Ultrasound-assisted extraction of antioxidant phenolic compounds from Lavandula angustifolia flowers using natural deep eutectic solvents: An experimental design approach

Abstract

In this study, the green extraction of antioxidant phenolic compounds from Lavandula angustifolia was investigated using ultrasound-assisted extraction coupled with natural deep eutectic solvents (NADESs). One variable at a time, fractional factorial design, steepest ascent/descent method, and central composite design were used to optimize the extraction conditions. Eighteen NADESs based on choline chloride, organic acids, and sugars were tested by one variable at a time approach. The NADES composed of choline chloride and glycerol with a molar ratio of 1:2 showed higher extraction performance than other NADESs and benchmark solvents (70 % ethanol and 80 % methanol). After solvent selection, other extraction parameters including ultrasound amplitude (20–100 %), temperature (40–70 °C), time (5–30 min), liquid to solid ratio (10–50 mL/g), and water content in NADES (10–50 %) were screened using fractional factorial design. Subsequently, the steepest ascent/descent method was applied to approach the suitable level of the selected parameters. Finally, response surface methodology was used to determine the optimal extraction conditions. The optimum conditions were ultrasound amplitude of 60 %, temperature of 60 °C, time of 17.5 min, liquid to solid ratio of 31.7 mL/g, and water content in NADES of 33.5 % with the predicted phenolic content of 50.50 mg gallic acid equivalent/g, flavonoid content of 35.79 mg catechin equivalent/g, antioxidant capacity (AC)DPPH of 41.60 mg Trolox equivalent (TE)/g, ACABTS of 77.13 mg TE/g, and ACCUPRAC of 163.33 mg TE/g. Phenolics and volatiles were analyzed by HPLC and GC-MS, respectively. The results showed a sustainable, green, and effective extraction of antioxidant phenolic compounds from L. angustifolia.