Composition Analysis of Essential Oil from Melaleuca bracteata Leaves Using Ultrasound-assisted Extraction and its Antioxidative and Antimicrobial Activities

To extract essential oil from Melaleuca bracteata leaves without thermal degradation, ultrasound-assisted extraction (UAE) was developed and optimized using a response surface method (RSM) based on the Box-Behnken design (BBD). Under the optimized extraction conditions, a higher essential oil yield of 4.55% was achieved in comparison to that of 1.02% via the conventional hydrodistillation extraction method, which suggested that UAE could be used as an alternative and efficient extraction method for the essential oil from M. bracteata leaves. Furthermore, the composition of the essential oil extract was analyzed by gas chromatography-mass spectrometry. The results showed that 42 constituents, including methyl eugenol (86.5%), methyl cinnamate (4.33%), 3,4,5-trimethoxybenzoic acid, methyl ester (1.77%), and germacrene D (1.24%) were identified in the essential oil of M. bracteata leaves. The essential oil showed strong 2,2-diphenyl-1-picrylhydrazyl (DPPH), 2,2'-azino-bis(3-ethylbenzthiazoline-6-sulphonic acid) (ABTS) radical scavenging activity, and reducing property. Additionally, remarkable bacteriostatic activity was observed against the tested pathogens, including Chromobacterium violaceum ATCC31532, Pseudomonas aeruginosa PAO1, Serratia marcescens MG1, and Serratia marcescens H30. These results indicated that the essential oil from M. bracteata leaves had potential applications due to its antioxidative and antimicrobial activities.