Insights into Antioxidant Activity and Trace Element Distribution of Aqueous Extract of Silybum marianum Seeds

The purpose of this work is to investigate the binding state of inorganic elements to flavonoid components in aqueous extract of Silybum marianum (SM) seeds, as well as the antioxidant activity of the extract. This study employed reversed-phase high-performance liquid chromatography (RP-HPLC) to separate silymarin flavonoids in boiling water decoction of SM seeds, and collected the post-column effluent in the segments according to the retention time of seven main silymarin flavonoid components. Inductively coupled plasma mass spectrometry (ICP-MS) was subsequently utilized to quantify nine inorganic elements (As, Cd, Co, Cr, Cu, Fe, Mn, Mo, Zn) in the collected HPLC fractions of the decoction. Meanwhile, electron paramagnetic resonance spectroscopy (EPR) was employed to assess the free radical scavenging activity of aqueous extract of SM seeds, using the signal intensity changes of 2,2-diphenyl-1-picrylhydrazyl (DPPH) and DMPO-OH• adducts as quantitative metrics. The results showed that essential trace elements (Cu, Fe, Mn, Zn) mainly existed as inorganic ions or strong polar forms in the tea-like infusion, with weak binding to flavonoid compounds. On the other hand, the aqueous extract exhibited significant •OH scavenging capacity, with a scavenging rate of 95% against •OH generated by continuous 5 min ultraviolet irradiation of H2O2 aqueous solution. This study provides experimental evidence for the development of SM as a food–medicine dual-purpose resource, proposing that consumption of SM seed tea represents a facile and effective approach to supplement trace elements and intake silymarin for enhancing endogenous antioxidant defense.