Variation in the Antibacterial and Antioxidant Activities of Essential Oils of Five New Eucalyptus urophylla ST Blake Clones in Thailand

Eucalyptus oils are widely used for a variety of purposes. This study investigates the terpenoid compositions and antibacterial and antioxidant activities of eucalypt leaf oils extracted from four E. urophylla clones and one E. urophylla x E. camaldulensis hybrid clone grown in Thailand. According to GC/MS analysis, the E. urophylla oils were mainly composed of 1,8-cineole, alpha-terpinyl acetate, beta-caryophyllene, and spathulenol, while 1,8-cineole, alpha-terpinyl acetate, p-cymene, and gamma-terpinene were mostly identified in the hybrid oil. All eucalypt oils exhibited a significant bacteriostatic effect against Gram-positive bacteria, Streptococcus pyogenes, Staphylococcus aureus, Listeria monocytogenes, and Bacillus cereus. Only the hybrid oil had an effect on all Gram-negative bacteria tested, including Salmonella typhi, Escherichia coli, Pseudomonas aeruginosa, and Enterobacter aerogenes. These oils have antibacterial properties that vary according to their terpenoid content. Only the hybrid oil had a potent antioxidant effect, with an IC50 value of 4.21 +/- 0.35 mg/mL for free radical (DPPH) scavenging. This oil's antioxidant effect may be a result of the phenolic terpenoids, thymol and carvacrol. As a result, these oils may be a novel source of antibacterial and antioxidant agents. Additionally, the antibacterial and antioxidant capabilities of the E. urophylla x E. camaldulensis hybrid essential oil are reported for the first time.

Automated summary

This study investigates the terpenoid compositions and antibacterial and antioxidant activities of eucalypt leaf oils from different clones grown in Thailand. The results show that these oils contain various compounds and exhibit significant antibacterial and antioxidant effects. The hybrid oil demonstrates a broader antibacterial activity and a potent antioxidant capability.