Use of hydrogen-bonded supramolecular eutectic solvents for eco-friendly extraction of bioactive molecules from Cymbopogon citratus using Box–Behnken design

Deep eutectic solvents (DESs) are evolving as green extraction media in the search for efficient extraction of bioactive compounds. In the current study, four different choline chloride based DESs (eutectics of Choline chloride with ethylene glycol, malic acid, oxalic acid, and tartaric acid) were prepared with their physico-chemical properties and cytotoxicity evaluation. The FT-IR spectra of all solvents showed a very strong and broad band at 3350–3450 cm⁻¹ due to intermolecular hydrogen bonding between choline chloride and hydrogen bond donors. The DESs were employed for the ultrasound-assisted extraction (UAE) of bioactive compounds from Cymbopogon citratus (lemongrass) to signify the extraction efficiency of DESs over aqueous methanol. The optimization of extraction parameters (time, temperature and biomass to solvent ratio) was done using Box–Behnken design (BBD). These solvents have negligible values of cytotoxicity in the range of 3.67 to 10.20%. The extraction yields obtained with DESs were significantly higher than aqueous methanol. The highest quantities of total phenolic contents (TPC) 116 mg GAE/g dry matter, total flavonoids contents (TFC) 98 mg QE/g dry matter and 2,2-diphenyl-1-picrylhydrazyl (DPPH) radical inhibition 95% were assessed with choline chloride/ethylene glycol solvent due to reduced viscosity. The maximum inhibition zones 45 ± 1.2 mm and 40 ± 1.3 mm against bacterial strains S. aureus and E. coli, respectively and 38 ± 1.2 mm and 29 ± 0.5 mm against fungal strains F. solani and A. niger, respectively were observed by choline chloride/ethylene glycol solvent. The DESs have revealed considerable high extraction yield due to extensive hydrogen bonding, which ultimately relates to the higher antioxidant and antimicrobial activities. The developed DESs would be the best alternative for the green and efficient extraction of phenolic compounds from natural sources.