Integrated phytochemical profiling and Keap1-targeted computational insights into antioxidant compounds from Camellia longii flower extracts

This study comprehensively investigated the antioxidant activity, phytochemical composition, and potential molecular mechanisms of Camellia longii flower extracts. Among ethanol crude and four fractional extracts, the ethyl acetate extract exhibited the highest total phenolic (774.30 ± 32.15 mg GAE/g DW), flavonoid (278.72 ± 20.24 mg CAE/g DW), and saponin contents (65.62±0.87 mg OAE/g DW). Consistently, the extract also showed the strongest antioxidant activities, with IC 50 values of 3.13 µg/mL (DPPH), 6.10 µg/mL (ABTS), and 0.59 µg/mL (MDA), and an EC 50 of 7.57 µg/mL (FRAP). In addition, the Pearson correlation revealed strong negative relationships between phenolic and flavonoid contents and IC₅₀ values (r = −0.81 to −0.91, p < 0.1), indicating the key role of phenolic compounds in antioxidant activity. UPLC–QTOF–MS/MS analysis identified 90 compounds, 40 of the 90 compounds belong to flavonoids and phenolic compounds. Subsequently, machine learning and molecular docking were used to screen for potential Keap1–Nrf2 inhibitors. Interestingly, six flavonoids were predicted to be active, with strong binding affinities (−8.8 to −10.0 kcal/mol) to key residues (Arg380, Arg415, Arg483) of Keap1. These findings suggest dual antioxidant actions involving direct free-radical scavenging and potential modulation of the Keap1–Nrf2 antioxidant pathway.