Antimicrobial Activity And Microcapsulation Properties Of Eucalyptus Essential Oil

Eucalyptus essential oil has the advantages of abundant resources,low price,high safety,and broad spectrum antibacterial properties.Nevertheless,EEO is poor in stability,easily oxidized and volatilized.Therefore,it is difficult for storage and preservation,thus limiting its application in food,medicine and other fields.Microcapsule technology can solve the above problems,but the EEO can only evaporate into the space in the form of gaseous molecules after microencapsulated.The issues of the influence of temperature and oxygen on the composition and antibacterial activity of EEO,and how the EEO release after encapsulated are not yet conclusive.For that reason,this article has studied the antibacterial activity and composition of EEO gas,and the influence of temperature and oxygen on the composition and antibacterial activity of EEO.EEO microcapsules were prepared using ?-cyclodextrin(?-CD)as the wall material.The optimal inclusion technologies of microcapsules were determined,and then characterized the structure.Finally,a series of controlled release experiments was conducted to analyze the release characteristics of EEO microcapsules.This study will provide basis for the preservation of the EEO in the modified atmosphere.The main research contents and results are as follows:(1)The study based on antimicrobial potential and compounds of vapor-phase EEO.Antimicrobial activity of EEO vapor against Escherichia Coli and Staphylococcus Aurous were stronger than Aspergillus Niger.The vapor phase MIC value(0.045~0.36 mg/m L)to the tested microorganisms was significantly lower than liquid-phase MIC(4.5~18 mg/m L)and solid phase MIC(4.5~18 mg/m L).SPME/GC-MS test results showed that the dominant components of EEO and EEO vapor were terpenes and alcohols.The antibacterial activity of EEO vapor was related to ?-pinene,D-Limonene,3-Carene,Terpinolene and Myrcene.(2)Effects of temperature and oxygen on antimicrobial performance and composition of EEO.Studies have shown that the main components of EEO after treatment in three different ways(high-temperature and air,high-temperature and nitrogen,room temperature and air)were the same as EEO,and were dominanted by terpenes and alcohols.Antimicrobial performance of EEO was not significantly differ by temperature and oxygen,and MIC of EEO after treatment was similar to that of EEO.High-temperature and airtreated EEO(mixed oil)appeared clearly stratified.The main components of the upper oil and mixed oil were mainly terpenes and alcohols,while the lower oils were mainly alcohols and ketones.The antimicrobial results showed that the MIC value of the upper oil was slightly lower than that of the original EEO,while the lower oil was greater than that of the original EEO.(3)Process optimization of microencapsulation and structure characterization on the EEO.The most appropriate conditions were: inclusion temperature 40?,inclusion time 1.5 h,wall-core ratio 8:1,under which,the inclusion efficiency was 70.33% and microcapsule yield was 86.27%.Scanning electron micrographs(SEM)revealed the the structure of EEO microcapsules has transformed,resulting in smooth surface of the crystal structure.The size distribution obtained by laser light scatting indicated that the diameters of the majority of microcapsules were ranging from in 4.0 to 30 ?m.Fourier transform infrared spectroscopy(FTIR)revealed the formation of microcapsules.Differential scanning calorimeter(DSC)and thermogravimetric analysis(TGA)results indicated that encapsulation enhanced the stability and prolonged the acting time of EEO.(4)Studies conducted on the controlled release of EEO microcapsules.Release kinetics of EEO from the microcapsules was investigated by zero-order kinetics,first-order kinetics and Avrami's equation.The result showed that the release model of EEO from microcapsules fitted better for Avrami's equation.Kinetics analysis based on the Avrami's equation revealed that the release of EEO was accelerated with the increases of RH and temperature.For storage time treatment,the volatilization of EEO was significantly inhibited after encapsulation.For all treatments,the release parameter n was between 0.5 and 1.0,which presenting a diffusion-limited and first-order mode.High temperature stability test further revealed that EEO was protected after having been encapsulated into ?-CD.The release of EEO microcapsules can be achieved by changing the temperature,humidity and time,which provides theoretical basis for its storage and uses.