Green and efficient extraction of wormwood essential oil using natural deep eutectic solvent: Process optimization and compositional analysis

Various natural deep eutectic solvents (NaDESs) were synthesized and coupled with steam distillation to extract wormwood essential oil. Structural (Fourier-transform infrared) and physical (pH, conductivity, differential scanning calorimetry) characterizations of the DESs were performed. The binding sites, types and intensity of interaction forces of the NaDESs were analyzed using quantum chemical calculation. Wormwood essential oil was collected using NaDES-coupled steam distillation. The yield of essential oil was calculated according to the amount of essential oil collected. The types and area percentages of the peaks of the main active substances were analyzed using gas chromatography-mass spectrometry. Among the prepared NaDESs, l-carnitine-malic acid DES afforded the highest yield and the most active substance types (area percentage ≥ 2 %); the process was superior to steam distillation coupled with water, NaCl, and cellulase. Single-factor experiments showed that the distillation efficiency was optimal with a DES concentration of 50 wt%, solid–liquid mass ratio of 1:6, and distillation time of 10 h. Scanning electron microscopy was used to further explore the extraction mechanism. The structure of the plant cell wall was most severely damaged by l-carnitine-malic acid DES, which increased the extraction efficiency and the types of active substances (area percentage ≥ 2 %). Therefore, NaDES-coupled steam distillation is an efficient, green, feasible, and innovative method for extracting wormwood essential oil.