Chemical Composition,Antibacterial And Antioxidant Activities Of Essential Oils From Two Types Of Citrus And Litsea Cubeba

Citrus and Litsea cubeba are widely distributed and in high demand in the market.The essential oils of citrus and L.cubeba have biological activities such as antibacterial,antioxidant,anticancer and insecticide,which can be used in food,medical and daily chemical industries.In this study,the cold-pressed essential oils of two citrus species（sweet orange and lemon）were subjected to molecular distillation,and the oils were stored at 4°C for five years before being examined for their chemical composition,antibacterial and antioxidant activities.The L.cubeba essential oil was extracted by hydrodistillation and processed by reduced-pressure distillation,and the chemical composition,antibacterial and antioxidant activities of the essential oil and the distillation fractions were investigated.Further,the highly active distillation fractions of sweet orange and the L.cubeba essential oil were compounded and tested for their antibacterial effects.The main findings were as follows.1.Identification of the chemical composition of sweet orange and lemon essential oils.The essential oil components were identified by gas chromatography-mass spectrometry（GC-MS）analysis.26,17,23,and 27 compounds were identified for the cold-pressed sweet orange essential oil,the light-phase fraction of sweet orange essential oil,the cold-pressed lemon essential oil,and the light-phase fraction of lemon essential oil,respectively.A total of 50 compounds were identified for the four essential oils.In comparison to the essential oils before preservation,the essential oils preserved for 5 years had a significant amount of terpene oxides.2.Study on the antibacterial and antioxidant activities of sweet orange and lemon essential oils.The antibacterial activity of sweet orange and lemon essential oils and the four monomeric components were determined by the inhibition circle method and micro broth dilution method,and the results showed that the light phase fraction of sweet orange essential oil showed good antibacterial activity against Bacillus subtilis,Staphylococcus aureus,Escherichia coli and Salmonella,with minimum inhibitory concentrations（MIC）of 0.39,0.78,0.39 and 0.39μL/m L,respectively;while the cold-pressed sweet orange essential oil and lemon essential oil showed weaker inhibitory activity.In addition,all four monomers in the sweet orange light phase had weaker antibacterial activity than the sweet orange light phase,indicating the existence of other antibacterial active substances or a synergistic effect among active substances.The antibacterial activity of the light phase of sweet orange essential oil preserved for 5 years was stronger than that before preservation,probably due to the effect of newly produced terpene oxides.The antioxidant activity of the four essential oils was evaluated using the DPPH and ABTS methods,and the results showed that the sweet orange essential oil light phase fraction had the best antioxidant activity with IC₅₀ of 22.62 mg/m L（DPPH）and 4.26 mg/m L（ABTS）,respectively.3.Study on the differences in the composition and content of essential oils between healthy and Huanglongbing infected leaves of navel oranges.The essential oils of four leaves（healthy new leaves and healthy old leaves,new leaves and old leaves infected with Huanglongbing）of Gannan"Newhall"navel orange were extracted by supercritical CO₂ extraction technique,and the components of the four essential oils were analyzed and identified by GC-MS.The main components included sabinene,3-carene,limonene,cis-β-ocimene,and linalool.There were differences in the content of each component between the essential oils of new and old leaves,and the composition and content of essential oil compounds changed in leaves infected with Huanglongbing compared with healthy leaves.4.The chemical composition,antibacterial and antioxidant activities of L.cubeba essential oil and three reduced-pressure distillation fractions were analyzed.The essential oil components were identified by gas chromatography-mass spectrometry（GC-MS）.44,26,29 and 21 compounds were identified in the essential oil,fraction 1,fraction 2 and fraction 3,respectively,for a total of 44compounds.The antibacterial activity of the four essential oils was determined by the inhibition circle method and the micro broth dilution method.Fraction 3 had the strongest antibacterial activity with MIC values of 0.39 and 0.78μL/m L for B.subtilis and S.aureus,respectively.The IC₅₀ values were 2.23 mg/m L and 2.57 mg/m L,respectively.Fraction 3 was compounded with sweet orange light phase and tested for antibacterial effect,and it was found that a certain ratio of the compounded essential oils showed a synergistic effect on S.aureus.In conclusion,the light phase fraction of sweet orange showed strong antibacterial activity after five years of preservation,which can provide a reference for the development of new natural antibacterial agents;the comparative study of four essential oil components of Gannan"Newhall"navel orange can provide a theoretical basis for the development of new insecticides;the distillation fraction of L.cubeba essential oil with strong antioxidant activity and antibacterial activity can be used as a natural antioxidant and a natural alternative to chemical bactericides.