| Most edible plant essential oils exhibited excellent antimicrobial properties with high safety and low toxicity. However, its volatility, solubility and odor limited their applications in food system. To improve the volatility, aqueous solubility, and cover up the smell of plant essential oils become the primary challenge facing their industrial applications in food field as the natural preservative. Therefore, the antimicrobial properties of twelve edible plant essential oils to the food spoilage microorganisms was investigated. The synergistic effect between essential oils was then used to investigated by the checkerboard method. To improve the aqueous solubility and antimicrobial properties of the mixed essential oils by dilution carriers of solvent, emulsification and buried. The effect of dilution carriers on the antimicrobial activity of the mixed essential oils, evaluation of its quality and stability, the application in healthy drink of Chinese herbal medicine were researched in the study. It could provide a theoretical basis for the industrial applications of edible plant essential oils. Main contents and results were as follows:1、The antibacterial activity of twelve edible plant essential oils to the tested microorganisms (Bacillus subtilis ATCC 6633, Escherichia coli ATCC 25922, Staphylococcus aureus ATCC 25923, Aspergillus niger ATCC 16404, Aspergillus flavus ATCC 9643, Penicillium citrinum ATCC 9849, Saccharomyces cerevisiae GIM 2.207) were compared in the study, which including oregano oil, thyme oil, cinnamon oil, clove oil, cubeba oil, rosemary oil, anise oil, tea tree oil, eucalyptus oil, bergamot oil, clary sage oil, sage oil. Results showed that the tested microorganisms exhibit different susceptibility to twelve essential oils, especially Bacillus subtilis have most sensitive antimicrobial to essential oils. Based on an overall consideration of antimicrobial activity, oregano oil and thyme oil exhibited a broad spectrum of antibacterial activity with a concentration of 250μL/L. However, cinnamon oil has better antibacterial activity against fungi. The checkerboard method was then used to investigate the synergistic effect between essential oils. Combination of oregano oil and thyme oil showed an additive effect against all selected microorganisms.2、Gas chromatography-mass spectrometry (GC-MS) measurement was used to analyze the main chemical components of essential oils, which were phenolic and terpenic compounds. The main content of oregano oil, thyme oil and cinnamon oil were carvacrol, thymol and trans-cinnamaldehyde, respectively, which were the most antibacterial ingredients in plant essential oils.3、To improve the aqueous solubility and antimicrobial properties of the mixed essential oils with anhydrous ethanol,1,2-propylene glycol, glycerol as solvent agent, respectively. Result showed that anhydrous ethanol as solvent agent can effectively improve the aqueous solubility of essential oils. Based on the overall antimicrobial effect, while 1,2-propylene glycol as solvent in a certain extent can improve their antibacterial activity.4、The stable oil-in-water microemulsions could be fabricated using Tween-80 as a surfactant, anhydrous ethanol as a cosurfactant and oregano-thyme compound as an oil phase via construction of pseudo-ternary phase diagrams, which was a light yellow and transparent liquid. When the Km value was equal to 3:1, the system has the largest area of microemulsion region (29.55%) and the minimum dilution ratio (9:1). The corresponding surfactant-to-oil ratio was 6.76:1. Selected formulations (F1-F3) were characterized for droplet size distribution, polydispersity index (PDI), viscosity, zeta potential. Based on lowest droplet size (13.0±0.6nm), lowest PDI (0.231±0.020), optimal zeta potential (-22.23±0.24mV), microemulsion F3 was found to have better resistance to salt, glucose, acid and alkali, as well as good storage stability. However, compared with anhydrous ethanol as solvent agent, the antibacterial effect of microemulsion F2 were found to be greatly weaken against the tested microorganisms.5、The microcapsules containing oregano oil and thyme oil (1:1) were prepared using β-cyclodextrin as wall-forming material, were white and loose powder. Scanning electron microscopy (SEM) observed that the majority of microcapsules were smooth and dense box shaped crystal with differences in particle size and multiple cracks. It has the unique smell of oregano-thyme compound, soft but not pungent. The recovery rate was 79.8%, the embedding rate as high as 86%. Gas chromatography-mass spectrometry (GC-MS) measurement was used to analyze the chemical components of unencapsulated and encapsulated oils, demonstrating that the process of microencapsulation did not deteriorate the encapsulated essential oils. However, it showed poor solubility with the maximum solubility was only 2.5g/L in the boiling water. The retention rate of essential oils in microcapsules still amounted to 83% under 28℃ and 80℃ storage conditions, indicating that the poor release characteristics. Compared with anhydrous ethanol as solvent agent, the antibacterial activity of microcapsules was also greatly weaken against the tested microorganisms.6、The application of essential oils in healthy drink of Chinese herbal medicine was researched in the study. When anhydrous ethanol as solvent agent,0.05% w/w oregano-thyme compound exhibited excellent bactericidal effect under the room temperature (30℃), which total numbers of colony to keep floating in the range of 103CFU/mL within 5 days and number of mold to meet the food industry standard after a day. When 1,2-propylene glycol as solvent agent,0.025% w/w oregano-thyme compound showed better bacteriostatic effect at 4℃, which total numbers of colony and mold basically reached the standard of food industry within 60 days. Therefore, sensory evaluation and physical and chemical properties were researched. The effect of essential oils on the odor and taste of the concentrate were found to be significant difference. The flavour of concentrate treated with 0.025% w/w oregano-thyme compound was found to be acceptable, in which the influence on the content of amino nitrogen and reducing sugar for concentrate were little. |
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