Study on the Antibacterial, Anti-inflammatory, and Antioxidant Effects of Alnus firma Leaf Extracts via Different Extraction Methods

This study explores the antibacterial, anti-inflammatory, and antioxidant properties of hot water extract, ethanol extract, and fermented products derived from the leaves of Alnus firma, a plant native to Jeju Island, with the aim of developing materials for skin health applications. Antibacterial activity was assessed against skin-harmful pathogenic bacteria, including Staphylococcus aureus, Pseudomonas aeruginosa, Corynebacterium diphtheriae, Streptococcus pyogenes, Acinetobacter junii, Cutibacterium acnes, and Stenotrophomonas maltophilia, using the disk diffusion method. Anti-inflammatory effects were evaluated through nitric oxide (NO) production inhibition assays, while antioxidant activities were measured using DPPH and ABTS assays. Among the tested samples, the ethanol extract exhibited the strongest antibacterial activity against C. acnes, A. junii, and S. maltophilia. Although the hot water and ethanol extracts showed limited anti-inflammatory effects, the fermented product demonstrated significant activity. All three samples exhibited high antioxidant activity. These findings suggest that A. firma leaves hold significant potential as effective ingredients for skin health products. Notably, the ethanol extract stands out as a promising candidate for cosmetic applications due to its potent antibacterial and antioxidant properties.