Sugar-based natural deep eutectic solvent ultrasound-assisted extraction for the determination of polyphenolic compounds from various botanical sources

In this study, a novel ultrasound-assisted extraction method utilizing natural deep eutectic solvent (NADES) was developed for the efficient extraction of 20 polyphenolic compounds from various botanical sources, followed by HPLC–DAD detection. By mixing choline chloride as a hydrogen bond acceptor (HBA) and various sugars, such as arabinose, fructose, galactose, trehalose and raffinose, as well as one sugar alcohol (mannitol), in a range of molar ratios, 21 different DESs were prepared and tested. The important parameters influencing the extraction efficiency were studied and optimized using the one-variable-at-a-time (OVAT) method on Picea abies (L.) Karst. needles as a model sample. The optimal conditions were found to be NADES formed by mixing choline chloride and raffinose in a 1:1 M ratio containing 30% water, extraction temperature 25 °C, extraction time 30 min, ultrasound power 60%. The calibration plots were linear from 0.50 to 50 μg mL−1 from standard for the majority of the target analytes, and the instrumental LOD and LOQ values were found to be in the range 0.02–0.19 μg mL−1 and 0.07–0.64 μg mL−1, respectively. The extraction efficiency of the NADES was compared with the efficiency of classical solvents, such as water or methanol, and the NADES revealed a remarkable increase of extraction yield. The newly developed extraction method was successfully applied for the analysis of diverse range of plant materials, encompassing coniferous plants such as Picea abies (L.) Karst, Pinus sylvestris L., and leafy trees Quercus robur L., Ulmus glabra Hudson and Brassica napus L. thereby revealing the polyphenolic profiles of different botanical species.