Ultrasound‐assisted extraction of quercetin from onion solid wastes

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Summary The extraction of quercetin with aqueous ethanol solutions from onion solid waste under sonication conditions was investigated using rational experimental design methodologies. It was found that the ethanol concentration (40–80%, v/v) and the temperature (40–60 °C) of extraction are the most influential parameters in the recovery yield, whereas pH (2–6), liquid/solid ratio (30–60 mL g−1) and extraction time (15–35 min) do not significantly influence the completeness of the extraction. The optimal extraction conditions were determined to be an ethanol percentage of 59% and extraction temperature of 49 °C, yielding a total quercetin content of 11.08 mg per g dry weight of onion solid waste. An empirical relationship between extraction parameters and the extraction yield was suggested and verified.