Evaluating the multifaceted bioactivity of Syzygium aromaticum essential oil: the central role of eugenol.

Abstract

Background/aim: Syzygium aromaticum L. is a versatile plant traditionally used to treat digestive and respiratory issues, improve oral health, and relieve pain, particularly in regions such as Southeast Asia, South Asia, and parts of the Middle East. Its essential oil (EO), predominantly composed of eugenol, is rich in bioactive compounds. This study aims to clarify the specific contribution of eugenol to the antioxidant, antibacterial, antifungal, and insecticidal activities of S. aromaticum EO by comparing their individual effects. Additionally, density functional theory (DFT) calculations were employed to examine the antioxidant mechanism of eugenol and its role in enhancing the overall activity of the EO.

Materials and methods: The EO was obtained from S. aromaticum and analyzed using GC-MS to determine its composition. Antioxidant activity was assessed through the DPPH scavenging assay. Antibacterial and antifungal activities were evaluated using the disk diffusion method against various strains, while insecticidal and repellent effects were tested on Bruchus lentis at different concentrations and exposure times. Antioxidant mechanisms were investigated using DFT calculations.

Results: The findings underscore the strong antioxidant, antibacterial, antifungal, and insecticidal properties of S. aromaticum EO, with eugenol identified as the primary active component driving the antioxidant and insecticidal effects. Additionally, eugenol has been found to exhibit moderate scavenging activity in lipid media. However, its activity is higher in polar media, with a k _overall = 1.70 ⊠ 10⁶ M^-1s^-1 comparable to that of ascorbic acid. The single-electron transfer mechanism from the deprotonated state was found to play a decisive role under these conditions.

Conclusion: S. aromaticum EO exhibits remarkable antioxidant, antibacterial, antifungal, and insecticidal activities. A significant portion of these properties can be attributed to the presence of eugenol. This suggests that eugenol plays a critical role in the EO's overall efficacy, making S. aromaticum a promising candidate for applications in natural health products, pharmaceuticals, and agricultural pest management.