## 4 Discussion
Furthermore, the free radical scavenging effect was measured with DPPH. The characteristic indigo color disappears when a relatively stable radical converts to a nonradical with electrons or hydrogen donated from an antioxidant. Using this characteristic, DPPH is widely used to measure the antioxidant activity of natural products due to its high correlation with actual antioxidant activity [43]. Therefore, 83.59% DPPH radical scavenging activity was observed at 1 mg/mL COE concentration, showing similar activity to a control group, gallic acid (89%). This confirms the high antioxidant power of COE with its high DPPH radical scavenging function. When compared to the essential oils from _Pinus densiflora_, _Pinus koriaensis_, and _Chameocarpis pisifera_, COE oil has one of the best antifungal properties. Specifically, it has been reported that yoshixol, isolated and purified from _C. obtusa_ wood, has strong antifungal effects against _Escherichia coli_, _Mycobacterium chelonae_, _Pseudomonas aeruginosa_, and _C. albicans_[44]. Furthermore, COE oil inhibits mycelial growth of the two dermatophytes (_Microsporum canis_ and _Trichophyton metagroroflytes_) at a concentration of 500 ppm and shows antifungal properties [36]. This study also confirmed the antifungal effects of COE on oral candidiasis. The higher the concentration of COE, the greater the diameter of the zone of inhibition, showing its devastating effect on _C. albicans_. However, no significant difference was observed between the concentrations ranging from 2.5 mg/mL to 30 mg/mL (\(p>0.05\)). COE showed complete antifungal properties at a 30 mg/mL concentration. This result is consistent with the result of [PERSON] et al. [19], which reported increased strain growth inhibition with increased COE concentration. Furthermore, [PERSON] et al. [20] indicated the continuous growth inhibition of _C. albicans_ when cultured with 0.25% _phytoncide_, decreasing the number of viable cells and resulting in the total elimination of _C. albicans_ in 20 h. The growth-suppressing and lethal effects of _plytoncide_ on _C. albicans_ are consistent with the findings of this study. It has been reported that the antimicrobial mechanism of essential oils is due to _plytoncide_ damaging the cell membranes of microorganisms and increasing their permeability to induce cytoplasmic liberation or affecting the bacterial respiratory metabolism [23; 45]. Even though _plytoncide_ shows antifungal effects against _C. albicans_ and can kill cells through cell lysis, the level of cytotoxicity and cell viability depend on the concentration. After observing _C. albicans_ with an electron microscope for 6 h after the _plytoncide_ treatment, [PERSON] et al. reported an increased number of atypical cell shapes, an increased electron density of the cytoplasm, increased high-density granules, and the division of intracellular organelles becoming more unclear in higher concentrations. Therefore, this study used HaCaT cells to confirm the safety of COE, which revealed a lower survival rate of HaCaT cells at higher concentrations, thus confirming its cytotoxicity. Overall, the COE concentration of 2.5 mg/mL indicated a clear antimicrobial effect without any observable cytotoxicity. Additional clinical studies are needed to actively utilize COE as a safe natural antibiotic. Therefore, it is necessary to confirm substantial changes in the patient's oral condition by applying COE-containing gargles to humans in the clinical field. In addition to these functional confirmations, additional research will be needed to confirm the applicability of COE-containing gargles by examining satisfaction with the use of gargles. For further research, through research on the quantification of phytochemical compounds of COE that cause antifungal effects, it is necessary to carry out chemical evaluation through component analysis. Above all, research should be conducted to confirm the continued harmlessness to the human body by analyzing the safety test through more specific and diverse experiments.