Sustainable ultrasound-assisted extraction of valuable phenolics from inflorescences of Helichrysum arenarium L. using natural deep eutectic solvents

In the present study, an analytical methodology based on natural deep eutectic solvents (NADESs) and ultrasound-assisted extraction (UAE) is demonstrated as an environmentally friendly protocol for the isolation of valuable phenolic compounds from inflorescences of Helichrysum arenarium L. For this purpose, 11 different NADESs containing choline chloride and selected hydrogen bond donors, including organic acids, polyols, sugars and an amide, were tailored and evaluated based on the content of individual compounds determined by HPLC-PDA-MSn. Choline chloride-lactic acid based NADES (NADES 1) showed the most promising extraction efficiencies for flavonoids (15.34 ± 0.10 mg g−1) and phenolic acids (5.10 ± 0.12 mg g−1) as the efficiencies were comparable to those obtained with 80 % methanol (15.60 ± 0.09 mg g−1 and 5.32 ± 0.18 mg g−1, respectively) and up to 54 % higher compared to water (9.94 ± 0.13 mg g−1 and 5.47 ± 0.22 mg g−1). Furthermore, three essential parameters of the proposed NADES 1 methodology (UAE time, water content in NADES, and NADES hydrogen donor/acceptor molar ratio) were optimized by Box-Behnken experimental design. Based on the statistically evaluated results the following conditions were determined to be optimal: an UAE time of 85 min, 38 % water in NADES 1, and a molar ratio of choline chloride:lactic acid of 1:4. The developed approach allows easy transfer of the proposed methodology to large-scale extraction, enabling clean production with minimal environmental impact.