| Summary: | 碩士 === 國立嘉義大學 === 食品科學系碩士班 === 93 === Essential oils such as spearmint, rosemary, lavender and lemongrass have a great effect upon antibacterial activities. Since they are hydrophobic, have low solubility in foods and solution. Four commercial essential oils (spearmint, rosemary, lavender and lemongrass) were analyzed by GC-MS. Four essential oils were emulsified by different treatments and emulsifiers. The emulsifiers are characterized into 8, 11 and 15 three types of HLB value. The antibacterial activity of different emulsions against Escherichia coli, Staphylococcus aureus, Bacillus subtilis and Pseudomonas aeruginosa were studied. The potential of spearmint essential oil emulsion for decontamination of red cabbage, lettuce and alfalfa sprouts was evaluated. The main components of the four essential oils are Carvone, Eucalyptol, Linalool, Linalyl acetate, Neral and Geranial. The emulsifying activity and emulsion stability of emulsions treated by shearing homogenizer were lower than ultrasonic and high-pressure homogenizer, because the emulsion layer of ultrasonic and high-pressure type were about 98 %, the water layer of shearing type were about 90 %. The particle size of emulsions within emulsifiers (HLB value 11, 15) treated by ultrasonic and high pressure homogenizer, resulted in smaller particle size, the main distribution was 200 to 400 nm diameter. The other treatment, treated by shearing homogenizer produced 2000 to 4000 nm diameter. The antibacterial activities of four essential oil emulsions treated by different homogenizer showed no significant differences against E. coli. The results suggested that the particle size have no significant relationship with antibacterial activities. The essential oil emulsions have an effect on increasing the antibacterial activity against Gram negative bacteria, because the emulsifier with high HLB value changed the hydrophile of emusion. Lemongrass essential oil served the highest antibacterial activity, followed by spearmint, rosemary and lavender. The Gram negative bacteria were sensitive to the essential oil emulsions, in contrast to the Gram positive bacteria showed higher tolerances. The total viable culture populations in fresh vegetables were decreased when being treated with spearmint essential oil emulsions. However, additional treatment with deionized water showed no difference in population number. The total viable populations of red cabbage and lettuce stored below 4℃ were controlled below sanitation standards of the Department of Health ( DOH ). As the storage temperature is higher than 20℃, the emulsions have no inhibitory effect on population number. The population of alfalfa sprouts reached about 109 CFU/g, treated with emulsions containing 2500 ppm essential oils showed lower effect on decreasing the total viable population.
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