Numerous plants of medicinal value grow on Hainan Island (China). Given the lack of knowledge on the phytochemical and pharmacological properties of Michelia shiluensis Chun and Y. F. Wu (M. shiluensis), the application of natural antioxidants and antimicrobials in the food industry has attracted increasing interest. This study aimed to compare the chemical composition, free-radical-scavenging capacity, and antibiosis of aqueous extracts of the fresh and dried leaves of M. shiluensis. The aqueous extract of the leaves of M. shiluensis was obtained using steam distillation, and its chemical components were separated and identified via gas chromatography–mass spectrometry (GC-MS). The free-radical-scavenging capacity and antibiosis were determined. Further, 28 and 20 compounds were isolated from the fresh leaf aqueous extract of M. shiluensis (MSFLAE) and dried leaf aqueous extract of M. shiluensis (MSDLAE), respectively. The free-radical-scavenging capacity of MSFLAE and MSDLAE was determined by the 2,2-diphenyl-1 picrylhydrazyl (DPPH) method, which was 43.43% and 38.74%, respectively. The scavenging capacity of MSFLAE and MSDLAE determined by the 2,2′-azino-bis (3-ethylbenzothiazoline-6-sulfonate (ABTS)) method was 46.90% and 25.99%, respectively. The iron ion reduction capacity of MSFLAE and MSDLAE was determined by the ferric-reducing antioxidant power (FRAP) method as 94.7 and 62.9 μmol Fe²⁺/L, respectively. This indicated that the two leaf aqueous extracts had a certain free-radical-scavenging capacity, and the capacity of MSFLAE was higher than that of MSDLAE. The antibiosis of the two leaf aqueous extracts on the three foodborne pathogenic bacteria was low, but the antimicrobial effects on Gram-positive bacteria were better than those on Gram-negative bacteria. The antibiosis of MSFLAE on Escherichia coli and Staphylococcus aureus was greater than that of MSDLAE. Finally, MSFLAE and MSDLAE both had certain free-radical-scavenging capacities and antibiosis, confirming that the use of this plant in the research and development of natural antioxidants and antibacterial agents was reasonable. Plant aqueous extracts are an essential source of related phytochemistry and have immense pharmacological potential.

Nymphaea ‘Blue Bird’, a tropical water lily prized for its ornamental appeal, has been less explored as a source of bioactive flavonoids. This study developed an efficient extraction and purification protocol for flavonoids from this plant and compared their distribution and bioactivities across different tissues. Supercritical CO₂ fluid extraction (SFE) proved optimal, yielding 2.56% under conditions of 24.3 MPa, 39 °C, 91 min, and a CO₂ flow rate of 16 L/min. Subsequent purification with HPD500 macroporous resin enhanced flavonoid purity from 3.05% to 11.46%. Among the tissues analyzed, petals contained the highest levels of total flavonoids (6.43 mg/g) and total phenolics (45.71 mg/g), and exhibited the most potent antioxidant (as shown by the lowest EC₅₀ values for ABTS⁺ and DPPH scavenging) and broad-spectrum antibacterial activities (indicated by the lowest MIC and MBC against Staphylococcus aureus, Pseudomonas aeruginosa, Escherichia coli, and Candida albicans). Antibacterial efficacy was generally superior against Gram-positive bacteria. Widely targeted metabolomics identified 560 metabolites, predominantly flavonols and flavonoids. Principal component and cluster analyses revealed tissue-specific metabolite profiles. KEGG enrichment analysis underscored the significance of the flavonoid biosynthetic pathway, and key differential metabolites—such as luteolin, myricetin, taxifolin, and quercetin—were strongly correlated with the observed bioactivities. These results highlight N. ‘Blue Bird’ petals as a promising source of natural antioxidants and antimicrobials, providing a scientific basis for their future functional applications.