predominant phenolic acids in Prunella vulgaris. The extraction yield acted as the comprehensive evaluation index, and a central composite design (CCD) of the response surface liquid/solid ratio methodology (RSM) was employed to further optimize the alcohol-based DES extraction conditions. The results showed that the optimized extraction conditions included a water/DES ratio of 36% (v/v), liquid/solid ratio of 14 mL g(-1), extraction temperature of 86 degrees C and extraction time of 46 min for rosmarinic acid as well as a water/DES ratio of 30% (v/v), liquid/solid ratio of 12 mL g(-1), extraction temperature of 89 degrees C and extraction time of 32 min for salviaflaside in ChCl/ethylene glycol at 1/4 ratio. Under these conditions, the mean experimental value of the extraction yields (3.658 and 1.049 mg g(-1) for rosmarinic acid and salviaflaside) corresponded well with the predicted values. Moreover, these experimental values were higher and safer than those obtained from previously reported conventional extraction methods. This study suggests that DESs can be utilized as sustainable and safe extraction media for natural products.