Synthesis of tunable hydrophilic deep eutectic solvent for the extraction of antioxidants from Salvia officinalis L.

Abstract

The leaves of Salvia officinalis L., a plant known for its high antioxidant content, were selected as the focus of this research. This research aimed to evaluate the antioxidant activity of sage leaves extract by varying the hydrophilic deep eutectic solvents (DESs) compositions and molar ratios. The hydrophilic DESs were synthesized using the heating method with diverse combinations of DES, including lactic acid (LA), oxalic acid (OA), succinic acid (SA), and ethylene glycol (EG) as hydrogen bond donors (HBDs) and choline chloride (ChCl) as the sole hydrogen bond acceptor (HBA) with varied molar ratios of HBA to HBD (1:1, 1:2, and 2:1). The antioxidants were extracted using ultrasound-assisted extraction method at 70°C of extraction temperature, 30 mins of sonication time, and 1:30 g/mL of solid-solvent ratio. The DES extraction efficiency was evaluated based on the antioxidant scavenging abilities measured by α, α-diphenyl-β-picrylhydrazyl (DPPH) free radical scavenging assay. The results revealed that the ChCl-OA showed the highest antioxidant activity (67.660 μg/mL), followed by ChCl-EG (52.327 μg/mL) and ChCl-LA (33.116 μg/mL) with molar ratios of 1:1, 1:2 and 1:2, respectively. As conclusion, ChCl-OA with molar ratio of 1:1 exhibited the highest extraction efficiency (77.259%) as compared to the other DES combinations using 70% of methanol (v/v).