Boosting the essential oil yield of Coriandrum sativum L. using choline chloride-based NADES: an optimized and systematic study employing response surface methodology (RSM)

Coriander essential oil (CEO) is one of the most versatile and powerful essential oils used in the food and pharmaceutical industries, thanks to its numerous properties. Different choline chloride-based natural deep eutectic solvents (NADES) were studied as additives in the hydrodistillation preparation of CEO, and most were able to increase oil yield compared to conventional hydrodistillation. Among these different NADES, the use of choline chloride (ChCl)-urea (N11) led to a yield increase of up to 31.5% in comparison to traditional water hydrodistillation. Few differences were observed in the composition of the oils, except in those prepared using acidic ChCl-citric acid NADES, which led to a significant variation in the CEO composition. The phytochemical profile of CEOs was investigated, and the enantiomeric fractions (EFs) of the most important monoterpene alcohol, linalool, were determined. No differences in the EFs were observed for all the CEOs (86.77% (S)-(+) enantiomer), except for those obtained by using choline ChCl-citric acid (59.26% (S)-(+) enantiomer). Subsequently, a three-level custom design (CD) was used to study the influence of four independent variables: plant-to-N11 ratio, pre-treatment temperature, pre-treatment time, and water percentage. The response surface methodology (RSM) was used to evaluate and optimize the effects of the chosen factors. The RSM results show that the plant-to-N11 ratio, pre-treatment temperature, and water percentage were highly significant in influencing the extraction yield, while the pre-treatment time was not a significant influence. The highest extraction efficiency was obtained using N11 in a 1:4 (w/w) plant-to-NADES ratio, 40 °C and 30 min US-assisted pre-treatment, and 30% (w/w) water content, resulting in an additional 26.6% increase compared with the screening phase. Overall, using the optimized conditions, we were able to enhance the extraction yield up to a total of a 63% (0.77 ± 0.04% (CEOref) vs. 1.10 ± 0.09% (CEOopt)).