Antimicrobial properties of traditional plant essential oils in solid phase and vapour phase
The antimicrobial properties of cubeb, kaffir lime leaf, citronella, ginger and cinnamon bark essential oils were evaluated in two types of contact tests (solid and vapor phase). The essential oils were tested against two gram-positive bacteria, three gram-negative bacteria, as well as yeast and mold. The antimicrobial strength of each essential oil was expressed in zone of inhibition (ZOI) and minimum inhibitory concentration (MIC) value. The ZOI was measured using disc diffusion assay and disc volatilization assay for solid and vapor phase, respectively. The MIC was determined using broth dilution assay for solid phase and disc volatilization assay for vapor phase. Among all tested oils, cinnamon oil was the most potent antimicrobial agent with ZOI ranged from 18.30 ? 73.40 mm in solid phase and 16.34 ? 60.40 mm in vapor phase and the MIC value were 0.08 ? 0.31 ┬╡l/ml in solid phase and 0.01 ? 0.42 ┬╡l/ml in vapor phase. Together with ginger, cinnamon could be shown to be potential when used in direct contact with the food products, since both oils inhibited better in solid than in vapor phase. Meanwhile, kaffir lime leaf and citronella oils were more suitable for protecting food against Bacillus cereus through indirect contact. Except cinnamon oil, other tested essential oils could not inhibit the gram-negative bacteria.
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