Comparison of the Antioxidant and Antimicrobial Effects of Phytoncide Essential Oils

Background: The potential toxicity of synthetic antioxidants such as butylated hydroxytoluene (BHT) and butylated hydroxyanisole (BHA) and the emergence of antibiotic-resistant microorganisms owing to antibiotic misuse have caused increased interest in natural alternatives. Plant-derived essential oils (EOs), particularly those rich in monoterpene compounds such as α-pinene, limonene, and 1,8-cineole, have been widely reported to exhibit antibacterial, antioxidant, and anti-inflammatory activities through mechanisms including cell membrane disruption and free radical scavenging. This study aimed to investigate the antioxidant and antibacterial effects of 11 plant- derived EOs, including coniferous and herbal species, and explore blending strategies to maximize antibacterial efficacy as a scientific basis for the development of natural functional materials. Methods and Results: Antioxidant activity of 11 EOs and four blending oils (BOs) was evaluated by determining their radical scavenging activity using 2,2-diphenyl-1-picrylhydrazyl (DPPH), elu- cidating the production of intracellular reactive oxygen species (ROS) using 2’,7’-dichlorofluorescin diacetate (DCF-DA), and confirming their cytotoxicity using the 3-(4,5-dimethylthiazol-2- yl)-2,5-diphenyltetrazolium bromide (MTT) assay. Antibacterial activity was assessed against 13 reference strains using paper-disk diffusion, minimum inhibitory concentration (MIC), and minimum bactericidal concentration (MBC). Although EO No. 9 (Hinoki-JP) exhibited the highest antioxidant activity, it showed high cytotoxicity. EO No. 5 (tea tree) exhibited the most potent anti- bacterial activity at multiple concentrations. Among the BOs, BO No. 2 (peppermint) maintained effective antibacterial activity, even at lower concentrations. Conclusions: Among the EOs tested, EO No. 9 (Hinoki-JP) showed the most potent antioxidant activity, whereas EO No. 5 (tea tree) exhibited the highest antibacterial activity. The cytotoxicity of individual oils can be modulated by blending; BO Nos. 2 (peppermint) and 4 (tea tree) maintained significant antibacterial activity, even at lower concentrations. These findings indicate that plant-derived EOs and their blends can be applied as natural functional materials in the food preservation, cosmetics, and pharmaceutical industries as alternatives to synthetic antioxidants and antimicrobial agents.