Study On The Bioactivities And Active Constituents Of Eucalyptus Globulus Leaves

The aim of this study was to study bioactivities of volatile components and aqueous extracts of Eucalyptus globulus leaves,and analysis of the bioactive constituents in those extracts,and to apply microwave hydrodiffusion and gravity method(MHG)to green,non-destructive extraction for volatiles of Eucalyptus globulus leaves.The main contents were as follows:Firstly,allelopathy of volatile components and antibacterial,antioxidation and allelopathic activities of the aqueous extracts of Eucalyptus globulus leaves were studied.It was found that the volatile components of Eucalyptus globulus leaves had a significant inhibitory effect on the germination and germination of the seeds,and the inhibitory effect was positively correlated with the amount of Eucalyptus globulus leaves.The results showed that the aqueous extract of Eucalyptus globulus had significant inhibitory effect on Escherichia coli and Bacillus subtilis,but no significant inhibitory effect on Pseudomonas aeruginosa.The aqueous extract of Eucalyptus leaves had high antioxidant activity in the range of 20-200 ?/mL,and the IC50 value was 56 ?g/mL.Also it was found that aqueous extract of Eucalyptus globulus leaf had significant inhibitory effect on grass seeds,and the inhibitory effect was positively correlated with the concentration of the extract.Secondly,qualitative and quantitative analysis of volatile components from Eucalyptus globulus leaves using HS-SPME-GC-MS and internal standard method was established.The optimum extraction conditions were as follows:equilibrium time was 30 min,extraction time was 40min and extraction temperature was 50?.A total of 127 volatiles were identified from the leaves of Eucalyptus globulus.11 major monoterpene compounds and 8 sesquiterpenoids were quantified by internal standard.Eucalyptol was highest contents in the leaves,and its concretration in fresh eucalyptus leaves and dried eucalyptus globulus was 127.19 ?g/g and 86.61 ?g/g respectively.It was hypothesized that eucalyptol and ?-pinene might be the main bioactive constituents of the volatiles of Eucalyptus globulus leaves.Then,volatiles of Eucalyptus globulus leaves were extracted by microwave hydrodiffusion and gravity method(MHG),and the extraction conditions were optimizedas as follow:extraction temperature was maintained at 70 ?(±1?)and extraction time was 20 min.A total of 127 volatile compounds were identified,and the two main volatile components were eucalyptol and ?-pinene,the contents of which were 22.67%and 13.20%,respectively.Microwave hydrodiffusion and gravity is a green,undamaged method for volatiles extracted compared with headspace solid-phase microextraction(HS-SPME)and hydrodistillation extraction(HDE).MHG would be a good alternative to traditional HDE for its green extraction without addition of solvent or water but with low temperature,and to HS-SPME for its numerous extractions with low cost and energy for the isolation of volatiles from Eucalyptus globulus leaf.Finally,the total phenol content in the aqueous extract of Eucalyptus globulus was determined to be 0.72 mg/mL and the total flavonoid content was 0.17 mg/mL by spectrophotometry.The bioactive components of the aqueous extracts were analyzed by UPLC-Q-orbitrap-MS,and 34 components were identified with 14 polyphenols,9 glycosides,4 tannins.Gallic acid was the highest content in the water extract of Eucalyptus globulus,which was accounting for 2.81%.It might be an important compound and related to the bioactivity of the aqueous extract.So,the content of gallic acid in the aqueous extract of Eucalyptus globulus was determined by liquid chromatography and its average content was 0.52 mg/mL by the standard curve of gallic acid.