Eco-friendly and high-efficient extraction of natural antioxidants from Polygonum aviculare leaves using tailor-made deep eutectic solvents as extractants

Abstract

Herein, an eco-friendly deep eutectic solvents-based ultrasonic-assisted extraction (DES-based UAE) procedure was exploited for high efficient extraction of natural antioxidants from Polygonum aviculare leaves (PALs). Choline chloride-levulinic acid (ChCl-Lev) was adopted for the first time as extractants for further optimization. Based on the results of single-factor experiments, the optimal extraction conditions for simultaneously maximizing the TPC, TFC and antioxidant activities were obtained by response surface methodology (RSM). RSM results indicated that four independent variables had evident effects on all responses, while ultrasonic temperature and liquid to solid ratio (L/S) showed significant interaction effects on the TFC and FRAP. Under the optimal conditions (L/S of 85:1, ultrasonic time of 60 min, ultrasonic temperature of 70 °C and water content in DES of 38%), the corresponding responses resulted in: TPC-102.07 ± 2.51 mg GAE/g DW, TFC-69.43 ± 9.37 mg RE/g DW, DPPH•-315.26 ± 7.52 μmol TE/g DW, and FRAP-496.79 ± 6.38 mM Fe(Ⅱ)SE/g DW. The measured results were consistent with the predicted values. Moreover, a comparative study showed that the ChCl-Lev-based UAE resulted in higher TPC, TFC and antioxidant activities than other available extraction methods. HPLC-DAD analysis results showed that ChCl-Lev-based UAE yielded high levels of antioxidants including gallic acid (39.80 mg/g DW), 5-caffeoylquinic acid (11.83 mg/g DW), myricitrin (10.47 mg/g DW), 3′′-O-galloylmyricitrin (7.91 mg/g DW), 3-chlorogenic acid (7.16 mg/g DW), quercitrin (4.26 mg/g DW), and avicularin (3.02 mg/g DW). This study develops an eco-friendly and high-efficient ChCl-Lev-based UAE method to obtain extracts rich in natural antioxidants from medicinal plants, which can be well applied in food, cosmetic and pharmaceutical industries.