Biorefinery of flavonoid aglycones using acidic natural deep eutectic solvents: Role of Bronsted acids and application in valorization of Sophora japonica buds waste.

Biorefinery of flavonoid aglycones by natural deep eutectic solvents (NADESs) is a green approach for the valorization of agro-food wastes. Using rutin/quercetin as a model system, this work studies the role of Bronsted acids in deglycosylation of flavonoid glycosides and the sustainable approach to producing aglycone-rich extracts by acidic NADESs. Different NADESs were tested, and the effects of Bronsted acids in catalysis and Hammett acidities were determined. The deglycosylation kinetics of rutin in the choline chloride-citric acid was measured and followed a first-order model with a half-life time (t1/2) of 0.16 h at 90 °C and an activation energy (Ea) of 140.3 kJ mol-1. A two-step one-pot approach was valid to produce quercetin-rich extracts from Sophora japonica buds waste. The quercetin-to-rutin ratio in the acidic NADES extracts was adjustable by changing the heating time. The acidic NADES of ChCl-Citric and quercetin-rich extracts showed low cytotoxicity to Caco-2 cells with EC50 greater than 2000 mg L-1, and the cytotoxicity was mainly determined by citric acid. The study provides a new perspective for the valorization of bioproducts into ready-to-use flavonoid aglycone-rich extracts using acidic NADES. [ABSTRACT FROM AUTHOR]