Study on Contribution of Microwave to Changes of Chemical Composition in Extraction of Essential Oils
Essential oil from mentha hapioealyx briq and zanthoxylum bungeanum maxim was extracted by solvent free microwave extraction(SFME) and microwave assisted hydro-distillation(MAHD),and GC/MS was used for the qualitation and quantification analysis for the chemical composition in the essential oils.Hydrodistillation(HD) was compared to study the contribution of microwave to the composition changes in the extraction process.The experimental results showed that microwave can promote the menthol from the essential oil of mentha hapioealyx briq oxidized into pulegone and slight mint furanone.The eucalyptol from the essential oil of zanthoxylum bungeanum maxim would be transformed to α-linalool through arrangement reaction catalysis by proton in high temperature environment for a long time.When the microwave action time was exceeded 50-70 min,above arrangement reaction would be promoted.When action time of microwave was less than 50 min,above arrangement reaction almost did not be observed.Microwave can speed up the extraction,especially for SFME.By microwave method,the extraction time is so short(40 min) that above rearrangement was avoided and more eucalyptol was obtained.In comparison with microwave method,more rearrangement product of α-linalool was obtained by HD method,and MAHD is the medium of above two methods.