| Since the 21st century,the abuse of antibiotics in agriculture,forestry and animal husbandry has led to the emergence of super(drug-resistant)bacteria more and more frequently,which leads to the waste of medical and social resources.In order to solve this urgent practical problem,developing antibiotic substitutes is an effective solution.As a secondary metabolite of plant origin,plant essential oil has excellent biological activities such as inect repellent,sterilization and anti-virus.And these biological activities are produced by the synergistic effect of dozens of organic compound components,which can effectively reduce the drug resistance of harmful microorganisms.Developing them as antibiotic substitutes has broad and good research prospects.In this paper,the essential oil extracted from Melaleuca alternifolia Cheel from Australia and China was mixed with Litsea cubeba and Origanum essential oil.The antibacterial activity,chemical composition,antibacterial stability and antibacterial mechanism of Melaleuca alternifolia Cheel and its compound essential oil against three common foodborne pathogens were studied.The research results are as follows:(1)Taking gram-negative Escherichia coli,gram-positive Staphylococcus aureus and fungal Saccharomyces cerevisiae as the tested strains,through the drug(essential oil)patch test method,it is concluded that the essential oils of Melaleuca alternifolia Cheel,Litsea cubeba and Origanum can express antibacterial activity against the three tested strains,but there are significant differences in the inhibition intensity of a single essential oil against different strains.Through the comprehensive analysis of bacteriostatic performance and Mic/MBC value under the diameter of bacteriostatic circle and concentration gradient,Litsea cubeba essential oil with strong bacteriostatic activity was selected to be compounded with Melaleuca alternifolia Cheel essential oil,and Escherichia coli with the highest bacteriostatic difficulty was used as the tested bacteria to test the bacteriostatic activity of the compounded essential oil under different formulas.It was determined that the antibacterial activity of Litsea cubeba essential oil was the best at the volume ratio of 6:4.When the concentration of essential oil was 18.00mg/ml,the antibacterial range against Escherichia coli reached 18.36 ± 0.41,which was increased by 9.74%compared with the single prescription of Litsea cubeba essential oil;The MIC of the three tested bacteria was 1.12-2.25mg/mL,which was 0-4 times higher than that of the essential oil of Melaleuca alternifolia Cheel.(2)The components of essential oil were analyzed by GC-MS and NMR.The results showed that the essential oil of Melaleuca alternifolia Cheel was composed of 20 chemical components,of which the main component was 1,8-cineole(35%-38%),α-Terpineol(21.0%-24.0%)and α-Terpenes(9.0%-12.0%)account for 65-74%of the components of essential oil,belonging to "Eucalyptus" tea tree oil;The compound Melaleuca alternifolia Cheel oil(6:4)consists of 26 chemical components,of which the main components are 1,8-cineole(34%-34.5%),citral(16.5%-17.0%),4-terpineol(14.2%-14.5%)and citronellal(11.2%-11.9%),accounting for 75.9%-77.9%.After compounding,the number of alcohols and hydrocarbon compounds increased,the relative content decreased,and a total of 3 aldehydes and ketones were added;The original ether compound 1-bromo-2,3,3-trifluoro-l-cyclopropene disappeared.After compounding the main chemical components of Melaleuca alternifolia Cheel essential oil,the decline range of its relative content is not the same as that calculated by volume ratio,and there may be reaction consumption between multiple compounds.The combined test of the main characteristic components in the compound essential oil shows that there are various interaction mechanisms between the characteristic components of the essential oil,and the final antibacterial results against Escherichia coli show that the compound enhances the antibacterial properties of the essential oil:4-terpineol Combined use with citral played a synergistic effect;4-terpineol combined with 1,8-cineole played an additive effect;1,8-cineole showed no correlation with citral.(3)The antibacterial activity of essential oil in different UV irradiation environment and its effect on white leaf were tested.It was found that the environmental pH had a significant effect on the antibacterial activity of essential oil.The antibacterial activity increased under the acidic condition of pH≤6 and decreased under the alkaline condition of pH≥7.High temperature heating and UV irradiation had no significant effect on the stability of antibacterial activity of essential oil.(4)Melaleuca alternifolia Cheel and its compound essential oil had significant effects on the growth curve,cell dissolution,extracellular potassium ion concentration and nutrient utilization of the three tested bacteria.Through the analysis of the results,the bacteriostatic mechanism is to inhibit the growth and reproduction of bacteria by inhibiting the activity of bacterial life activities and reducing the utilization of external carbon sources,nitrogen sources and other nutrients;On the other hand,it leads to bacterial death by affecting the stability and integrity of bacterial cell wall membrane system. |
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