Melaleuca alternifolia: Analysis by GC-MS and Antimicrobial activity

Melaleuca alternifolia (Maiden & Betche) Cheel (Myrtaceae) is an Australian medicinal plant, known as 'tea tree’. The 'tea tree’ essential oil (TTO) contains some volatile components such as terpinen-4-ol, α-terpineol and 1,8-cineole. This oil shows a broad-spectrum activity such as antibacterial, antifungal, antiviral, antitumor and antiprotozoal activities. Terpinen-4-ol and α-terpineol have actually been claimed to be the two of the main components in TTO antimicrobial activity (Kong et al., 2019; Zhong et al., 2012). According to the literature there are six Melaleuca chemotypes each one with a distinct chemical composition. They are divided into terpinen-4-ol chemotype, a terpinolene chemotype, and four 1,8-cineole chemotypes (Homer et al., 2000). Despite these chemical variabilities of the oils, there are numerous companies marketing of TTO, and no obvious differences was observed in their bioactivity. In this work, two commercial TTO samples were analyzed by GC-MS. The mass spectrometry analysis showed the presence of p-cineole (8.3%), α-terpineol (9.3%), 4-nonanone (9.1%), terpinen-4-ol (12.4%) as major constituents for sample 1. In the sample 2 was identified (+)-4-carene (11.2 %), γ-terpinene (13.6%) and terpinen-4-ol (17.5%) as major constituents. Antifungal activity was observed in agar diffusion assay using commercial oils after 48 h. All Candida spp. and Aspergillus species tested were susceptible to both samples with inhibition halo between 1 and 2.7 cm. According to the literature, the antimicrobial activity of TTO is associated with terpinen-4-ol and α-terpineol content. Sole on the sample 1 was observed the concomitant presence of terpinen-4-ol and α-terpineol, however the terpinen-4-ol content is higher in the sample 2. Despite the difference in chemical composition, both samples showed antimicrobial activity against Candida spp. and Aspergillus spp. strains tested. Thus, the biological activity observed can be correlated with the presence of terpinen-4-ol content. The antimicrobial activity of TTO samples against these microorganisms indicate the potential for their possible incorporation into textile fibers for therapeutic purposes.

References

Homer, L. E., D. N. Leach, D. Lea, L. S. Lee, R. J. Henry, and P. R. Baverstock. 2000. Natural variation in the essential oil content of Melaleuca alternifolia Cheel (Myrtaceae). Biochem. Syst. Ecol. 28:367–382

Zhong, Z.; Yuan, Y.; Fan, L. 2012. Antibacterial composition diversity of introduced Melaleuca alternifolia oil. Zhongshan Daxue Xuebao, Ziran Kexueban 51: 7-13.

Kong, Q.; Zhang, L.; An, P.; Qi, J.; Yu, X.; Lu, J.; Ren, X. 2019. Antifungal mechanisms of α- terpineol and terpene-4-alcohol as the critical components of Melaleuca alternifolia oil in the inhibition of rot disease caused by Aspergillus ochraceus in postharvest grapes. J. Appl Microbiol, 126:1161-1174.