| Grapefruit,sweet orange oil,bergamot,lemon oil and D-limonene were selected in this experiment.The antibacterial and antioxidant activities of citrus essential oils and their protective effects on mice infected with E.coli were studied in vitro and in vivo.Experiment 1:Analysis of active components in citrus essential oils.The objective of this study was to determine the main active components of essential oils from grapefruit,sweet orange oil,bergamot,lemon oil and D-limonene by GC-MS.The results showed that the main active components of grapefruit,sweet orange oil,bergamot,lemon oil and D-limonene were terpenes,among which D-limonene was the highest,accounting for 81.56%,78.30%,34.23%,47.48%and 83.52%of the essential oils,respectively,.Experiment 2:Antibacterial activity of citrus essential oilThis study was to determine minimum inhibitory concentration(MIC),minimum bactericidal concentration(MBC)and inhibition zone diameter(IZD)of five citrus essential oils to compare their antibacterial activities.Among the five kinds of essential oils,grapefruit essential oil had the lowest MIC to E.coli,and lemon oil had the lowest MBC to E.coli.The MIC value of grapefruit essential oil was 2.5mg/ml,and the MBC value of lemon oil was 10 mg/ml.The MIC value of D-limonene to Salmonella was the lowest,which was 1.25 mg/ml;the MBC value of lemon oil and D-limonene was the lowest,which were both 40 mg/ml.The MIC of D-limonene to Lactobacillus was 40 mg/ml,the MBC of D-limonene to Lactobacillus was 80 mg/ml.The results of disk diffusion assay showed that when the concentration of essential oil was 80 mg/ml,the inhibition rates of five plant essential oils on E.coli were lemon oil>bergamot>D-limonene>sweet orange oil>grapefruit;the inhibition rates on Salmonella were grapefruit>lemon oil>bergamot>sweet orange oil>D-limonene;the inhibition rates on lactobacillus were grapefruit>D-limonene>sweet orange oil>bergamot>lemon oil.Experiment 3:Antioxidant activity of citrus essential oilsIn this study,the antioxidant activities of the five citrus essential oils were compared by DPPH free radical scavenging assay,ABTS free radical scavenging assay and Inhibition assay of yolk peroxidation.There were significant differences in DPPH free radical scavenging rate,ABTS free radical scavenging rate and yolk lipid peroxidation inhibition rate between citrus essential oils and their different concentrations(P_E<0.01,P_C<0.01),and there were significant differences in their interaction(P_E*P_C<0.01).Among them,lemon oil and bergamot have better scavenging effect on DPPH free radical;D-limonene and lemon oil had better scavenging effect on ABTS free radical;D-limonene and bergamot have better inhibition on yolk lipid peroxidation.The different antioxidant activities of plant essential oils may be the result of the interaction of various active components.Experiment 4:Effect of essential oils on mice infected with E.coliThis experiment was conducted to study the effect of lemon oil and D-limonene on mice infected with E.coli.5-week male Balb/c mice weighing 18～20 g were divided into 8 groups,total 64:NS group(normal saline group),E.coli group(E.coli group),lemon oil group(300,600,1200 mg/kg)and D-limonene group(300,600,1200 mg/kg).Mice in NS group and E.coli group were given normal saline by gavage,and mice in essential oil group were given two different concentrations of essential oil by gavage for one week.One hour after the end of gavage on the seventh day,mice in the NS group were intraperitoneally injected with normal saline,and mice in the other groups were intraperitoneally injected with E.coli.Plasma was collected for determination of antioxidant indexes and inflammatory factors.The anterior part of duodenum was used for HE staining,and the posterior part of duodenum was used to determine the relative expression of tight junction protein m RNA.There were significant differences between E.coli group and NS group(p<0.01).1)Among the plasma antioxidant indexes,lemon oil group(low concentration)and D-limonene group(medium concentration)were significantly different from E.coli group(p<0.01),which could effectively reduce the content of MDA;Lemon oil group(low concentration)and D-limonene group(medium concentration)were significantly different from E.coli group(p<0.01),which could effectively reduce the content of MPO;The difference between lemon oil group(low concentration)and E.coli group was extremely significant(p<0.01),which could effectively increase the content of SOD,while the difference between D-limonene group(medium concentration)and E.coli group was significant(p<0.05).2)Among plasma inflammatory factors,there were significant differences between E.coli group and lemon oil group(low concentration)and d-limonene group(medium concentration)(p<0.01),which could significantly reduce TNF-α,IL-1βand IL-6 in mice.3)Compared with NS group,E.coli group showed typical pathological changes,including increased nuclear aggregation,increased inflammatory cells,glandular disorder,sparse villi and so on.The pathological changes of lemon oil group and D-limonene group were improved,and with the increase of concentration,the damage degree was smaller.4)Among the tight junction protein indexes,lemon oil group(medium concentration)and d-limonene group(low concentration)were significantly different from E.coli group(p<0.01),which could significantly increase the relative m RNA expression of ZO-1,occludin and claudin in mice.In conclusion,lemon oil and D-limonene in medium concentration can alleviate and improve the intestinal barrier damage caused by E.coli infection in mice,and the effect of lemon oil is better.Conclusion:The main active components of essential oils from grapefruit,sweet orange,bergamot,lemon and D-limonene were terpenes.The results showed that all the five citrus essential oils had selective antibacterial activity,and showed strong antioxidant activity in the way of significant interaction between the type of essential oil and its concentration.Among them,lemon oil can better alleviate the intestinal injury in mice infected by E.coli... |
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