Optimization of polyphenols extraction by deep eutectic solvent from broccoli stem and characterization of their composition and antioxidative effects

Broccoli stem is known to possess abundant polyphenols. To efficiently extract polyphenols from broccoli stems, we herein describe an updated deep eutectic solvent extraction (DESE) method. Response surface modeling was utilized for optimization of the DESE method, achieving the best yield of 5.10 ± 0.04 mg polyphenols/g broccoli stem powder under the following conditions: solvent, choline chloride-urea (molar ratio 1:3); extraction temperature, 80 °C; extraction duration, 55 min; water content, 60%; and liquid-solid ratio, 41:1 mL/g. Ultra Performance Liquid Chromatography-ElectrosprayIonization-Quadrupole Time-of-Flight/Mass Spectrometry (UPLC-ESI-QTOF/MS) was then employed for characterization of the main -composition, which revealed sinapinic acid (5.32%), trans-cinnamic acid (88.8%), quercetin (3.06%) and isochlorogenic acid (2.88%) as the dominant polyphenol compounds, and the extraction mechanism of the high efficiency of DES was dicussed. Moreover, the extracts from (ChCl-urea) DES exhibited remarkable antioxidant activity in vitro antioxidant test. These findings provide a viable and practical approach for broccoli culm polyphenol extraction and analysis, providing a methodological and knowledge basis for recycling broccoli wastes in an eco-friendly fashion.