Antioxidative and Antimicrobial Activities of Ethanol and Hot-Water Extracts from Quercus acuta

Acorns of the Quercus species are rich in tannins, but their phytochemistry remains insufficiently characterized. This study provides characterization of the antioxidative and antimicrobial activities of twelve phenolic compounds, including gallic acid and catechin, extracted with ethanol and hot-water from evergreen oak Quercus acuta. Samples collected from mature trees were pooled to minimize variation. Extracts were prepared from leaves, branches, pericarps, and kernels. Antioxidant capacity was evaluated using DPPH and ABTS⁺ assays, while antimicrobial activity was assessed against Escherichia coli, Pseudomonas aeruginosa, and Staphylococcus aureus. Kernel ethanol extracts showed the highest antioxidant activity, exhibiting 76% DPPH and 59% ABTS⁺ scavenging at 25 µg/mL, and demonstrated selective inhibition against P. aeruginosa. Ethanol extracts contained higher levels of polyphenols, flavonoids, and tannins than hot-water extracts; kernels showed the highest flavonoid and tannin contents, whereas leaves were rich in catechin. HPLC-MS/MS analysis identified twelve phenolic compounds, with gallic acid being most abundant in kernel ethanol extracts. Principal component and correlation analysis revealed distinct distribution patterns of phenolic compounds among plant parts and a strong positive association between gallic acid content and both antioxidative and antimicrobial activities. Overall, Q. acuta kernels represent a rich source of bioactive phenolics with potential antioxidative and antimicrobial applications.