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Antimildew Effects of Plectranthus amboinicus Leaf Essential Oil on Paper

In this study, we evaluated the antimildew effects on paper of Plectranthus amboinicus (Lour.) Spreng leaf essential oil prepared through hydrodistillation. The oil was isolated with a Clevenger-type apparatus and then characterized through gas chromatography with flame ionization detection (GC-FID) and gas chromatography-mass spectrometry (GC-MS). A total of 43 compounds were identified, representing 99.5% of the oil. The main ingredients were carvacrol (50.0%), γ-terpinene (13.1%), and β-caryophyllene (11.3%). The leaf oil had excellent antimildew effects; its minimum inhibitory concentration (MIC) values against Aspergillus clavatus, A. niger, Cladosporium cladosporioides, Chaetomium globosum, Myrothecium verrucaria, Penicillium citrinum, and Trichoderma viride were 100, 200, 75, 75, 100, 150, and 150 μg/cm2 respectively. The leaf oil was further partitioned into 6 derivative fractions (PO1-PO6). PO2 had excellent antimildew effects on the abovementioned strains; at a concentration of 100 μg/cm2, all were 100% inhibited, except A. niger, which was 75.8% inhibited. Carvacrol, the main ingredient of PO2, was then isolated and used for antimildew tests; carvacrol had excellent antimildew activities. Since both P. amboinicus leaf essential oil and carvacrol were proved to have excellent antimildew effects on paper, they are worth further research and development.