Optimizing Antioxidant and Biological Activities of Quercus Fructus: Synergistic Role of Inner Shell and Extraction Methods

This study comprehensively evaluated how the inclusion of the inner shell and the choice of extraction method influence the antioxidant activity of Quercus Fructus (QF). Eight QF extracts were prepared with or without the inner shell using stirring (S) and ultrasonication (U) with 80% ethanol, boiled water (B) and autoclave (A) with distilled water. Among them, the ultrasonication extract with inner shell (IU) exhibited the highest antioxidant capacity, showing strong DPPH radical scavenging (228.8 mg TEAC/g), ABTS activity (162.9 mg TEAC/g), reducing power (380.9 mg TERP/g), and SOD-like activity (38.1%). HPLC-UV profiling identified quercetin-7-glucoside (Q7G) as a major detectable compound, although several polar phenolics remained unidentified. In LPS-stimulated Raw 264.7 cells, IU significantly suppressed nitric oxide production and iNOS expression without cytotoxicity. Additionally, IU treatment markedly reduced ROS accumulation in H2O2-exposed zebrafish embryos. These findings suggest that including the inner shell with ultrasonication extraction synergistically enhances QF’s antioxidant efficacy, suggesting a practical strategy for maximizing the functional potential of QF in natural antioxidant development.