The Research On Extraction, Nanoemulsification And Antimicrobial Activity Of Essential Oil Of Eucalyptus Leaves

The essential oil of Eucalyptus leaves(EOEL), derived from oil gland cell, is a mixture including terpenes, aliphatic, aromatic compounds, etc. It exhibits various biological effects, such as antioxidant, antibacterial, insecticidal, and anti-inflammatory activities, and has been widely used in food, chemical, medicine industries, and so on. Now, research concerning EOEL at home and abroad was mainly focused on common fields, such as antibacterial, antioxidant activities. However, reports published about extraction technology optimization, differences between yield of EOEL and its antimicrobial activity, controlled releasing technology and the relationship between it and the corresponding antifungal activity, were rare. The optimum extraction technologies of EOEL were determined in this paper, taken eucalyptus robusta leaf as material, and taken antifungal activities & yield of EOEL as evaluation index. Differences of composition and contents of EOEL derivated from different extraction methods were found by GC-MS. Based on the establishment of emulsions with different size of EOEL, the relationship between the emulsion particle size of EOEL and its antibacterial activity was verified. And the feasibility to balance antimicrobial activity, storage stability and controlled releasing of EOEL had been confirmed preliminary. This study opened up a new space to broaden the utilization of Eucalyptus leaves, and might be provided experimental evidences for development of natural food preservative from EOEL.The results were as followings:1. First, the extraction technology of EOEL was optimized taken EOEL yield as indictor. The results showed that the extraction yield of EOEL reached up to 1.51% under following conditions, ie:solid to water ratio 1:4, ultrasound treatment 25 min, ultrasonic power 200 W, hydrodistillation time 5 h. Secondly, differences between EOEL yield and its antibacterial activity were explored taken the EOEL from each of orthogonal tests as material. The antibacterial activity of EOEL against Staphylococcus aureus and Escherichia coli was the strongest when the extraction conditions were as followings, ie: solid to water ratio 1:6, ultrasound treatment 30 min, ultrasonic power 180 W, and hydrodistillation time 5 h. As for Staphylococcus aureus and Escherichia coli, the inhibition zone diameter was (11.92±0.20) mm (n=3) and (10.25±0.35) mm (n=3), the minimum bactericidal concentration was 9 μL/mL and 6 μL/mL, respectively. But the corresponding extraction yield of EOEL of the two was only 1.28% coincidentally. As for Aspergillus niger, the strongest antimicrobial activity of EOEL obtained under conditions, ie:solid to water ratio 1:7, ultrasound treatment 30 min, ultrasonic power 200 W, hydrodistillation time 7 h. The inhibition zone diameter was (12.25±0.29) mm (n=3), and the minimum bactericidal concentration was 14 μL/mL, but the corresponding extraction yield of EOEL was 1.38%.2. The extraction technology of EOEL was optimized taken inhibition zone diameter against Penicillium and Aspergillus niger as index, respectively. The results showed that the antimicrobial activity of EOEL against Penicillium (EOELP) was the strongest when the extraction conditions were as followings, ie:solid to water ratio 1:6, ultrasound treatment 45 min, ultrasonic power 400 W, hydrodistillation time 8 h. Whereas, the antimicrobial activity of EOEL against Aspergillus niger (EOELA) was the strongest under conditions, ie:solid to water ratio 1:8, ultrasound treatment 45 min, ultrasonic power 470 W, hydrodistillation time 7 h. In order to explore the reason of differences concerning antimicrobial activity between EOELP and EOELA, GC-MS was used for detection and analysis. Significant difference was observed concerning of components and contents of EOELP and EOELA. Total of 68 kinds of compounds were identified in EOELP and EOELA, and 37 kinds of compounds existed in EOELP and EOELA simultaneously. The contents of oxygenated monoterpenes and sesquiterpene in EOELP were 78.52% and 43.03% more than that in EOELA, but the contents of monoterpenes and oxygenated sesquiterpene in EOELA were 15.63% and 123.69% more than that in EOELP. The a-pinenea was a major compound both in EOELP and EOELA, its contents in the former, was 3.78% more than that in the latter.3. In order to obtain an EOEL emulsion which not only had strong antimicrobial activity & good stability but also fulfilled controlled releasing, the stability of EOEL nanoemulsion, the relationship between particle size and the antimicrobial activity was researched, based on the establishment of emulsions with different size of EOEL. The results showed that the average particle diameter was (39.29±1.21) nm and polydispersity index (PDI) is 0.155±0.006 under following nanoemulsive technology, ie:compound of surfactant 12.77%(m/m), the ratio of cremophor EL 30 to ethanol 4:1 (m/m), EOEL 12.05%(m/m). The results obtained in stability test showed that the EOEL nanoemulsions had an excellent performance after 90 d. But inhibition zone diameter and minimum bactericidal concentration against Penicillium and Aspergillus niger showed non significant difference (P<0.05) between EOEL nanoemulsions with given grades of particle size and EOEL non-nanoemulsions. But unobvious regularity was exhibited among different grades of particle size namoemulsions concerning antimicrobial effects.